Calhoun: The NPS Institutional Archive
Theses and Dissertations
Thesis and Dissertation Collection
1989-09
Optimizing ECM techniques against
monopulse acquisition and tracking radars
Kwon, Ki Hoon
Monterey, California. Naval Postgraduate School
http://hdl.handle.net/10945/26140
-
NAVAL POSTGRADUATE SCHOOL
Monterey
,
California
THESIS
K11
OPTIMIZING ECM TECHNIQUES AGAINST
ACQUISITION
MONOPULSE
AND TRACKING RADARS
by
Kvvon, Ki
I
loon
September 1989
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OPTIMIZING ECM TECHNIQUES AGAINST MONOPULSE ACQUISITION AND
(include security classification)
TRACKING RADARS
Personal Author(s)
Kwon. Ki Hoon
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The views expressed in this thesis are those of the author and do not reflect the official policy or poof the Department of Defense or the U.S. Government.
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sition
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I
continue on reverse
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necessary and identify by block number)
ECM.monopulse.monopulse radar
continue on reverse if necessary and identify by block number)
techniques against monopulse radars, which are generally employed in the Surface-to-Air Missile targeting system,
ire presented and analyzed.
Particularly, these
techniques classified into five different categories, which are; denial
lamming, deception jamming, passive countermeasures, decoys, and destructive countermeasures. The techniques are fully
techniques are
discussed. It was found difficult to quantize the jamming effectiveness of individual techniques, because
nvolved with several complex parameters and they are usually entangled together. Therefore, the methodological approach
tor optimizing
techniques is based on purely conceptual analysis of the techniques.
[19
Abstract
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ECM
ECM
ECM
ECM
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Optimizing
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Techniques Against Monopulse
Acquisition and Tracking Radars
by
Kwon, Ki Hoon
Major, Korean Air Force
B.S.,
Korean Air Force Academy, 1980
Submitted
in partial fulfillment
of the
requirements for the degree of
MASTER OF SCIENCE
IN SYSTEMS ENGINEERING
(ELECTRONIC WARFARE)
from the
NAVAL POSTGRADUATE SCHOOL
September 1989
ABSTRACT
ECM
techniques against monopulse radars, which are generally employed in
the Surface-to-Air Missile targeting system, are presented and analyzed.
ularly, these
ECM
techniques classified into five different categories, which are;
denial jamming, deception jamming, passive countermeasures, decoys,
structive countermeasures.
difficult to
ECM
The techniques
are fully discussed.
It
and de-
was found
quantize the jamming effectiveness of individual techniques, because
techniques are involved with several complex parameters and they are
usually entangled together.
ing
Partic-
ECM
techniques
is
Therefore, the methodological approach for optimiz-
based on purely conceptual analysis of the techniques.
111
.
C.l
TABLE OF CONTENTS
INTRODUCTION
I.
A.
B.
C.
II.
1
BACKGROUND
1
COMPARISON OF SEQUENTIAL AND MONOPULSE RADARS
OVERVIEW
MONOPULSE TRACKING RADAR SYSTEMS
A.
MONOPULSE CONCEPT
B.
TWO
DISTINCTIVE CATEGORIES
1.
Amplitude-Comparison Monopulse Radar
2.
Phase-Comparison Monopulse Radar
ECM TECHNIQUES AGAINST MONOPULSE RADARS
DENTAL JAMMING
A.
III.
C.
6
7
7
7
7
11
15
15
Swept Spot Jamming
16
2.
Barrage Jamming
17
3.
Blinking
17
1
B.
3
DECEPTION JAMMING
20
1.
Range Gate Walkoff
21
2.
Velocity Gate Walkoff
22
3.
Skirt
4.
Delta
5.
Image Jamming
6.
Cross-Polarization
7.
Cross- Eye
PASSIVE
Frequency Jamming
23
Jamming
25
26
Jamming
28
Jamming
30
COUNTERMEASURES
38
1.
Chaff
38
2.
Radar Absorbing Material
40
3.
Stealth
40
IV
D.
E.
DECOYS
41
1.
Expendable Jammer
41
2.
Remotely Piloted Vehicle
42
DESTRUCTIVE COUNTERMEASURES
1.
Anti-Radiation Missile
42
2.
Wild Weasel Tactics
43
ANALYSIS OF ECM TECHNIQUES
IV.
A.
DENIAL JAMMING
C.
D.
E.
45
45
Swept Spot Jamming
46
2.
Barrage Jamming
46
3.
Blinking
47
1
B.
42
DECEPTION JAMMING
47
1.
Range Gate Walkoff
48
2.
Velocity Gate Walkoff
48
3.
Skirt
4.
Delta
5.
Image Jamming
6.
Cross-Polarization
7.
Cross- Eye
PASSIVE
Frequency Jamming
48
Jamming
49
49
Jamming
Jamming
COUNTERMEASURES
49
49
50
1.
Chaff
50
2.
Radar Absorbing Material
51
3.
Stealth
51
DECOYS
52
1
Expendable Jammer
52
2.
Remotely Piloted Vehicle
52
DESTRUCTIVE COUNTERMEASURES
52
1.
Anti-Radiation Missile
52
2.
Wild Weasel Tactics
53
V.
CONCLUSION
LIST
54
OF REFERENCES
57
INITIAL DISTRIBUTION LIST
59
VI
LIST OF FIGURES
Figure
1.
Lobe switching antenna patterns
in
one dimension,
(a)
Polar
form.(b) Rectangular form
Figure
2.
Two
categories of sequential lobing. (a)
tern in
Figure
3.
3
two dimension,
(b)
Lobe switching beam
pat-
Conical scan with 8 beams per scan.
Monopulse antenna patterns (Polar and Rectangular form) and
4.
5.
9
Block diagram of two-coordinate (azimuth and elevation)
amplitude-comparison monopulse tracking radar
Figure
6.
Antenna beam radiation patterns
in
10
phase-comparison
monopulse radar
Figure
7.
er-
Block diagram of amplitude-comparison monopulse radar (one
angular coordinate)
Figure
4
8
ror signal
Figure
.
12
Wavefront phase relationships
in
phase comparison monopulse
radar
13
Figure
S.
Swept spot jamming
16
Figure
9.
Barrage jamming
17
Figure
10.
Figure
1
Figure
12.
Block diagram of the
Figure
13.
Waveform
Figure
14.
Delta jamming block diagram
26
Figure 15.
Image jamming block diagram and waveforms
27
Figure
Block diagram of cross-polarization pulse repeater
28
Figure 17.
Components of
29
Figure
IS.
Cross-eye concept applied to a radar
Figure
19.
Sum
1.
16.
Blinking
jamming waveforms
18
Blinking, synchronized multiaircraft
skirt
19
frequency jamming
of skirt frequency
24
jamming
25
polarization
channels for monopulse receiver,
31
(a)
One
source, (b)
Two
sources
Figure 20.
33
Difference channels for monopulse receiver, (a)
Vll
One
source, (b)
Two
Figure 21.
34
sources
Patterns of the difference channel divided by
sum
channel, (a)
source, (b)
Two
Figure 22.
Warped phase
front
Figure 23.
Block diagram of basic repeater type cross-eye system
Figure 24.
Block diagram of cross-eye system using two separate repeater
One
sources
35
36
37
38
path
Figure 25.
Barrage jamming power vs bandwidth
46
Figure 26.
Block diagram of integrated deception jammer
55
Vlll
LIST OF ABBREVIATIONS
AAA
AGC
Automatic Gain Control
ALARM
Air Launched Anti-Radiation Missile
AM
ARM
DECM
Amplitude Modulation
DINA
Direct Noise Amplification
ECCM
ECM
Electronic Counter Countermeasures
EJ
Expendable Jammer
EW
Electronic
FM
Frequency Modulation
HARM
High-speed Anti-Radiation Missile
IF
Intermediate Frequency
INS
Inertial
IR
Infra
MTI
Moving Target Indicator
PRF
Pulse Repetition Frequency
P\Y
Pulse
RADAR
RAdio Detection And Ranging
RAM
Radar Absorbing Material
RAS
RCS
Radar Absorbing Structure
RF
Radio Frequency
RGWO
Range Gate Walkoff
RPV
Remotely Piloted Vehicle
RWR
SAM
Radar Warning Receiver
Anti-Aircraft Artillery
Anti-Radiation Missile
Deception (Deceptive)
ECM
Electronic Countermeasures
Warfare
Navigation System
Red
Width
Radar Cross Section
Surface-to-Air Missile
IX
SEAD
SNR
STAR
Suppression of
TWS
TWT
UK
Track-While-Scan
Traveling
US
United States
USSR
USAF
Union of Soviet
VGWO
Velocity Gate Walkoff
Enemy Air Defense
Signal-to-Noise Ratio
Supersonic Tactical Anti-Radiation
Wave Tube
United Kingdom
Socialist Republics
United States Air Force
ACKNOWLEDGEMENT
I
am
cordially thankful to
Korean Air Force
I
sincerely
God and
I
wish to express
my
appreciation to the
for providing the opportunity to study.
want
to express
my
gratitude to
my
thesis advisor, Professor R.L.
Partelow, for his patient guidance, dedicated lengthy counsel and consecutive
support during the preparation of
this thesis.
Without
his help
my
effort
would
never have been successful.
I
am
corrects
also very grateful to Professor E.B.
my
Finally,
Rockower, who carefully reads and
script.
I
thank
to
my
wife,
Nam
Kyo,
behalf.
XI
for the
many
sacrifices
made on my
INTRODUCTION
I.
A.
BACKGROUND
(EW) has been
Electronic warfare
seeking out
enemy
targets in either
principally concerned with techniques for
normal or countermeasure environments using
enemy from
such electronic systems as radio or radar or, for preventing the
tecting
friendly targets, using electronic countermeasures
counter countermeasures
tiveness of
ECM. The
interaction between
(ECCM)
development of radar and
its
Electronic
represent techniques for reducing the effec-
EW
development of these
enemy and
(ECM).
de-
techniques was caused by the
friendly electronic systems. This
countermeasures which
is
a typical
was
true of the
example of
this
interaction process.
The word radar was
acronym derived from
a code
name used by
the phrase
the
US Navy
in 1940,
RAdio Detection And Ranging
[Ref.
and
1:
is
an
p.l].
Before world war two, radar had been developed independently and simul-
taneously
in several countries.
widespread due
During world war two, the use of radar became
to the increase of air attacks
by the
allies
and the Germans.
Since the advent of radar, air strikes have not obtained as good results.
order to thwart the operation of radar systems, both sides employed
which were made of thin aluminum
extremely effective
came designated
in
jamming
as "chaff* or
foil strips.
"window"
of electronic warfare were essentially the
[Ref. 2: p.l 15
in
same
&
devices
technique was
These objects be-
p. 252].
1950. the equipment and tactics
as those of world
war two. Nev-
warfare was indispensable by the end of 1951. According to
the official united states air force
would have been
ECM
the radar systems of that time.
During the Korean war which broke out
ertheless, electronic
This kind of
ECM
In
(USAF)
triple the actual losses
without the use of electronic warfare [Ref.
history, the aircraft
during the
3].
last
and crew
losses
two years of the war,
In the
(AAA)
losses
stalled
Vietnam war, surface
to air missiles
campaign during the
greatly impacted the air
from the enemy ground threat, individual
which were
flexible
threat [Ref. 2: p.253, Ref.
