AIAA 2009-6810
AIAA SPACE 2009 Conference & Exposition
14 - 17 September 2009, Pasadena, California
Space Situational Awareness with an RF Space Warning
Receiver
Arthur J Tardif 1
BAE Systems, Merrimack, New Hampshire 03054
At 5:28 p.m. EST January 11, 2007, the People's Republic of China successfully
destroyed a defunct Chinese weather satellite, FY-1C. The missile was launched from a
mobile Transporter-Erector-Launcher (TEL) vehicle and the warhead destroyed the satellite
in a head-on collision at an extremely high relative velocity. This demonstration crystallized
national attention on the growing threat to US dominance in space. Political and military
leaders are calling for better space situational awareness (SSA) and the ability to accurately
attribute any hostile action to its source. Space warning receivers are a key component of
SSA but legacy systems are too large to be easily accommodated on satellites. This paper
hypothesizes two attack scenarios, direct ascent to destroy a Low Earth Orbit (LEO) satellite
(like the above incident), and a co-orbital attack on a Geostationary Earth Orbit (GEO)
satellite. We point out the use of an RF Space Warning Receiver (RFSWR) that can detect,
characterize and geo-locate a tracking radar on earth to improve SSA. We also explore the
use of an RFSWR to detect and characterize a radar seeker in the terminal guidance phase
of both scenarios. We then compare the performance of state of the art terrestrial receivers
normally used as Radar Warning Receivers against the derived RFSWR requirement. We
then compare the direct sampled RWR demonstrated by BAE Systems against these same
requirements and compared to the conventional RWR. The BAE Systems RWR provides
RF frequency coverage from 500 MHz to 18 GHz in one model, and 26 to 42 GHz in another
millimeter wave (mmw) band maritime application. Both designs are based upon space
capable components. The direct sampling technique used in both product versions
eliminates significant RF front-end circuitry (single and dual stage block down converters,
pre-select filtering and switching, local oscillator generation and distribution, etc.). This
reduction can result in a savings of 2:1 in volume, 3:1 in weight and 6:1 in power
consumption.
I. Introduction
A
T 5:28 p.m. EST January 11, 2007, the People's Republic of China successfully destroyed a defunct Chinese
weather satellite, FY-1C. The destruction was reportedly carried out by an SC-19 ASAT missile with a kinetic
kill warhead. FY-1C was a weather satellite orbiting Earth in polar orbit at an altitude of about 537 miles (865 km),
with a mass of about 750 kg (1,650 lb). The missile was launched from a mobile Transporter-Erector-Launcher
(TEL) vehicle and the warhead destroyed the satellite in a head-on collision at an extremely high relative velocity.
This demonstration crystallized national attention on the growing threat to US dominance in space. Political and
military leaders are calling for better space situational awareness (SSA) and the ability to accurately attribute any
hostile action to its source. Space warning receivers are a key component of SSA but legacy systems are too large to
be easily accommodated on satellites. This paper hypothesizes two attack scenarios, direct ascent to destroy a Low
Earth Orbit satellite (like the above incident), and a co-orbital attack on a GEO stationary satellite. We point out the
use of an RF Space Warning Receiver (RFSWR) that can detect, characterize and geo-locate a tracking radar on
earth to improve SSA. We also explore the use of an RFSWR to detect and characterize a radar seeker in the
terminal guidance phase of both scenarios. From this background information we derive the requirements for a
suitable RFSWR.
1
Staff System Engineer, Space Systems Solutions, PO Box 868, MER 24-116A, Nashua, NH 03061-0868, AIAA
Guest
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American Institute of Aeronautics and Astronautics
Copyright © 2009 by Arthur J Tardif for BAE Systems. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission.
There are a number of underlying desires that provide system requirements. Clearly situation awareness and early
warning are a must to provide time to protect a high value asset (HVA) that may be under attack. Early warning
requires near continuous spatial and RF spectrum coverage. Spatial coverage leads to near earth radius coverage for
nadir facing antennas monitoring space track radars. For proximity awareness, full spherical (4π steredians)
coverage is needed. Full spectral coverage includes from 300 MHz to 18 GHz for the traditional microwave bands
(UHF, L, C, S, X and Ku) and 36 to 40 GHz for the millimeter wave band (Ka). The need to attribute the attack to a
source is key. This need implies characterizing the received RF pulse to accurately classify the source radar. Radars
have unique pulse characteristics including RF frequency; pulse amplitude, width and repetition interval; and
modulation features. With international commerce in weapon systems, the manufacturer of the radar is less
important than the user of the system. Hence, our ability to geo-locate the radar source becomes essential for
attribution. Location relative to the HVA is key to launch an effective countermeasure. At least approximate
direction of arrival of the seeker radar pulses is essential.
