Advanced Radio
and Radar
Part 5
Radar
Introduction
As World War II approached,
scientists and the military were keen to find
a method of detecting aircraft
outside the normal range of eyes and ears.
They found one,
and at first called it
Radio Detection Finding (RDF),
then changed it to
RAdio Detection And Ranging
(RADAR).
Introduction
Radar fires powerful radio waves
towards a target,
and collects the reflected energy.
Radar operators find the position of the target
in terms of range & bearing.
As well as range and bearing
radar can also find another vital fact
about a target aircraft – its height.
Radar Operations
Many factors prevent efficient operation
of a radar system:
Noise – Signals from radio, stars, the atmosphere.
Interference – Man-made signals from other radar
transmitters, electrical apparatus and machinery.
Clutter – Echoes from hills, buildings, sea, clouds,
hail, rain and snow.
Target Characteristics – Shape and composition
have an effect on its echo.
Radar Operations
Many factors prevent efficient operation
of a radar system:
Noise
Interference
Clutter
Much of this
can be reduced
by electronic techniques
Target Characteristics
Types of Radar
There are basically two different types of radar,
Primary and Secondary.
Primary Radar relies solely on the energy
that it has generated and radiated,
being reflected back from the target –
i.e. an echo.
Secondary Radar
has some co-operation from the target –
the target generates its own ‘em’ radiation.
Primary Radar
Primary radar systems may be found in
ground, air, ship or space platforms,
and are used in roles such as:
Surveillance (including weather)
Early Warning
Navigation
Ground Mapping (from space or aircraft)
Guidance Control
Target Detection and Tracking
Terrain Following/Avoidance
Collision Avoidance and Altitude Measurement
Air Traffic Control
Primary Radar
Radars operate in 2 different modes:
Pulse-Modulated Radar (pulsed)
and Continuous Wave Radar (CW).
They operate in the Ultra High Frequency (UHF)
or Super High Frequency (SHF) bands.
This frequency depends on the radar function –
Long range search radar
operates on a relatively low frequency (UHF)
while a weapons system fire control radar
will operate at a very high frequency (SHF)
Primary Radar
APulse-Modulated
pulsed radar uses an
echo principle.
Radar
The transmitter fires a pulse of energy
and then "listens" for an echo to return.
Fires pulse
‘Listens’
Return Echo
The pulses are transmitted at a rate
which determines the range of the radar.
This is called the
Pulse Repetition Frequency (PRF).
Primary Radar
Pulse-Modulated Radar
PRF ranges from 250pps for long-range radars
to 2000pps for short-range radars.
For long-range radar,
1 million watts (megawatt) of (RF) power
is required.
This power is used only during the brief
transmission of the pulse.
The transmitter then ‘rests’ until the next pulse,
and the receiver ‘listens’ for an echo.
Fires pulse
‘listens’
Fires pulse
Primary Radar
Pulse-Modulated Radar
To calculate the distance to the target,
the time for a pulse to travel one mile and return
is known as a "Radar Mile“.
Target Range
1 Kilometre
1 Statute Mile
1 Nautical Mile
Range
1000 m
5280 ft
6080 ft
Return Echo Time
6.67 ms (6μs)
10.75 ms (10μs)
12.36 ms (12μs)
So if we measure the elapsed time between
the transmission and reception of a pulse,
we can use the formula:
Distance = Speed x Time
Primary Radar
The Doppler Effect
Stretch
Squeeze
Relative movement of a sound source
towards and away from a fixed point
causes frequency modulation in the sound wave.
This is a natural phenomenon
Primary Radar
The Doppler Effect
Stretch
Squeeze
A radio transmission from an aircraft
would be affected in exactly the same way.
This is called the Doppler Effect.
Primary Radar
Continuous Wave Radar (CW)
There are two basic types of CW radar.
Continuous Wave Doppler
(CW Doppler)
and
Frequency-Modulated Continuous Wave
(FMCW).
Primary Radar
Continuous Wave Radar (CW)
When the radar sends out a pulse,
if the target is moving towards the transmitter
the reflected waves become bunched up.
CW Doppler
(i.e. they acquire
a higher frequency)
(and vice versa if the target is moving away).