In the
Yom
Israeli aircraft
3:
searching for
US
were shot down by the new Egyptian
new
of air operations,
it
SAM
systems which
essential
is
in-
countermeasure techniques or
SAM
30%
and
of the prewar
AAA
systems
systems.
responses to changing threats,
modern warfare,
had "PODS"
This war showed that old countermeasure tech-
and
familiar development pattern of radar
new
reduce the
to the ever-changing radar
Kippur war of October 1973, approximately
is
to
nullify
to destroy
its
countermeasures,
apparent.
utilize acquisition
dars are major threats for hampering air operations.
to
fighters
To
pp.2-3].
niques were inadequate against the
The now
anti-aircraft artillery
initial stages.
jamming systems, adapted
[Ref. 3: p. 3, Ref. 4: pp. 36-39].
In
(SAM) and
the
them.
and tracking
ra-
In order to achieve the goal
SAM
batteries
When we
using
proper
apply countermeasures
radar system, we need an understanding of the various types of radar systems
and
Each type makes use of
their principles of operations.
a variety of different
techniques that are vulnerable to varying degrees.
The main
pioneered
topic of this thesis
in the
US
in
related to
is
the late 1940s
monopulse radar. Monopulse radar,
and early 1950s,
tracking of targets for anti-aircraft missile systems,
the
USSR
for the
same
function.
It
is
intrinsically
earlier conical scan type radars to deceptive type
those
ECM
more
precise
being widely deployed by
much
less
vulnerable than
countermeasures, specifically
techniques which generate spurious data on aircraft position in
azimuth, elevation and range.
Due
to the several
dars, the Soviets have been using increasing
aircraft missile systems, both
The
is
to provide
advantages of monopulse
numbers of them with
ra-
their anti-
ground and ship based.
objective of this thesis
is
to
determine optimum
ECM
techniques which
apply against the monopulse acquisition and tracking radars that are used for
SAM
targeting.
COMPARISON OF SEQUENTIAL AND MONOPULSE RADARS
B.
According
categories.
(TWS)
second,
to angle tracking
They
radar.
TWS
method, tracking radars
are the continuous tracking radar
The
first
radar,
fall
into
two
distinct
and the track-while-scan
provides continuous tracking data on a single target, the
provides
near simultaneous tracking data on multiple
targets.
In continuous tracking radar, the
by
a
antenna
servomechanism actuated by an error
is
pointed at the selected target
signal. Several techniques are
used for
the detection of target angular errors.
One method
ror
is
is
of obtaining the direction and the magnitude of the angular er-
lobe switching, also called sequential switching or sequential lobing, which
done by alternatively changing the antenna beam between two
method generates two overlapping beams which have
in
one coordinate as shown
in
Figure
1
positions.
This
a small angular separation
[Ref. 5: pp. 153- 154].
Switchi ng axis
Beam
Beam
position #1
position
#2
Beam
Beam
position #1
position
#2
# Target
Angle
(a)
Figure
1.
Lobe switching antenna patterns
Rectangular form.
(b)
in
one dimension,
(a)
Polar fonn.(b)
In order for lobe switching to complete angle tracking in elevation
requires a
minimum
This
also true in
azimuth,
it
Figure 2
(a).
is
of four successive
monopulse, but
beam
it is
shown
positions as
not successive
and
in
beams but
simultaneous beams.
Rotation
Azimuth
«*,
\
c
o
>
0)
LU
^r
(b)
(a)
Figure
2.
Tmo
categories of sequential lobing. (a) Lobe switching
two dimension,
Another method
is
(b) Conical scan with 8
conical scanning.
switching technique.
The beam
around the crossover
axis, rather
discrete positions.
It
is
For example,
shown
in
if
is
logical extension of the
is
continuous
lobe
in conical scan,
when each transmitted
the scanning rate
is
pulse re-
forty times per second,
and
320 pulse per second, there are eight beam posi-
Figure 2
and conical scan, are included
scan.
than stepwise motion of the beam between four
Even though the beam motion
the pulse repetition frequency
tions per scan as
a
in
rotates continuously in a circular path, centered
the receiving target echo will be displayed only
aches the target.
beams per
beam pattern
in the
(b).
The above two methods,
lobe switching
general term, sequential lobing [Ref.
6: p. 5].
A
methods
principal source of error in these
caused by fluctuating target cross section.
is
the fluctuation of echo signal
Pulse-to-pulsc amplitude fluctuations
of the echo signal can degrade the accuracy of the tracking radars which need
many
pulses to generate the error signal.
Another disadvantage of sequential lobing
with
its
required four
minimum
is
the limitation on the data rate
successive echo pulses for the complete angle
tracking in azimuth and elevation. This can be a serious limitation in target
There
tracking of large angular accelerations.
mechanical vibration makes
it
is
the further disadvantage that
hard to maintain accurate boresight alignment
in
conical scan radars.
In order to eliminate these
developed.
Monopulse has
and conical scan techniques
Monopulse operation
is
and other problems, monopulse techniques were
several advantages
comparing with lobe switching
[Ref. 6: pp. 6-7].
similar in concept to lobe switching, but instead of
comparing the target echoes obtained from sequential beam positions,
several target echoes simultaneously
of a single pulse.
receives
and then makes the comparisons on the basis
Therefore monopulse can provide a higher data rate than the
other techniques because angle information
Theoretically,
it
monopulse radars are
is
available from every received pulse.
free of errors
due
to pulse-to-pulse fluc-
tuations in target echo intensity because the fluctuations have no effect on the
ratio of signals received simultaneously
Assuming
Ratio
both
less
(SNRj
in
from opposing lobes during each pulse.
that the other radar parameters are the same, the Signal-to-Noise
is
higher
in
monopulse
since the
sum beam
is
pointed at the target
transmission and reception. This results in better detection capability and
tracking error due to thermal noise.
Monopulse has
better stability of the boresight axis because this technique
does not use the mechanical vibration of the feed or reflector.
In sequential lobing techniques, scanning information
unfriendly observer.
which
utilize
It
makes the radar vulnerable
that information.
during tracking.
to
is
disclosed easily to an
some countermeasures
However, monopulse transmission has no scan
In conical scan, the scan rate has an effect
the
beam
direction between transmission
certain limits.
(PRF)
Monopulse
is
cost.
In addition,
matched
one another
C.
to track
monopulse
because
pulse repetition frequency
range
in
monopulse.
the other techniques are complexity
Monopulse requires multiple
need only one.
The
maximum unambiguous
The disadvantages of monopulse over
and high
is
and reception must be the same within
free of this restriction.
the only factor limiting the
is
on tracking range. This
receivers, while the other techniques
receivers
must be well designed and
gain and phase.
in
OVERVIEW
This thesis
is
composed of
five chapters.
Chapter one describes the
differ-
ences between sequential lobing and simultaneous lobing or monopulse tracking
methods.
cially
Chapter two describes the basic principles of monopulse radars, espe-
two
distinctive categories;
amplitude-comparison monopulse and phase-
comparison monopulse. Chapter three contains various
monopulse radars
nial
in
accordance with the
ECM
techniques against
five different categories.
They
are: de-
jamming, deception jamming, passive jamming, decoys, and destructive
methods.
chapter
Chapter four analyzes these
five arrives at the
techniques.
ECM
techniques conceptually.
Finally,
conclusions regarding the employment of the various
MONOPULSE TRACKING RADAR SYSTEMS
II.
A.
MONOPULSE CONCEPT
Sequential-lobing techniques, including conical scan used earlier for target
tracking, are found to be degraded in angle tracking accuracy
target scintillation.
precise direction
To
by the
effects of
eliminate this source of error, the technique for finding
by comparing the return echo on two or more antenna lobes
si-
multaneously was developed. Sequential-lobing tracking radar including conical
minimum
scan require a
of four pulses in order to extract the angle error signal.
Monopulse tracking radar, however, needs
one pulse.
just
Pulse-to-pulse amplitude fluctuations of the echo signal have no effect on
tracking accuracy
rather than
if
the angular
many. There
measurement
are several
be obtained with only a single pulse.
multaneously
in these
is
made on
the basis of one pulse
methods by which angle error data might
More than one antenna beam
used
is
si-
methods, compared with the lobe-switching or conical scan
tracker which use one antenna
beam on
a
time-shared basis.
The angle
direction
of the echo signal can be determined in a single pulse system by measuring the
relative
phase or the relative amplitude of the echo signal received
The names simultaneous lobing and monopulse
ing techniques
in
each beam.
are used to describe those track-
which extract angle error information on the basis of
a single
pulse.
B.
TWO
1.
DISTINCTIVE CATEGORIES
Amplitude-Comparison Monopulse Radar
The
basic amplitude-comparison
two overlapping antenna beams
the target displacement by
These two beams
may
by two adjacent
feeds.
monopulse
to obtain
[Ref.
5:
pp. 160- 164] utilizes
an angle error signal. The radar senses
comparing the amplitude of the received echo
signals.
be generated with a reflector or a lens antenna illuminated
The
basic amplitude-comparison
monopulse system
is
shown
in
target
is
Figure
Figure 3
3.
deviated by an angle
ceived from that side of the
(a)
shows the overlapping antenna patterns.
from the equisignal boresight
beam
difference pattern.
axis the signal re-
pattern has a greater amplitude than that from
Figure 3 (b) shows the
the other side.
If the
The sum pattern
is
sum
pattern and Figure 3
(c)
shows the
used for target amplitude detection and
as a reference signal, while the difference patterns are used for angle discrimi-
Signals received from the
nation.
sum and
the difference patterns are amplified
separately and combined in a phase detector to produce the error signal characteristic
shown
in
Figure 3
(d).
e
(b)
1
Out
of
I
{
In
.
phase
""J
(d)
(c)
Figure
3.
Monopulse antenna patterns (Polar and Rectangular form) and error
sig-
nal.
Amplitude-comparison monopulse radars may be implemented
one or both angular coordinates.
amplitude-comparison
Figure 4 shows a
monopulse radar
for a
in either
block diagram
single angular
of the
coordinate.
The
two adjacent antenna feeds are usually connected with electromagnetic
comparison
circuits
such as a hybrid junction or
The transmission
channels.
line
phase reference information.
tor.
The
The angle
For example,
minus sign
the target
error signal
is
has a only two
provides range and
generated by phase detec-
is
(up/down).
in the case of
azimuth, plus sign could
mean
and
right-side
mean up
case of the elevation, opposite signs
left-side. In
or
down.
If
located on boresight, the difference pattern produces zero magnitude
of angular error.
The
plus
out-phase, relative to the
is
sum channel
It
sign of the difference pattern points out the detected targets direction
relative to boresight (left/right),
signal
connected to the
"magic T".
a
field
sum
and minus signs actually mean in-phase and 180°
The magnitude
or reference channel.
of angle error
proportional to the angular error and the sign of angular error
is
pro-
portional to the targets direction relative to boresight. These angular error signals
control an antenna servo
mechanism
to
perform automatic target tracking
in
an-
gular coordinates.
Transmitter
Sum channel
Duplexer
S
Mixer
IF
Range
Amp
Envelope
signal
detector
magic
Angle-error
TEE
Phase
LO
Mixer
signal
detector
IF
Amp
Antenna
feed horns
Figure
4.
Difference channel
Block diagram of amplitude-comparison monopulse radar (one angular
coordinate).
Even though phase comparison
is
comparison monopulse radar, the angular error signal
comparing the echo amplitudes from simultaneous
lationship between the signals in the offset
phase detector
is
part of amplitude-
intrinsically a
beams
is
offset
is
basically derived
by
The phase
re-
beams.
not used. The purpose of the
to conveniently provide the sign of the error signal.
Transmitter
Range
AGC
LO
9a e
'
,
£T
Duplexer
channel
Elevation
difference
channel
J
F
Envelope
Mixer -e- amp
detector
Phase
IF
Mixer 4*- amp
detector
Video
amp
Range
Elevation angle
error
Azimuth
difference
Mixer
channel
Figure
5.
IF
Phase
amp
detector
Azimuth angle
error
Block diagram of two-coordinate (azimuth and elevation) amplitude-
comparison monopulse tracking radar.
Figure 5 shows a block diagram of an amplitude-comparison monopulse
The
radar with both elevation and azimuth error signals.
makes four
partially overlapping
antenna beams. The feeds might be
a parabolic reflector, Cassegrain antenna, or a lens.
by
all
four feeds.
The
difference pattern in one plane
of two adjacent feeds and subtracting this from the
feeds.
The
cluster of four feeds
The sum pattern
is
10
is
formed
formed by taking the sum
sum
difference pattern in the orthogonal plane
the differences q[ the orthogonal adjacent pairs.
utilized with
of the other two adjacent
is
obtained by combining
Four hybrid junctions generate
three channels which are the
sum
channel, elevation difference channel and
azimuth difference channel. Three separate mixers and IF amplifiers are
one for each channel. All three mixers operate from a single
installed,
local oscillator in
order to maintain the phase relationships between the three channels.
Two
phase
detectors extract the angle error information, one for azimuth, the other for elevation.
Range information
is
extracted from the output of the
sum channel
after
envelope detection.
The monopulse antenna must generate
and
a
sum
pattern with high efficiency
a difference pattern with a large value of slope at the crossover of the offset
beams. The greater the
SNR
and the steeper the slope of the error signal
in the
measurement of
angle.
vicinity of zero angular error, the
more accuracy
in the
Moreover, the sidelobes of both the sum and difference patterns must be low.
The antenna must be capable of
the desired bandwidth, and the patterns
have the desired polarization characteristics.
these properties simultaneously.
It is
must
difficult to fully achieve of all
Thus antenna design
is
an important part of
good monopulse radar operation.
Automatic gain control (AGC)
required in order to keep a stable
is
closed-loop servo system for angle tracking.
accomplished
by
employing
a
The
AGC
proportional
voltage
IF-amplifiers output in order to control the gain of
The
AGC
results in
all
in a
to
monopulse radar
the
is
sum channel
three receiver channels.
a constant angle sensitivity regardless of target size
and
range.
2.
Phase-Comparison Monopulse Radar
In this technique target angle
signals received
5:
pp. 165- 167]
is
sensed by comparing the phase of the
by two separate antennas.
is
similar in
many ways
to
Phase-comparison monopulse [Ref.
amplitude-comparison monopulse.
However, unlike the antennas of amplitude-comparison trackers, those used
phase-comparison systems are not
axis of the
antennas are
offset
parallel.
11
from the
axis.
The
in
individual boresight
Therefore,
if
the target
is
on the antenna boresight
moves
namely,
exists
phase difference which points out the angular
phase.
If the target
is
no phase
off the antenna boresight axis, there
shift,
in
axis, there
error.
l^ ^^
/**
T^""^^^
1
Distance
between
Antenna #1
/boresight axis
antennas
-
Figure
\
l^^^
\ Antenna
[N.
/boresight axis
Antenna beam radiation patterns
6.
in
#2
phase-comparison monopulse radar.
Figure 6 shows the antenna radiation pattern for a phase-comparison
monopulse radar.
Because the antennas radiate separate parallel beams, the
amplitude of the target echo signals coming from far
the
same
value, but the phases are not the
field targets are
same depending on
tances from the target to each of the respective antennas,
phase length differences. This situation
The
tion, as
tenna
1, is
the relative dis-
i.e.,
path length or
illustrated in Figure 7.
of sight to the target makes an angle 6 to the equisignal direc-
line
shown
is
very nearly
in
Figure
7.
R
]
representing the distance to the target from an-
:
*i
and the distance
to the target
R-4-smd
from antenna 2
12
is:
(2.1)
R,
The
= R + 4-smd
difference between these offsets
(2.2)
is
AR = R 2 - R =dsmd
(2.3)
{
This can be used to determine the phase difference
A<p
— = ——
=
-
A
where X
is
the wavelength, and
d
is
a
:
sin
(2.4)
A
distance between two antenna feed horns.
Target
Antenna #2
Antenna #
Figure
7.
Wavefront phase relationships
13
in
phase comparison monopulse radar.
For small angles where
two antennas
signals in the
is
sin
6^0, the phase difference between the echo
:
Atf>*-y-rf0
There
error. It
between phase difference and angular
exists a linear relationship
may
(2.5)
be used to position the antennas via a servo-control loop.
phase-comparison principle, as applied
In the
phase difference between the signals
in
two
to missile guidance, the
fixed antennas
is
measured with a
The servo loop
servo-controlled phase shifter located in one of the arms.
the phase shifter until the difference in phase between the two channels
The amount of phase
shift
measure of the angular
which has
to be
generated to
make
is
adjusts
a null.
a null signal
is
a
error.
Both the amplitude-comparison monopulse and the phase-comparison
monopulse trackers use two antenna beams
for
one coordinate tracking.
measurements carried out by the two systems are
different
from each other.
Therefore the characteristics of the antenna beams will be different,
amplitude-comparison monopulse the two beams point
The
also. In the
in slightly different di-
rections because the antenna difference patterns are offset from the antenna
boresight
line.
This type of pattern can be generated by using one reflector with
two feed horns side by
four feed horns.
Any
side.
For two coordinate tracking,
will require at least
difference in the amplitudes between the two antenna out-
puts in the amplitude-comparison system
and not phase.
it
is
amplitude
a result of differences in
phase-comparison monopulse measures
In contrast with this the
phase differences only and
is
not concerned with amplitude difference.
Even though tracking radars based on the phase-comparison monopulse
principle have been employed, this has not been widely used
angle-tracking techniques.
that the
nas.
sum
The disadvantage of phase-comparison monopulse
signal has higher sidelobes
However,
this
compared with other
due
to the separation of the
is
two anten-
problem can be reduced by overlapping the antenna
apertures.
14
III.
ECM TECHNIQUES AGAINST MONOPULSE RADARS
DENIAL JAMMING
A.
Denial jamming
ceiver so that
used to
its
effective use
denied
is
This terminology
is
also
a noiselike signal
radar receiver bandwidth.
Maximum jamming power
vices,
[Ref. 7: p. 55].
jamming, which consists of transmitting
illustrate noise
in the victim's
defined as the technique that effects a victim radar re-
is
power supply
other components,
limitation,
output depends on the ratings of available de-
power
limitations of waveguides, antenna,
For the jammer
etc.
to get the
maximum power
per unit
bandwidth, the bandwidth should be made as narrow as possible and the
quency spectrum matched
to the victim
fre-
radar receiver. In the most cases, the de-
jamming bandwidth should be greater than
nial
and
allow for frequency set-on tolerances, drift of
the victim receiver
jammer
bandwidth
or receiver, or to
jam
to
se-
veral radar receivers simultaneously.
Denial jamming
is
to
also called noise
is
jamming. The objective of noise jamming
obscure the true target echo by inserting the jammer noise signal into the
victim radar receiver. Noise
jamming
RF
and transmitting the
carrier
wave with
noise,
is
generated by
AM
or
FM
modulating an
result at the victim radar's fre-
quency. The radar receiver detects relatively weak return signals from the target,
therefore radar receivers
must have very high
the radar to be vulnerable to noise
sensitivity.
jamming because
the
This sensitivity causes
jamming
signal
of far greater amplitude than a returning echo signal from a target.
system can detect
SNR
SNR
its
target in a
back ground of ambient
must be much greater than one
is
one or
less,
due
in
from the
target.
15
usually
The radar
However, the
order to reliably detect the target.
to the effects of noise
to evaluate the skin return
noise.
is
jamming, the radar
will not
If
be able
!
1
Denial jamming
is
often classified according to the emission bandwidth of the
jammer. The following techniques can be applied
to the
monopulse acquisition
and tracking radar jamming.
Swept Spot Jamming
1.
Swept spot jamming
quency
is
is
swept across the band. Spot jamming
ming power against one particular
efficiently
quency
In order to
sweep
fre-
capable of concentrating jam-
cannot jam as
it
Nowadays, many radars use
fre-
counter against spot noise jamming.
jam radar systems with both high power density and over
wide frequency band, swept spot jamming
jamming tunes
is
fixed radar frequency, but
an entire radar frequency band.
agile techniques to
jamming where jamming
a kind of denial
the high
power jamming
is
Swept spot
nevertheless employed.
signal across a wide frequency
rates corresponding to the victim radars
if
a
band with
frequency. Thereby
all
pre-
determined victim radars over the desired frequency band including frequency
agile
radars are affected by the jamming signal, as
bandwidth of swept spot jamming thus
bandwidth. This results
in
maximum
Sweep
Figure
8.
"
little
in
The
8.
pp. 273-277].
8:
Agile radar
signal
spot
'
1
i!'r
Figure
bigger than the victim radar
noise quality [Ref.
.'II.
/'
a
shown
1±LL
.
n
Hi
End
End
points
points
Swept spot jamming.
16
'
-
f
Barrage Jamming
2.
Barrage jamming comprises the spreading of noiselike jamming energy
over a wide frequency band, such that
radar can be
jammed
many
victim radars or a single
over a whole radar band simultaneously.
Barrage jamming with wide band noiselike jamming power
many
erated in
broadband
may
be gen-
ways. For example, various types of modulated electromagnetic
waves can be used
for the
low-power sources,
For high-power source devices
rect noise amplification
like
like the traveling
(DINA)
is
semiconductor
wave tube (TWT)
RF
oscillators.
are used.
Di-
produced by passing band-limited Gaussian
noise from a low-power source through a high-power amplifier.
There are several variations of barrage jamming depending on the jam-
ming
circuitry.
Figure 9 shows basic barrage jamming.
Jamming power
density spectrum
Victim radar signals
Figure
3.
-
Barrage jamming.
9.
Blinking
Blinking
jamming
utilizes
noise
jamming whose spectrum covers
the
bandpass of the victim radar and the jamming signal alternately turns on and off
at
approximately a
are
shown
in
50%
Figure
duty cycle [Ref.
10.
17
7:
p.481].
Blinking
jamming waveforms
'
.
'
CL
=>
Spot or barrage noise
o
On-Off
<D
yyyvyvv
O
y y vvvvvvv
/vy
yyVyyv
xxxx
/yv
yvy
y vy y y v
•.
QOOO<XXX
Q.
>CxxVxx'x;
w w yv y y
VvVvVvV VvVvV
y
t v v v v v y v
vvyyvvy
cn
c
E
E
-..,
v
-.'
-
Off
ratio
= P2 / P 1
Sfe
'
>!* ">.'