(i.e. they acquire a lower frequency)
Primary Radar
Continuous Wave Radar (CW)
CW Doppler
The radar equipment is able to detect
these small changes in frequency shifts
and so determine the target’s velocity
(speed and direction)
with respect to the transmitter.
A similar system is used by traffic police
with their "speed gun".
This is called the Doppler Effect.
Primary Radar
Continuous Wave Radar (CW)
Frequency-Modulated CW Radar
is a short range measuring radar
capable of determining distance.
It is often used as a “radar altimeter”
to measure the exact height
during the landing procedure of aircraft,
and as early-warning radar,
and proximity sensors.
Primary Radar
Continuous Wave Radar (CW)
Frequency-Modulated CW Radar
The signal is transmitted over a fixed band,
and made to vary in frequency
in a controlled cyclic manner with respect to time.
By measuring the frequency of the returning echo
it is possible to calculate the time interval elapsed
since that frequency was transmitted,
and thus the target’s range.
Primary Radar
Block diagram of a typical radar installation.
MTU
TX
Timebase
Generator
Master Timing Unit (MTU) Produces regular, timed pulses, controlling
the start of the timebase generator .
Timebase Generator
Transmitter (Tx)
Provides the reference signal for the start
of the transmit sequence.
Produces high energy RF pulses in the
range of 400 MHz to 40GHz.
Primary Radar
Block diagram of a typical radar installation.
T/R
Switch
MTU
RX
CRT
Indicator
TX
Timebase
Generator
Transmit/Receive Switch
Aerial
Receiver (Rx)
CRT (Cathode Ray Tube)
Switches both the transmitter and receiver
“ON” and “OFF”.
Used to launch the RF pulses and collect
the returns for processing.
Collects and amplifies the returning echoes
and produces video pulses to the display.
Displays targets to the operator.
Primary Radar
Block diagram of a typical radar installation.
T/R
Switch
MTU
RX
TX
Timebase
Generator
Master Timing Unit (MTU)
Timebase Generator
Transmitter (Tx)
Transmit/Receive Switch
Aerial
Receiver (Rx)
CRT (Cathode Ray Tube)
CRT
Indicator
Secondary Radar
It is vital to know the identity of aircraft
displayed on an air traffic controller’s screen.
Identification Friend or Foe (IFF)
is such a method.
Aircraft are fitted with a transmitter/receiver
(transponder)
which resubmits a reply signal to
an interrogating transmitter/receiver
(interrogator).
IFF equipment is specifically for military use,
the civilian version is called SSR,
Secondary Surveillance Radar
Secondary Radar
The IFF/SSR systems can obtain
specific information from an aircraft.
The aircraft is interrogated on 1030 MHz
using coded pulses or modes.
The aircraft responds on 1090 MHz
using a standard system of codes.
There are 3 modes in use:
Mode 1
Mode 2
Mode 3
Military Aircraft Identify
Military Mission Identify
A) Common Military/Civilian Aircraft Identify
B) Civil Identify
C) Height Encoded Data
Secondary Radar
IFF/SSR systems provide Air Traffic with
information about particular aircraft –
far exceeding that of primary radar.
The types of information available are:
Aircraft height (direct from aircraft’s altimeter)
Direction, Speed and Type of aircraft.
The aircraft can also send
emergency information such as:
Loss of radio communications (code 7600)
Hijack (code 7500)
SOS (code 7700)
Secondary Radar
The main advantages of
IFF/SSR over primary radar are:
a. No clutter problems
(i.e. unwanted returns from rain clouds and mountains)
since transmitter and receiver operate
on different frequencies.
b. Increased range with less transmitted power,
as the radio waves only have to travel one way.
c. More information from each target.
d. Ability to use wide bandwidth receivers.
Check of Understanding
What does RADAR stand for?
Ranging and direction radio
Radio detection and ranging
Ranging and detection radio
Radio direction and ranging
Check of Understanding
Radar detects a target by calculating its . . .
Bearing, Height and Size
Bearing, Height and Range
Height, Range and Velocity
Height, Range and Azimuth
Check of Understanding
In this diagram
What does the block ‘T’ represent?