VV
On
03
—>
Figure
10.
Blinking jamming waveforms.
In order to effectively
should just exceed the time
The jammer
it
jam
a track-on-jam
radar receiver, jammer on time
takes the radar to go into
off time should be just less than the time that
reacquire the target.
Good
blinking
jamming maintains
track-on-jam mode.
its
it
takes the radar to
the radar either searching
for the target or in the process of going into track-on-jam
mode. Typical blink
rates are in the low audio frequency range.
For blinking
to be
most
effective,
two or more synchronized blinking
jammers, which are angularly separated, are required.
In the case of aircraft,
they can be installed on two individual aircraft. These jammers are located within
the radar antennas
beam but
The jammers
at slightly different angles.
are alter-
nately turned on and off so that the victim radar receives the strong noise signal
from alternate angles around
radar
off,
will
attempt
to shift
its
a
mid
point.
The antenna of
tracking direction as the jammers are turned on and
provided that the noise jamming
is
of sufficient strength.
interaircraft control link, this technique can be classified
as
shown
in
Figure
1
a single target-tracking
1
18
by
Depending on the
five different classes,
)
1
Master
Jamming
ff
(
H
I
RF
'
j/lctifTJ
Jamming
&
T ITH
Iradar)
I
ass^
Slave
t
Jamming
Aircr
Aircraft
navigation
gatic
II
1 >
link.
Slave
(
'»
•
lin ks
Viclin
Iradar
Jammlni
Slave
»-
Master
(
IN
No
)
t
Jamming
-
t
Victinj
Iradarl
link
Jamming
I3^*W"I
"•""
Slave
Him
>>
IV
/<
RF
)
rime delay
Jamming
Victim
link
Iradar]
Jamming
1 1 1
1
-
Master
t
Jamming
>>
Sy
Synchronized^
V
digital
A- —
clockO^o
-*-
victim
Iradarl
Jammin
Iffllll
*-
Figure 11.
t
link
Blinking, synchronized multiaircraft.
19
t
When
blinking
jamming source
another
to
in
the control of a missile
is
more
may
turn. This
Otherwise the radar tracker
lock.
from one
cause the radar tracker to break-
have erroneous target information. Thus
will
difficult
will track
and a
missile guided
by the tracking radar
miss the target due to the inaccurate target angle position information.
will
the
working properly, the victim radar
is
maximum
rate
miss distance, the blinking rate must be considered.
too high, the tracker will attenuate the jam signal.
is
missile will be able to
home
in
B.
Hertz [Ref.
it
the blinking
too low, the
is
on one jammer by determining precisely the an-
gular position of individual aircraft.
to ten
If
If
For
Optimum
blinking rates are from one half
9: p.3d-21].
DECEPTION JAMMING
Denial jamming can deny range information, but
and elevation information
employed
radar
to a fire control
at different locations simultaneously.
if
it
may
not deny azimuth
jammers are not
several denial
Thus
a missile
may
hit a target
which has a denial jammer for own self-protection.
However, deception jamming provides a
little
different
method against
control and missile guidance radars in order to decrease the aircraft
bility
by the
missile.
The
objective of deception
jamming
is
to
kill
fire
proba-
confuse or deceive
the true target echo by inserting properly altered replicas of the true target echo
into the victim radar systems. This technique will
correct information
ception
jamming may be
not only
ming
by providing many
in
impossible to get the
in
is
on the display. De-
the accuracy of tracking information
able to degrade
and elevation
it
realistic false targets
range and velocity, but also
related to azimuth
make
azimuth and elevation.
implemented successfully,
If
angle jam-
in general,
it
can cause the victim tracking radar to break lock.
The
tion
with
is
basic
form of deception jamming
to reradiate
time delay.
repeater jamming.
Its
implementa-
modified replicas of the received victim radar signal correlating
The conspicuous
characteristics
coherently store the victim radar signal
frequency
is
memory such
as a
TWT
in the
ECM
combined with
2"
of repeater
set.
This
is
jamming
is
done by using
a delay line in a loop.
to
a
The
output
is
gated out of the loop at successively earlier or later time, simulating
range walk.
The technique employed
to
degrade the accuracy of the azimuth and
vation tracking circuits depends on the tracking technique that
radar. Therefore deceptive
victim
istics
jamming must be matched
is
ele-
used by the
to the character-
of the victim radar.
jamming can be categorized
Typically, deception
on the radar parameter to be "deceived" such
as;
in three
ways, depending
The
range, velocity and angle.
range gate walkoff technique represents range deception, velocity gate walkoff
technique represents doppler deception and several angle deception jamming
techniques are applicable to either the monopulse or sequential lobing acquisition
and tracking radars. Angle deception techniques against monopulse radars can
The
conveniently be divided into two kinds.
advantage of the weaknesses
single source
jamming, image jamming,
techniques
utilize the
example
cross-eye
ception
1.
is
category of angle jamming takes
design of certain monopulse radar systems to
Such techniques are cross-polarization,
jammers.
tort the electromagnetic
in the
first
etc.
The second one
skirt
frequency
uses multiple sources which dis-
wave's angle- of- arrival at the monopulse antenna. These
weakness basic
to all
monopulse tracking systems. Typical
jamming and cooperative repeater
jamming techniques
blinking.
The various
de-
are introduced in the following sections.
Range Gate Walkoff
(RGWO)
Range gate walkoff
is
defined as "a self screening
ECM
tech-
nique for use against automatic range tracking radars that captures the victim
radar's range gate, walks
with no signal" [Ref.
it
off in range,
7: p.l 15].
and then turns
off,
leaving the range gate
There are several other names
for this technique:
range gate capture, pulloff. grabber, grabbing, stealer, deception, dropping,
dumping,
selecting or confusion.
This technique
is
a
fundamental deception
tomatic tracking radars which employ the
target range.
The gate
width of gate
is
is
swiftly controlled
a
range servo mechanism.
varied according to the antenna modes.
21
technique against au-
gate to measure and track the
split
by
ECM
In tracking
The
mode, the
width of gate
mode, the gate
A
tion.
similar in size to the victim radar pulse width.
is
will
be increased
in length to several
corollary function of the gate
which are not within the
is
times the radar pulse dura-
to reject spurious return
The range gate
gate.
is
technique exploits the
characteristics of the range gate to produce range errors.
implemented as follows: [Ref.
(a)
minimum
The victim radar pulse
is
7:
RGWO
True target
received, amplified,
and retransmitted with
to the victim
A
radar receiver.
strong "return'" causes the victim
signal, the "skin return",
is
decreased
(b)
By then gradually
strong repeater signal.
This phase
(c)
is
called the dwell.
gradually walks off from the true target range.
it
As soon
jammer reaches
as the
When
the
and must return
The procedure
is
The walk
off rate
is
walk
the
jammer
turns
limit,
off.
to the acquisition or
it
is
turned
This
off.
the radar has no target
range search routine.
repeated continuously by the jammer thereby con-
tinually interrupting range tracking
2.
is
is
called walk.
the range gate
racy.
circuitry.
increasing the time delay, the range gate tracks the
Hence,
called off or drop.
(d)
AGC
gain and the range gate
in
captured by the strong jamming (beacon) signal. This phase
in
is
pp. 786-787].
radar to decrease the overall receiver gain by the operation of
is
jamming
time delay by the jammer. This provides a strong "return" signal, as a
beacon would,
phase
echo signals
accurately centered at the target
RGWO
return echo during normal radar operation.
typically
In acquisition
in the
and seriously degrading range tracking accu-
range of
1
s
\i
sec for
up
to 10 seconds.
Velocity Gate \\ alkoff
Velocity gate walkoff
(VGWO)
is
defined as "a self screening
ECM
technique for use against automatic velocity tracking radars, that captures the
victim radar's velocity gate, walks
velocity gate with
it
no signal" [Ref.
off in velocity,
7: p. 145].
this technique: velocity gate capture, pulloff,
tion,
and then turns
off,
leaving the
There are several other names for
grabber, grabbing, stealer, decep-
dropping, dumping, selecting or confusion.
Some
radars depend on the doppler shift of the target return echo
der to get the target velocity information.
")->
in or-
The measurement and tracking q[
accomplished by the velocity gate.
VGWO
exploits the charac-
doppler
shift
teristics
of the velocity gate, which tracks the frequency of a strong echo signal.
is
The frequency
shift
operation
serrodyne technique using a
of
TWT.
VGWO jammer can be achieved by the
VGWO jamming can be implemented as fol-
[Ref. 7: pp.937-941].
lows:
(a)
Victim radar signal
is
received, amplified coherently,
and retransmit-
ted to furnish a strong repeated signal, such as a beacon, to the victim radar re-
The strong repeated
ceiver.
signal causes the radar receiver gain to decrease
because of the activation of AGC. As a result of
signal
is
AGC action, the real target echo
suppressed and the repeater captures the velocity gate of the victim radar
receiver. This step
(b)
is
also called dwell period, as in
The doppler frequency of
RGWO.
the repeated signal
sequentially changed,
is
or walked, either in an increasing or decreasing direction. This will cause the vic-
tim radar to track the doppler frequency of the jamming signal rather than that
of the real target.
(c)
Upon
This step
is
the walk phase.
reaching the walk
cause the victim radar to breaklock.
mode and
sition
is
may
Above procedures
VGWO must
ECM
it
is
turned
This will
off.
victim radar then returns to the acquiIf
falsely lock to a spurious
the victim radar fails
low
level signal.
This
the off period.
(d)
and
The
repeater
searches for the targets frequency again.
to reacquire the real target,
step
limit, the
be done
in a
are repeated through such
VGWO
cycle.
RGWO
coordinated manner for most efficient use of these
techniques.
3.
Skirt Frequency
The
Jamming
definition of skirt
jamming
is
that "skirt frequency
jamming
refers to
jamming on
the skirts of the frequency response curve of the radar receiver.
effectiveness
depends on unbalance between the sum and difference channels,
these frequencies, where rapid phase shifts are present in each channel.
it
Its
at
Of course,
can be effectively countered by careful design and construction of the radar"
[Ref.
7: p. 843].
23
Skirt frequency
When
signal
the
ECM
the
which
ECM
is
jamming can
also be used with pulse repeater
set detects the victim
offset
radar signal,
it
will transmit a
from the victim radars frequency. This
produce a beat signal with the victim radar
set will
offset
jamming.
jamming
frequency by
local oscillator.
The
beat signal will appear on each side of the passband spectrum, or on the passband
phase control of the victim radars phase detector
skirts. Stable
attain because of the necessary bandpass.
rors translate into angle-tracking errors
will
be hard to
Consequently, the phase-tracking
er-
by the radar.
\/
7
Pulser
Detector
Direc tional
cou
Dler
i
i
\
rs
TS_
WL/
T\A/
1
Variable
attenuator
Mixer
»-
\s
<
y^
TV n>
i
U^
w
fc
L
Figure
Block diagram of the
12.
skirt
frequency jamming.
Figure 12 shows the block diagram of skirt frequency jamming.
tector provides the input signal to the pulser.
frequency,
/
,
When
A
the received victim radar
fed into the balanced mixer, the balanced mixer generates
sideband jamming signals alf
t
the victim radar
and
f
is
-f and/ + f where/
is
two
the center frequency of
the local oscillator frequency of the
24
de-
jammer.