Timebase
Generator
Rx Unit
Master Timing
Unit
Tx Unit
Check of Understanding
A technique for minimising
clutter in a radar system is:
Increased use of the PRF
Increased electronic countermeasures
Reduction of aerial scanning speed
Reduced by electronic techniques
Check of Understanding
What is the time used in rough calculations
when working in Nautical miles?
1μs
6μs
10μs
12μs
Check of Understanding
The definition of a primary radar is one which:
Is designed to detect targets
at the longest possible range
Utilises the change in frequency of
reflected waves
Receives no co-operation from the target
and relies upon reflection only
Transmits waves which vary in frequency
at a controlled rate
Check of Understanding
In this diagram
What does the block ‘Q’ represent?
Timebase
Generator
Rx Unit
Master Timing
Unit
Tx Unit
Check of Understanding
If a radar energy wave hits a target
and returns with a frequency increase,
what effect is being used?
Demodulation
Frequency Modulation
Pulsed Frequency
Doppler
Check of Understanding
If the frequency of a reflected wave
of a doppler radar decreases slightly,
What is the target doing?
Approaching
Climbing towards the radar
Moving away
Descending towards the radar
Check of Understanding
What is the time unit
used in rough calculations
when working in statue miles?
10μs
12μs
15μs
6μs
Check of Understanding
In this diagram
What does the block ‘S’ represent?
Master Timing Unit
Rx Unit
T/R Switch
Tx Unit
Check of Understanding
The unit in a secondary radar
which re-transmits the signals is called the . . .
Interrogator
Transponder
Coding Unit
Transmit-receive switch
Check of Understanding
Which of the following
is a type of Primary Radar?
Cyclic Wave
Inter-pulsed Wave
Continuous Wave
Carrier Wave
Check of Understanding
Which of these factors
affects radar performance?
Clutter
Frequency
Height of Target
Speed of Target
Check of Understanding
In this diagram
What does the block ‘V’ represent?
Timebase
Generator
CRT Indicator
Rx Unit
Tx Unit
Check of Understanding
What does SSR stand for?
Single side radar
Secondary side radar
Single surveillance radar
Secondary surveillance radar
Check of Understanding
What is IFF used for?
Alerts ATC of the direction of flight.
Tells everyone you are friendly.
Tells other pilots your aircraft is airworthy.
Tells the pilot how many passengers are on board.
Check of Understanding
A pulse radar calculates the target range
by using what?
A pulse long enough
to reach the target
Time between transmission
and receipt of the pulse
A pulse strong enough
to reach the target
Time between the
transmitted pulses
Check of Understanding
In this diagram
What does the block ‘R’ represent?
Master Timing Unit
Rx Unit
T/R Switch
Tx Unit
Check of Understanding
Secondary Radar is defined as a system . . .
Which operates when
the primary radar fails
Where the target responds
with its own echo
Where the target absorbs
the transmitted energy
Where the target reflects
the transmitted energy
Check of Understanding
What is the purpose of
a timebase generator in a radar installation?
Synchronises the
T/R Switch
Provides a reference signal
for the receiver unit
Used to launch the pulses
and collect them on return
Provides a reference signal
to start the transmit sequence
Check of Understanding
A radar using doppler effect
calculates the targets velocity
by measuring what?
Pulse return time
Change of position
Return pulse length
Frequency shift
Check of Understanding
Which of these statements
applies to an SSR receiver?
Multiband
Wide bandwidth
Narrow bandwidth
Single frequency
Check of Understanding
In this diagram
What does the block ‘U’ represent?
Timebase
Generator
CRT Indicator
Rx Unit
Tx Unit
Check of Understanding
In SSR usage,
what does the code 7700 mean?
SOS
Highjack
Height
Loss of radio
Communication
Check of Understanding
What information is given out
with Mode 3C in SSR?
Height encoded data
Military identity
Civil identity
Aircraft type
Check of Understanding
In a radar installation,
what does the Master Timing Unit do?
Switches the timebase generator
on and off
Demodulates the frequency
for the CDT display
Controls the start of the transmitter
and the timebase generator
Produces pulses at the
required level to drive the aerial
Advanced Radio
and Radar
End of Presentation