These
jamming
Figure
signals
13.
contain
very
The victim radar
receiving
little
signal
receiver will detect
frequency where the receiver gain
frequency, as shown
jamming
in
signals at the skirt
rolls off.
Lower sideband
jamming
Upper sideband
jamming
>•
Victim radar
DC
UJ
passband spectrum
-z.
LU
hZ>
Q_
\-
D
o
.
fr-h
Figure
4.
13.
Waveform
Delta
Jamming
Delta jamming
of skirt frequency
is
2
.
radar.
spacing
of/ — f2
is
RF
ECM
signals at
technique that causes erroneous
two different frequencies, f and
x
usually equal to the IF center frequency of the victim
This frequency separation can be controlled so as to
in the victim
radar IF amplifier.
control circuits can be
There
are
+h
jamming.
a self-screening
angle tracking by transmitting two
f The
fr
>r
t
made
several
By forming
false
make
false
IF signals
IF signals, the victim radar
unstable or will have incorrect bias.
other
names
IF-jamming, two-line delta, or RF/IF
delta.
25
for
this
technique:
dual-frequency,
V
Frequency
offset
t
1_
fi
Set on
circuit
Q.
f
(/)
Pulsei
Detector
Cv5
C
Set on
circuit
CO
Frequency
() offset
Figure 14.
Delta jamming block diagram.
Figure 14 shows a delta jamming block diagram for generating two
frequencies.
Two
dars frequency.
set-on oscillators are used to lock on to the received victim ra-
Frequency
jammer frequency
quency.
offset controls of both oscillators allow the locked
5.
fre-
synchronized operation of both power amplifiers, the
In order to allow
TWT
by exact amounts from the victim radars
to be displaced
victim radar pulse detector circuit
power
RF
is
used.
Each set-on
amplifier and radiating antenna [Ref.
7:
oscillator
has
its
own
high
pp. 602-605].
Image Jamming
Image jamming
is
a self-screenig
ECM
technique for use against tracking
radars dependent on phase-sensing for angle tracking, as
monopulse radar. The
definition of
image jamming
is
in
phase-comparison
as follows:
"Image jamming
occurs at the image frequency of the radar, depending on the fact that the phase
angle at IF, between two signals (image frequency and local oscillator)
verse of that which
would appear
frequencies of the receiver.
at the IF
if
the
two signals were
is
at the
the re-
normal
Since the phase-comparison monopulse determines
the direction of the error by the direction of the phase difference between
26
two
signals,
the
image jamming causes the antenna
jamming power exceeds
V
the signal
to be driven
power"
[Ref.
away from
the target
if
7: p. 703].
LO
2 IF
t
Band Stop
Mixer
for
Filter
f.
Pulser
Detector
(a)
o
Upperside
jamming signal
Lowerside
jamming signal
en
c
"e
E
fr
-2
if
tLO
f,
/L0
fr +2
IF
(b)
Image jamming block diagram and waveforms.
Figure 15.
Figure 15 shows an image jamming block diagram and
spectrum.
is
The amplified victim radar
fed into a mixer
jammer
is
RF
TWT
The
RF
an input signal for the pulser, which turns on the
for every input
frequency
amplifier,
signal detector. Local oscillator frequency of the
equal to two times the victim radars IF frequency.
tector provides
TWT
and an
signal through the input
its
radar pulse.
It is
necessary to
best operation.
27
know
signal de-
final
pulsed
the victim radars IF for
In the case
shown
in
Figure 15
(a),
the
band stop
filter
radar frequency,/, and then passes the lower sideband frequency,/
higher sideband frequency,
/ +
21 F,
takes out the
-
21
F and
the
which are used as the image jamming
signals.
Figure 15 (b) shows the frequency spectrum which has the two image
jamming
signals
andfLO
which represent the lower and upper sidebands, where/
represents the victim radar frequency and local oscillator frequency respectively
As an
[Ref. 7: pp. 702-704].
alternative, just one sideband, either the lower or the
upper side of the image jamming
high pass or low pass
6.
is
jamming technique which causes angular
tracking radars, including monopulse.
when
Some monopulse
the received signal
receivi ng signal
is
radars provide erroneous
polarized at right angles to the
t\ /
7
180 phase
TWT
shifter
chain
Horizota lly polarized
recei ving signal
Variable/
a ttenuator
1/
4
Vertically polarized
transmitting signal
\/
71
TWT
chain
16.
simple
error in
Horizontally polarized
transmitting signal
Verticall y polarized
Figure
utilizing a
Jamming
a self-screening
angular information
can be generated by
Filter.
Cross-Polarization
This
signal,
V
A
Block diagram of cross-polarization pulse repeater.
2S
Cross-polarization
of the radar transmitter.
polarization
jamming
[Ref.
7:
pp. 579-585] takes advantage of this characteristics of those radar systems.
Figure 16 shows the repeater system employing two separated cross-
The
polarized receiving and transmitting antennas.
is
horizontally polarized signal
radiated as a vertically polarized signal, and the vertically received signal
phase shifted 180° and radiated as a horizontally polarized
is
signal.
Received
I
/
D°
victim radar signal
vertical component
>
Transmitted
jamming signal
component
/
/
vertical
Received
victim radar signal
\
\
>
Effective transmitted
jamming signal
^\
\j
o
\
^\
Received
1
X
victim radar signal
horizontal component
/
Transmitted \.
jamming signal
horizontal component
A
o
270-
,
>
90
Transmitted
18
0°
jamming signal
horizontal component
(Before reversal)
Figure
17.
Components
of polarization.
Figure 17 shows the polarization components of the signals.
polarization
components of the victim radar
signal appearing at the
The
jamming
platform are dark arrows. The horizontal polarization component of the received
victim radar signal
the
jammer which
is
is
used for producing the vertical polarization component of
then retransmitted to the victim radar antenna through the
29
TWT
amplifier chain without 180° phase shift.
component of the received victim radar
polarization
the horizontal polarization
which
the 180° phase shifter
direction change of the electric field vector.
components are transmitted back
a target
The
Figure 20
is
due
tortion
a
nulls
ECM
is
after
,
TWT
equivalent to a 180°
is
these modified polarization
cross polarized to the skin echo.
sum
each side of boresight as
on boresight, and
null
in
Figure 19
technique that generates angular errors
aircraft or other platform.
ECM
and
(b)
in
monopulse
ra-
two
to the interference
shown
ECM
in
beam
ceive only antenna
sets.
the two
The
ECM
cross eye
to use
is
two
between two jamming sources.
of describing the cross-eye concept [Ref.
7:
pp. 555-576].
is
sources which have equal amplitudes and are 180° out of phase,
Figure
victim radars
The concept of
sources producing either nulls or phase front angular dis-
One method
IS.
This figure shows the aircraft approaching normal to the
direction.
The antenna mounted on
the nose section
which provides the victim radar signal information
received signal
is
is
a re-
to the
two
divided, amplified, and phase controlled so that
sets reradiate repeater
jamming
signals that have the
tude but are 180° out of phase with each other.
make
by 180°
by radiating phase-controlled repeated pulses using separate antennas
out-of-phase
ECM
shifted
is
(b). respectively.
mounted on an
as
When
effects are very similar to cross-eye with a
This
to use
used for producing
Cross-Eye Jamming
7.
dars
is
to the victim radar antenna, they will super-
echo signal which
of difference
pair
signal
component of the jammer and
The function of
amplifier chain.
a
the other hand, the vertical
then retransmitted to the victim radar antenna through a second
it is
impose as
On
a null at the center of the victim radars
30
The two jamming
antenna aperture.
same amplisignals will
«
d/ 2
Transmit antenna
Transmit antenna
P z/180
p
J
jZ ol
e
\
|\
— Receive
4r^:
c/sinGi
\:
i
A
:
*
:
antenna
•
•
•
•
Line of
->^9V<.:
\
\
maximum
ijamming effectiveness
B
A
Radar
Figure
site
Cross-eye concept applied to a radar.
18.
The two transmitting antennas
on each wing.
Thus
are installed
the signal transmitted by the
d
left
feet apart, typically
wing antenna
dsin 6 more than that by the right wing antenna, making the
point on line
AB. Line
AB
will travel
right side null
represents the fact that the radar doesn't have to be
looking perpendicular to the
nulls will occur
first
one
jammer
The
baseline for cross-eye to be effective.
whenever dsin 8 equals
31
n).
where n
is
any integer and
'/.
is
the
radar wavelength. For finding the null positions, two equations can be derived
as follows:
n/.
5
For the
6
first null,
= d sin 6
(3.1)
= rtan0
(3.2)
Solving for 6 and
n should be one.
s,
(sin
6^
tan 6
=
when
small):
is
(33)
"-"""(-jM
iwfl
where
The
As
(3.4).
two
the
is
first null
the null distance from the centerline
r is
the distance from
moves
is
any other
is
cross-eye
jamming
steep spatial
jamming
s. r,
aircraft to victim radar.
and d can be explained from the equation
closer to the radar site
and or the distance between
increased the spacing between nulls, which
effectiveness,
When
(3.4)
angle at the aircraft
relationship between
sets
= r4
s is
the aircraft
ECM
jamming
or
B rad
null.
is
related to the
decreased.
jamming
is
operating, the victim radar receiver detects
lobes of opposite polarity on either side of the centerline,
These lobes are detectable because the jammer signal
is
stronger than the skin return and result in angular tracking errors (usually
azimuth) of
a
few degrees
The following
is
at
figures
most.
show
the relative signal voltage vs scan angle, which
useful for the understanding of cross-eye jamming.
32
c/)
O
>
-10
-20-
LLI
(a)
zz
-30"
LU
DC
-40
A
50
5
,
}
,
-10
-5
^p
Ar
5
10
15
10
15
SCAN ANGLE
if)
-10-
tj
O
>
(b)
-20-
LU
>
<
_l
LLI
DC
-30-
-40"
4-5
-505
-10
9 e
A
5
SCAN ANGLE
Figure 19.
Sum
channels for monopulse receiver, (a)
33
One
source, (b)
Two
sources.
LLI
(3
-10
<
H
-J
o -20
>
LLI
(a)
> -30
H
<
_J
LU
DC
-40
50
5
-10
-5
5
10
15
10
15
SCAN ANGLE
LU
-10
o
>
(b)
-20
LU
> -30
ZZ
<
_i
LU
DC
SCAN ANGLE
Figure 20.
Difference channels for monopulse receiver, (a)
sources.
34
One
source, (b)
Tno
3
CO
o
>
>
<
_l
s
2
r
-
1
I
LLI
(a)
LLI
Boresnght
-
/
I
-1
J
CO
-2
5
I
i
-10
-5
I
I
i
5
10
1
5
10
1
5
SCAN ANGLE
Boresight
3-i
>,
CO
A
2
\
/I
o
>
i
LLI
(b)
>
<
LLI
/
-1
J
-2
5
-10
-5
e
J
o
e
5
SCAN ANGLE
Figure 21.
Patterns of the difference channel divided by
source, (b)
Two
sources.
35
sum
channel, (a)
One
Figure 19 shows the
boresight axis for one source
boresight axis (b).
sum
(a),
channel.
There
is
no
null
point on the
but two sources (cross eye) produce a null on the
Figure 20 shows the difference channel. There
is
a null point
on the boresight axis for one source. But two sources have two null points, each
at the cross-eye angle (6 CE )
on both sides of the boresight
the difference channel divided by the
Figure 3
to
(d).
Figure 21 (b)
is
sum
channel.
Figure 21 shows
axis.
Figure 21
(a)
the result of cross-eye so that the nulls
each side of boresight. Thus the radar can track either null
and Figure 21
(b).
The angle
corresponds to
error (0 CE ) caused by cross-eye
is
in
move, one
Figure 20 (b)
never large.
Phase-front
ECM souyteXT
Pj
,
^8c£
No n-jam
Track direction
Jam
track
direction
Figure 22.
Warped phase
Another way
Under
front.
to describe the cross-eye
concept
cross-eye conditions an interferometry pattern
Figure 22.
This concept
utilizes the the
is
phase front distortion.
is
produced as shown
in
property of any radar tracking antenna
36
which
is
to be aligned with the face parallel (actually tangent) to the
The
of the signal being tracked.
wave
is
tenna
will align itself
shown
of n
The
The peaks
in
Therefore cross-eye
is
known
also
as
re-
phase
Figure 18 correspond to path length differences
and represent the phase front distortion shown
-f-
victim radar an-
with the boresight normal to the distorted phase front,
sulting in angular tracking error.
front distortion.
front
distorted phase front of the electromagnetic
interferometry pattern Figure 22.
in the
wave
a
in
plan-view
in
Figure 22.
A
180 phase
power
shifter
splitter
A
Transmit
antenna #1
Transmit
antenna #2^
A
Receive
antenna
Figure 23.
A
shown
in
Block diagram of basic repeater type cross-eye system.
block diagram of a cross-eye system, which employs a repeater,
Figure 23.
The
previous explanation.
whose output power
is
A
basic concept of the system operation
center receive-only antenna feeds a
split so as to drive
in
effects.
TWT
in
intersect the radar site so as to
Any maneuver
incurring
antenna
37
as the
amplifier
Figure 23 has a basic prob-
that the perpendicular bisector of the line joining the two
must continuously
same
two transmitting antennas with 180°
out of phase signals. However, the system shown
lem
the
is
is
yaw
ECM
antennas
maximize cross-eve jamming
will
degrade
the
jamming
effectiveness.
In order to eliminate this problem,
compensating repeater paths are used as
of the
in
Figure 24.
two transmit and receive antennas
Thus
compensations.
the
two separate, automatically
result
in
The
relative
placements
automatic path length
two signals radiated by the jammers
will
remain 180°
out of phase at the victim radar regardless of the angle of arrival of the victim
radar signal at the jammers
no yaw dependency.
i.e.,
180 phase
shifter
>
>
Traansmit
Transmit
antenna
.antenna
#2
Figure 24.
C.
Block,
diagram of cross-eye system using two separate repeater path.
PASSIVE COUNTERMEASURES
1.
Chaff
Chaff
"window"
in
the
is
one
UK.
It
of
the
is
still
earliest
a
radar
ECM
devices,
also
known
very useful technique, applicable to nearly
as
all
radars except some moving target indicator (MTI) radars.
Chaff consists of resonant dipoles. used
erate multiple echo effects
and
false targets
to reradiate
RF
on the radar display.
energy, to gen-
According
the electromagnetic theory of chaff, a piece of chaff acts like a dipole
3S
to
whose
output terminals are short circuited.
when
reradiation occurs
the
RF
incident
In
the dipole length
energy [Ref.
RF
wavelength of a specified
9:
the case of a
the greatest
approximately a half wavelength of
is
Therefore by cutting to a
p.3L-3].
frequency,
dipolc,
maximum
effect
by the chaff
half
be
will
attained.
Materials used for chaff are conducting or nonconducting fibers coated
with a conducting material
of
aluminum
like
aluminum or
silver-coated nylon thread,
foil,
ducting material. The thickness of a
foil
The general forms
zinc.
and
are ribbons
glass fiber coated with a con-
should be as thin as possible, because the
falling rate decreases the thinner the foil.
Chaff length
or wavelength
wavelength
is
falling rate.
is
is
proportional to the wavelength.
short, chaff length should be short.
long, chaff length should be long.
Chaff
band radars, rope
is
is
not used
If
If
the frequency
the frequency
Long chaff length
is
is
high
low or
increases
its
cover B,
C
combination with other jamming techniques
to
much below 1GHz
for this reason.
To
often used instead of chaff [Ref. 9: p.3L-7].
Chaff can be applied
in
upgrade the effectiveness of jamming. Various chaff missions are also possible.
Representatively, these involve chaff corridor screening, chaff confusion and saturation, chaff deception, signal attenuation,
and self-protection missions.
Chaff corridor screening missions deny
strike aircraft information inside
the corridor to the victim radars. Chaff confusion
and saturation missions over-
load the victim radar scope with false echoes returned by the chaff.
Thus
the
victim radar operator cannot discern the true targets on his radar display. Chaff
deception missions create signals
like
true targets on
the radar displays.
To
achieve this mission, chaff cloud size should be greater than the radar cross section
(RCS) of individual
targets
by an amount equal
provement factor of the victim radars.
after
MTI
In this
way
to the expected
effective returns
MTI
im-
from the chaff
processing should be similar to the returning echo signal from the
air-
craft targets. Signal attenuation missions reduce target detection ranges of the
victim radars.
To
achieve this purpose, chaff clouds must have large chaff density
per unit volume at the victim radar frequencies.
39
The
result
is
the effect of a
greatly increased propagation lose because of the intense
back scattering of the
radar forward energy. Self protection missions deploys chaff
victim radars to break lock on
will
own
when accompanied by
be increased
The
aircraft.
in
order to cause the
effectiveness of this technique
a simultaneous evasive
maneuver
[Ref.
10].
2.
Radar Absorbing Material
Radar absorbing material (RAM)
is
used to reduce the
RCS
by absorb-
ing impinging electromagnetic energy. Thus, the reduced target size will appar-
ently be decreased, along with the target detection range.
One
type of
RAM
surface of the vehicle.
is
The
made by
using a radar semitransparent layer on the
and transmitted energy (50% each) recom-
reflected
bine destructively at the surface, resulting in
good only
narrow band due
a
in
layer [Ref. 11: p. 101].
up
20dB RCS
to
reduction.
to the fixed thickness of the
(approximately
This
is
semitransparent
-H
4
Another type of
wave
electromagnetic
another type of
particles of an iron
RCS
[Ref.
7:
RAM
compound
Such paint can be applied
3.
a dissipator,
p. 405].
to
is
which attenuates the incident
This absorber can reduce the energy
is
It is
an absorbent paint, containing microscopic
Absorbent paint can give
used for absorption mostly above 10 GHz.
almost any aircraft surface but there
is still
a weight
pp.49-50],
12:
Stealth
Stealth has been a highly classified technology untill now.
RAM
re-
usually thicker.
in the ferrite family.
reductions of up to 20 dB.
penalty [Ref.
is
wider frequency band, but
flection over a
Still
RAM
It
combines
techniques with others and can be applied to any kind of weapon system
which can be detected by radar, including
RCS
is
not the only concern
aircraft.
in stealth
technology.
The design concept
of the stealth aircraft also includes avoidance of detection by infra red (IR)
scanner, optical, acoustic,
In reference to
stealth aircraft
is
smoke and
radar
ECM.
contrails [Ref. 13: p. 28].
however, the only interesting point of the
related to detection evasion
40
bv enemy radar. For that reason,
RCS
reduction plays an important role in stealth aircraft. In order for stealth
aircraft to reduce
RAM,
RCS,
RAM
and counter
as discussed above, contributes to
reflective
RCS
geometry can be employed.
reduction by absorbing or atten-
uating incident electromagnetic energy. In addition, radar absorbing structures
(RAS) and radar transparent
structures,
which are constructed of composite
materials, are used to reduce weight as well as
RCS. Two geometric methods
used to scatter the radar beam, rather than reflect
stealth aircraft.
reflection
"One
is
to
make
from the surface of the
it,
the shape flat or rectilinear, concentrating the
on one bearing, and reducing the tendency for concave surfaces
function as retro reflectors over large ranges of angles of incidence.
to scatter the
wave with
a carefully designed
flection." [Ref.
by the USAF.
and the B-2.
D.
Two
14: p. 22].
a stealth
The other
to
is
concave curve of constantly chang-
ing radius, so that each tiny part of the surface has
recently
are
its
own
tiny main-lobe re-
kinds of stealth aircraft have been introduced
F-117A, a
stealth fighter,
based on the
is
first
method,
bomber, combines both methods.
DECOYS
Decoys are
a
support
ECM
techniques that
utilize
low cost vehicles equipped
with different jamming augmentation systems. Decoys can be employed by a variety
of techniques
using different delivery vehicles employing
jammers. Typical examples
and remotely piloted
ol^
vehicles.
this tactics application are
variety of
expendable jammers
These jamming techniques are not peculiar against
monopulse radar systems, but are commonly applied
1.
a
to
any radar.
Expendable Jammer
Expendable jammer (EJ) consists of the jammer and
its
delivery package,
such as parachute, rocket, expendable drone and remotely piloted vehicle (RPV).
Most EJ
may
and cheap. Output jamming power of one unit
are small, light weight,
not be adequate to jam a given radar, therefore, several EJs
to achieve satisfactory
for reuse. This
is
radar capture by decay. By definition, EJ
quite different
The most important
tiveness.
To be
compared with
a recoverable
factor, therefore, in EJ
cost effective, the
life
may
is
be required
not recovered
RPV.
employment
is
cost effec-
cvcle cost of EJs should be less than that of
41
the platform
and alternate
EJ employment are very
ECM,
which the EJs are protecting.
flexible, lending to a variety of scenarios
package and attached jammer.
EJs are dispensed
ploy them by using forward fired rockets, free
towing.
bility,
When
delivering EJs,
if
in several
fall,
ways.
tactics of
of delivery
Aircraft de-
parachute retarded or by
the delivery package does not have flying capa-
parachutes can be used to lengthen jamming time.
Remotely Piloted Vehicle
2.
This tactic
and
The
confuse
to
utilizes a
enemy
drone
radar.
RPV
RPVs
ECM
as
support, to assist strike aircraft
can perform various missions such as jam-
ming, chaff dispensing and EJ delivery.
RPV
conflict
EW
effectiveness as a tool of
between
Israel
and Syria
in the
was demonstrated during
Bekaa Valley, even though not used
use of
RPV
is
RPVs
and
as decoys utilize small radio controlled drones.
The
very cheap compared with using
The primary advantage of
without
loss
the
RPV
is
manned
are small.
aircraft
RCS enhancement
due
14:
aircraft.
use in a high threat environment
of personnel and expensive aircraft.
and shoot down than manned
RPVs
for
p. 112]
decoy delivery but for remotely controlled reconnaissance [Ref.
aircraft simulation.
the 1982
RPVs
arc
more
difficult to detect
Even though
to the their small size.
can be used
to
confuse or deceive
enemy
radar.
E.
DESTRUCTIVE COUNTERMEASURES
I.
Anti-Radiation Missile
The
effectiveness of
get position informations.
SAM
For
systems
this reason,
is
mainly governed by the precise
most
SAM
systems are required to
have targeting radars. These radars greatly enhance the capability of
Meanwhile.
(ARM)
SAM
tar-
SAM.
systems become vulnerable targets of the anti-radiation missile
by working as active emitter.
In the case of high-speed anti-radiation missile
cently developed
ARM
in the
US. operation
is
diation signal either before or after launch.
(HARM),
by locking onto enemy radar
Onboard
RWR
or the
guidance section can detect the enemy radar signal, then the missile
4:
the most re-
is
ra-
missile
locked on
HARM
and homes on the radar.
bands from
2 to
has a wideband seeker which covers
GHz. and has an
40
HARM
width (PW), PRF).
In stand-off
can be fired on a trajectory for
range from high altitude. The highest-priority threat signal
location
HARM
memorized. Then accurate
is
flexibility
of
tactical situation [Ref. 14: p.930].
HARM
mode,
radar
extensive parameter threat library (pulse
has three launch modes which provide
employment, depending on the
all
to continue the attack
even
inertial
selected
and the
navigation system (INS) allow
the radar system
if
is
maximum
is
turned off after the
launch of missile.
In target-of-opportunity
can
in the cockpit. Pilot
select the
mode, the received threat
radar target.
and indicates immediate threats
detects, sorts,
to the aircraft.
Because of these characteristics,
SAM
(RWR)
mode, the radar warning receiver
In self-protection
signals are displayed
HARM
is
capable of coping with
many
radar threats.
2.
Wild Weasel Tactics
"Wild Weasel"
nickname
a
is
for
an aircraft which performs special
missions relating to destruction or suppression of
Their primary mission
is
of mission,
it
air
defense systems.
to provide a safe corridor for the air strike forces using
weapon systems.
integrated
enemy
In order for the
Wild Weasel
to carry out this kind
needs a sophisticated electronic equipment such as
puter system, specialized radar warning and location system and
a
launch com-
ARM
or other
destructive weapons.
Wild Weasel
aircraft
ment of technology. The
In the beginning of
have been continuously updated by the improve-
US Wild Weasel
aircraft
were F-lOOFs and F-105Gs.
Vietnam war, F-lOOFs Wild Weasel
aircraft
were equipped
with an unsophisticated radar warning system designed to intercept and
on the SA-2 radar
They had
cated the
in
signal.
to directly
site,
an effort
to
then
It
home
in
could only detect one target signal at any one time.
in
on the
SAM
radar
site until
the crew visually lo-
come back again and drop conventional bombs on
destrov the
home
SAM
the area
svstems. This tactic was extremelv dangerous
43
because the crew couldn't detect any other
pp. 20-26].
However, low
effective in devastating
with shrike
ARM
level attack of the
enemy
SAM
sites.
sites
near that the area [Ref.
Wild Weasel
In
day was very
in those
1966, Two-seat
15:
F-105G
aircraft
replaced the old Wild Weasel.
After Vietnam, F-4Gs, following F-4Cs, became the primary Weasel
aircraft.
The F-4G Wild Weasel
aircraft
For F-4G Wild Weasels, an airborne
gun
in the
F-4E. This
is
RWR
RWR can detect and
SAM
identify each threat such as
selected target
from outside
craft as future
Wild Weasels.
or
AAA
lethal range.
44
a modified version of
was
sites.
is
enemy radar
aircraft.
20mm
nose
emitters,
and
installed instead of
locate the
USAF
F-4E
Wild Weasel then attacks the
considering F-15 or F-16 air-
ANALYSIS OF ECM TECHNIQUES
IV.
DENIAL JAMMING
A.
Denial jamming or noise jamming
is
not the most efficient method to use
against tracking radars because most tracking radars are able to maintain angle
tracking by locking on to the noise
to tracking radars
may
jamming source may
The
jamming
increase the vulnerability of the
act like a
beacon signal [Ref.
principal effect of the noise type
deny the target range information.
will
A
deny range information
missile system utilizing
effect a kill
In
16:
aircraft since the
p. 138].
jamming against monopulse radar
is
to
monopulse radar systems, denial jamming
the jam-to-signal ratio
if
jamming
jamming
is
equal or greater than one.
monopulse radar guidance may or may not be able
to
without range information, depending on system performance spec-
ifications or missile
ground
source. Applying noise type
However, the operating effectiveness of the
launch range.
degraded without providing accurate range data,
missile system will be
even though modern missile guidance systems can operate with angle data only.
The main advantage of
victim radar system
is
noise
jamming
not required.
and bandwidth of the victim radar
ing, noise
nial
jamming
is
less efficient
Thus
deception jamming.
The
to
The simpler
and blinking, described
may
in
to
know
only the center frequency
perform denial jamming. Generally speak-
than deceptive jamming methods because dethe parameters between the
the circuitry for denial
effectiveness of noise
fectiveness
that precise information about the
One needs
jamming does not accurately match
the victim radar.
is
jamming
is
jammer and
simpler than that for
circuitry generally implies lower cost.
jamming techniques such
chapter three,
is
hard
as swept spot, barrage
to quantify.
The jamming
ef-
be differently evaluated depending on the tactical situation and
available information
these kinds of noise
about enemy weapon systems performance.
jamming
will at least effectively
any radar against which they are employed.
45
However,
degrade the performance of
Swept Spot Jamming
1.
The advantage of swept spot jamming
that
is
it
can concentrate the high
jamming power on each victim radar while sweeping across
band. The disadvantage
time. This
is
that the
jamming
is
wide frequency
intermittent due to the sweeping
drawback can be reduced by increasing
jamming with
a
Swept spot
the sweeping rate.
sweeping rates produces approximately continuous jamming
fast
Again, the optimum rate corresponds to the victims bandwidth, inferred
effects.
from measurements of
his pulse width.
Barrage Jamming
2.
The use of
dars can be
this
type of
jammed without
jammer
is
attractive because frequency agile ra-
readjusting the
jamming frequency,
cause a number of victim radar receivers can be
jammed
at the
as
same
w ell
r
as be-
time.
Equal areas
\
^^
i
^ c
<!>
u'tf
\
•.''.•
*f
^o
"•.'
.-.
3-T3
:<">:
mi mil
i riiiiTii
figft^B^^^I
.
Bandwidth
domain
Bandwidth
domain
:Radar power bandwidth product
[]x.x>|
Figure 25.
bandwidth product
Barrage jamming power vs bandwidth.
As shown
in
Figure 25
jamming power density
width.
Jammer power
is
the disadvantage of barrage
jamming
is
that the
diluted by being spread over a wide frequency band-
The power density of barrage jamming
46
is
inversely proportional to
its
bandwidth. The jamming effectiveness depends on jammer power density.
jamming power
power density
is
If
constant, the wider the jammer's bandwidth the lower the
[Ref. 17: pp. 52-54].
Blinking
3.
This
is
ECM
one of the most effective
ECM
techniques available to the
designer for protecting a formation of aircraft, because
it
works against any type
of tracker including the monopulse tracker.
The disadvantage of blinking jamming
optimum
is
blinking rate, even though the best rate
the tracking servo bandwidth, or in the 0.1 to 10
B.
is
Hz
undoubtedly on the order of
range [Ref.
16: p. 156].
DECEPTION JAMMING
Deception jamming
ECM
generally implemented in the form of the self-screening
is
mission in order to jam against missile guidance which utilizes tracking ra-
dars [Ref. 16:
ble
the difficulty in determining the
to
p. 138].
Self-screening or self-protection
jamming power and
the attack aircraft due to the
limitations on the
noise jamming.
This
is
the
more
applica-
physical size
less
power
to
jam
a
radar compared
because deception jamming uses a waveform
matched
to the victim radar.
mament
loading. In addition, lower
small
is
jammer.
Deception jamming requires significantly
with
jamming
Small
size is desirable to afford
power
more room
availability requires the
for ar-
jammer
to be
size.
Deception jamming techniques discussed
jamming
characteristics.
tively efficient
way
to
RGWO
in
chapter three have different
as range deception technique
is
easy and rela-
jam against monopulse radar because monopulse radars
use a conventional range gate for measuring the distance from radar to target.
VGWO
as velocity deception technique
frequency
shift.
As
a result, the victim
In general, angle deception
is
is
a useful
way
to
induce false doppler
radar can get false range rate information.
difficult to achieve against
monopulse tracking
ra-
dars compared with sequential lobing radars. Monopulse techniques are inherently strong
beams
to
against angle deception
determine
the
target
jamming because they use simultaneous
position.
47
In
order
to
enhance
jamming
effectiveness,
deception
is
it
imperative
ECM (DECM)
to
combine these three categories of
closely
techniques with one another.
Meanwhile, deception jamming systems employ complicated
match the
system
ters
jammed.
characteristics of each type of system to be
demand more
will
expenditure.
To
circuits
Complexity of
properly match the jamming parame-
between the jammer and the victim radar systems, these techniques
quire specific information about the victim radars.
available,
may
it
to
If
will re-
such information
is
not
greatly impact on the use of deception jammers.
Range Gate Walkoff
1.
False target range information in the missile guidance and tracking radar, such as
ror.
SAM
targeting
monopulse radar, can produce aiming-guidance
However, target angle information
good enough
is still
The radar can guide
target angular position.
er-
to direct against the
the semi-active missile with target
angle information only.
In
RGWO,
monopulse radar application of
followed by dropping of the
deceptive signal, the result can be a partial loss of information.
ception
is
If
angular de-
not simultaneously used, the victim radar will reacquire the skin echo
too fast.
2.
Velocity Gate Walkoff
VGWO
itself
may
technique
is
RGWO
very similar to
not be effective against
some radars which employ
measurements because those radars constantly check the
differentiating range data
and comparing
to
technique.
fects of
3.
VGWO
filtering.
If the
VGWO
very
should be combined with
target velocity data
by
jamming
RGWO
signal by
way
of
and angle deception
ef-
little.
Skirt Frequency
Jamming
The jammer used
in skirt
jamming
is
a
little
dars frequency. Well designed monopulse radars
this
by
target doppler
victim radar doesn't exploit the doppler characteristics, the
is
jamming because
RGWO
measured target doppler data.
In order for the victim radar not to reject the
doppler
But
technique.
(}o
detuned from the victim
not ha\e vulnerability to this
technique basically uses the weakness
4v
ra-
in
the design of the
monopulse tracking systems. The tracking accuracy of some monopulse systems
is
degraded
signal
the receiver
if
lies in
not properly tuned to the echo signal so that the echo
the skirts of the IF
Delta
4.
is
filter.
Jamming
Delta jamming technique needs high powered
tennas
each channel
in
bandpass
filters
in
TWT
amplifiers
and high gain an-
order to overcome the high losses by the mixers and
of the monopulse victim radars.
For
effective
jamming, the
information on the victim radars IF bandwidth and IF control frequency are
required.
Image Jamming
5.
This jamming
fective
the
if
6.
is
not a dependable jamming technique because
monopulse radar
is
equipped with an image rejection
Cross-Polarization
Jamming
One advantage
that the cross-polarization
is
ECM
filter
it is
inef-
or mixer.
technique does not
need special knowledge about the victim radar. This provides design freedom
which
important
is
in the
rapidly changing field of
enemy
missile radar control
technology.
The
critical
huge jamming
drawback of
to signal ratios
the cross-polarization
approaching 20
to
40dB
jamming
is
need for
a
This
[Ref. 16: p. 123].
is
because the wave guide components of the victim radar highly attenuate a cross
polarized signal.
sults in a
ponent
is
jamming
any deviation
in the polarization
of the
component with normal
polarization. If the
normal polarization com-
In addition,
greater than the cross-polarization due to the attenuation, the
signal will act as a
It
signal re-
jamming
good target beacon.
has thus far been impractical to employ cross-polarization as the angle
deception jamming technique against monopulse tracking radars.
7.
Cross-Eye Jamming
The magnitude of angular
phase
shift,
and amplitude
fectiveness can be obtained
ratio of
when
error
two
the
is
determined by separation distance,
ECM
jamming
49
sources.
Maximum jamming
signals of the
two
ECM
ef-
sources
are transmitted with 180° phase shift
and
at
equal amplitudes.
separation distances cause proportional angular error,
to
much
span.
effect
it
is
Even though the
difficult to
on the jamming effectiveness because of the limited
implement
aircraft
wing
Separation has an extremely small value compared with the victim radar
range.
The disadvantage of
cross-eye jamming, using one receiving antenna,
dependency on the motion of the jamming
aircraft.
is
The phenomena of warped
phase front occurs near the interferometer peaks. Aircraft movement by yawing
will shift the interferometer null pattern, therefore
Although
greatly degraded.
this fault
jamming
effectiveness can be
can be eliminated by using a cross-eye
system which employs two separate repeaters with equal path lengths,
nique
is
impractical due to cost, weight and complexity constraints.
In order for cross-eye to be effective, high jamming-to-signal
as
much
20dB
as at least
antenna aperture
[Ref. 16: p. 123]. This
relatively small
is
Another major drawback
is
C.
this tech-
is
required,
partly because the victim radar
compared with the
is
is
null spacing.
that the angle error produced by cross-eye
generally very small.
PASSIVE COUNTERMEASURES
1.
Chaff
Even though
against chaff, chaff
is
MTI
still
radar systems can provide some countermeasures
widely used
jam wide bandwidth radars by using
dispenser.
Some
proper length
in
in
military
different
jamming systems.
Chaff can
lengths of chaff in the
same
chaff dispenser systems mounted on aircraft can cut chaff to the
order to match detected victim radars frequency accomplished
through use of RYVR.
Another advantage of chaff
entail high cost to
DECM
provides a very cost effective
utilizing
to angle
monopulse
cost effectiveness.
employ compared with other
paring chaff with the
more susceptible
is
is
techniques.
When com-
techniques against monopulse tracking radar, chaff
ECM.
DECM.
more
ECM
Chaff doesn't usually
Sequential lobing tracking techniques are
However, the angle jamming of tracking radar
difficult
due
5d
to the characteristics of the
monopulse
beam
pattern.
AM
no
The
DECM
modulation
in the
beam
transmitting
Therefore the
DECM
receiver provides
jammer when
to turn
on and
jamming
18:
no information
monopulse
is
when
there
is
tracking.
for directing the
DECM
DECM may accentuate the
DECM angle deception, from a
Sometimes the
not as effective as two source jamming [Ref.
pp.398-399].
On
and the
the other hand, chaff creates a wide spread echo signal
monopulse tracking radar
action of
Monopulse trackers
by
off.
of monopulse radars
aircraft position to the victim radars.
single source, against
beam and
receiver can sense only one steady
is
similar to
will track the strongest
re-
any other tracking radars.
echo signal, which
may
be produced
Chaff can eventually defeat a monopulse tracking radar with proper
chaff.
deployments.
Radar Absorbing Material
2.
In order to use
be considered.
The
RAM
on the
thickness of
aircraft, the
RAM
weight and cost factors must
depends on the frequency. The
effect of
attenuation per unit depth in absorbing material will be increased, as frequency
is
increased. Therefore the thickness of absorber can be decreased as frequency
is
increased.
RAM
coatings are not very practical at low frequencies.
recent trends for the radar systems shows that the frequency
creases
up
to the millimeter region.
Therefore the use of
However,
band gradually
in-
RAM may become more
prominent.
It
will
probably be attended by high cost because of the newness and
complexity of the technique.
3.
Stealth
In fact, even
though sophisticated stealth techniques are employed, one
cannot completely eradicate reflections
SAM
to
a
receiving antenna.
acquisition and tracking radar can detect skin echoes to
pending on the target range and the remaining RCS.
stealth fighter against the
SAM
is
The
based on the fact that
Accordingly,
some
effectiveness of the
SAM
radars have to
acquire normal-sized targets just before the target aircraft reaches
range, and
SAM
has a
minimum range because
51
extent, de-
SAM's
lethal
the missile has a required launch
and acceleration time
fighter.
RCS
SAM
D.
In the case of the stealth
radar picks up the target at considerably shorter range due to
reduction.
range [Ref.
to properly track the target.
The attacker may
therefore be located inside the
minimum
its
firing
12: p. 66].
DECOYS
Expendable Jammer
1.
The
use of EJs against a radar missile system can confuse
operators. Frequently EJs are mistaken for airborne targets.
tempt
to shoot
down
Thus, they
may
at-
EJs with expensive missiles.
Remotely Piloted Vehicle
2.
The primary advantage of
without
loss of
the
RPV
is
personnel and expensive aircraft.
and shoot down than manned
RPVs
enemy radar
are small,
due
aircraft
RCS enhancement
use in a high threat environment
RPVs
are
more
difficult to detect
Even though
to the their small size.
to confuse or deceive
enemy
by homing on the radar radiation.
ARM
can be used
radar.
E.
DESTRUCTIVE COUNTERMEASURES
1.
Anti-Radiation Missile
ARM
directly attacks radars
missiles can be installed
against
SAM
on any type of
A trade off
radars.
aircraft for the
necessary since
is
purpose of
ARMs
utilize
self protection
weapon
stations
on the aircraft thereby reducing the loadout of other primary weapons.
Therefore
ARM
suppression of
enemy
effectiveness of
ARM
air
is
usually delivered by specific aircraft which carry out
defense
against
war and Iran Iraq war.
(SEAD)
SAM
as, for
example the Wild Weasel. The
radars was fully proved during the Vietnam
Several countries have developed and produced
For example. Shrike, high-speed anti-radiation missile
the US;
air
Armat. supersonic
tactical anti-radiation
launched anti-radiation missile
The
use o^
ARM
(ALARM)
for destroying
(HARM)
(STAR)
and sidearm by
missile
by France and
by England.
SAM
systems
will
probably increase
because oi their standoff capability and reduced threat against own
52
ARM.
aircraft.
2.
Wild Weasel Tactics
For the performance of
navigation tactics.
SAM
threat
is
Low
a successful mission,
level flight will
not only
make
Wild Weasel uses low
level
detection hard, but also the
decreased due to the higher ground clutter. This allows Wild
Weasel an increased element of surprise against
recently developed
ARM,
which provides
capability,
and Wild Weasel
pression of
enemy
SAM
tactics
SAM
a longer
sites.
The combination of
range and more flexible launch
can contribute to greatly improved sup-
activities.
53
CONCLUSION
V.
It is
jam radars with one technique
difficult to effectively
Individual
only.
techniques cannot successfully achieve monopulse radar jamming.
It
may
be
impossible to jam the radar completely even under the multiple techniques con-
Each
dition.
ECM
to provide a partial
technique
jamming
be integrated with each other
It is
is
tailored for only a specific portion of the radar
Therefore, several
effect.
ECM
thus desirable to employ the various
As
techniques should
order to completely jam the entire radar systems.
in
possible to enhance the overall
ECM
jamming
illustrated in chapter four,
techniques as simultaneously as
effect.
ECM
some
techniques against monopulse ra-
dars are very impractical. Cross-polarization jamming and cross-eye jamming are
also not
good techniques
for application to
monopulse radars due
ments of very high SNR. Image jamming
is
also not a
to the require-
dependable jamming
technique without special knowledge of the victim radar. However, the other
techniques
that
have
been
have
covered
a
good
effect
on degradation of
monopulse radar performance when combined with one another.
Five different categories of
ECM
techniques against monopulse radar; denial
jamming, deception jamming, passive countermeasures, decoys, and destructive
countermeasures: should be well integrated to give the best result
fectiveness.
Denial jamming techniques have excellent jamming
jamming can be employed by attacking
standoff jamming aircraft.
which
are; range, velocity,
repeater system,
as
very cost effective.
pensing capability.
In deception
in
effects.
In addition.
jamming
RPV
Denial
usually achieved through
and
field.
in
the one
With passive countermeasures, chaff is
Fighter aircraft
RAM
ef-
jamming, the three jamming techniques
Figure 26.
Most attack
expendable drones or
it is
jamming
and angle deception: should be integrated
shown
pact on the future radar
aircraft, but
in
have
self protection
chaff dis-
stealth techniques will certainly imIn
decoy methods, the use of cheap
will greatly increase the survivability of the future
54
When
strike aircraft.
is
considering probability of
theoretically proportional to the
ated by decoys.
number of
the survivability of aircraft
kill,
targets including false targets cre-
Destructive countermeasures can usually be performed by spe-
cially dedicated aircraft
equipped with special weapons,
and attack the position of radar radiation sources.
or Wild Weasel aircraft
a top
is
ARMs,
which can detect
The employment
of
ARMs
growth area, projected well into the next century.
Received victim
Transmitted
radar signal
jamming signal
V
TWT
—
Delay
line
Angle
Velocity
Range
deception
deception
deception
i
i
i
AM
Amplitude Frequency
modulator modulator
detector
Audio-scan
rate
amplitude
modulator
i_
Figure 26.
Time delay
modulator
Swept
oscillator
________
______
Block diagram of integrated deception jammer.
In conclusion, these techniques should be properly integrated to optimize
ECM
techniques while conserving resources against monopulse radars.
The
fol-
lowing combinations are recommended as a best approach for a strike force
package.
55
Attacking aircraft need to be equipped with both passive countermeasures
and integrated deception jammer.
Denial jamming
jamming
relatively
aircraft,
jammers such
confuse the
which require
as decoys can be carried
enemy radar operators
Finally,
performed by the standoff
on any of these
or system.
Wild Weasel type
aircraft to additionally
In relation with these
ECM
tech-
complement the jamming
aircraft
destroying forward or high threat radar systems.
56
Expendable
high output power.
niques, evasive maneuvers have to be included to
fectiveness.
is
with
ARM
take
part
ef-
by
LIST OF
1.
REFERENCES
Eaves, J.L., and Reedy, E.K., Principles of Modern Radar,
Van Nostrand
Reinhold Company,
New
2.
Price, A., Instrument
of Darkness, Peninsula Publishing, Los Altos, 1987.
3.
August, G.
Jr.,
York, 1987.
Radar Electronic Warfare, American
and Astronautics,
A
Institute of
Aeronautics
Inc., 1987.
Call from Wilderness, Air University Review, 1976.
4.
Alberts, D.J.,
5.
Skolnik, M.I., Introduction to
Radar Systems, McGraw-Hill Book Company,
1980.
6.
Sherman, S.M., Monopulse Principles and Techniques, Artech House, 1984.
7.
Van Brunt,
8.
Knorr.
L.B.. Applied
J.B.,
ECM
Vol
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Schleher, D.C., Introduction to Electronic Warfare, Artech
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58
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Optimizing ECM techniques against monopulse
acquisition and tracking
radars.
41