We apply these underlying requirements to the attack scenarios, and hypothesize an RFSWR architecture, one for
each scenario. We then compare the performance of state of the art terrestrial receivers normally used as Radar
Warning Receivers against the derived RFSWR requirement. We then compare the direct sampled RWR
demonstrated by BAE Systems Inc. against these same requirements and compared to the conventional RWR. The
BAE Systems RWR provides RF frequency coverage from 500 MHz to 18 GHz in one model, and 26 to 42 GHz in
another millimeter wave band maritime application. Both designs are based upon space capable components. The
direct sampling technique used in both product versions eliminates significant RF front-end circuitry (single and
dual stage block down converters, pre-select filtering and switching, local oscillator generation and distribution,
etc.). This reduction can result in a savings of 2:1 in volume, 3:1 in weight and 6:1 in power consumption. The
BAE Systems design is built on a single circuit card (6” x 9”) suitable for insertion into a PCI backplane. The RWR
provides Pulse Descriptor Words (PDWs) to a host processor. Pulse sorting and emitter matching can be done
onboard the platform or the PDWs can be transmitted to the ground for post processing. Similarly the geolocation
of the earth-based radar can be done in either location.
We close this paper with a look to further technology development to both extend the performance of current
technology and to further reduce its size, mass and power consumption. The current microwave and millimeter
wave designs provide operation across the full RF bands listed while providing unambiguous frequency
measurement over 5 GHz Nyquist bands. Extending the frequency measurement range is clearly desirable.
However, increased performance usually is an attribute that conflicts with a decrease in size, weight and power.
One embodiment of the desired solution is an escort CubeSAT of the 3U size (10cm x 10 cm x 30 cm), weighing
100 kg and consuming only 25 watts of power during full operation. Both packaging and power consumption will
require technology development.
II.
Low Earth Orbit Direct Ascent Attack
The first of two attack scenarios we will address is the LEO Direct Ascent. This scenario is solely from the
author’s imagination and does not reflect any specific knowledge of either the PRC attack cited above or the
subsequent United States of America’s destruction of its rogue satellite.
A. Attack Scenario
Figure 1 illustrates the hypothetical attack. We chose a National Imager as our HVA (bullet 1 in Fig 1). Some
days prior to the attack, a Space Object Surveillance and Identification (SOSI) radar would detect and track the
HVA (bullet 2). This track data is used to compute ephemeris and then used to propagate the orbit forward in time.
Propagating the orbit forward would be part of the mission planning phase. This probably sets the attack window.
At the onset of the attack window, the SOSI or another affiliated space track radar would again establish track of the
HVA, update the ephemeris and cue the ASAT launch (bullet 3). We pictured a two stage ballistic missile vehicle
(bullet 4). The kill vehicle would use a high frequency (perhaps X or Ka band) RF seeker for terminal homing
(bullet 5). Finally the successful kill or disable of the HVA occurs in bullet 6.
From the HVA point of view, we receive radar emissions periodically from various SOSI radars. Some record
of “normal” behavior will be established. Early warning may occur when the SOSI radar departs from normal and
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uses a higher resolution track mode, tracks for an extended period of time, or hands the fine tracking assignment off
to an affiliated radar. Other National Assets should reveal the missile launch. The suspicions of the HVA from
RFSWR data together with a launch detect would put the HVA on alert. The next RF sensor event would be the
illumination by the weapon seeker radar. This radar characteristic is entirely different than that of the ground
tracking radar. It would be characterized by a higher RF frequency, shorter pulse durations and smaller pulse
repetition intervals. The seeker emissions would be received on the nadir facing wide field of view (FOV) antenna,
albeit, probably a millimeter wave band antenna. At this point the HVA would report the attack and undertake
whatever countermeasures are prescribed.
1
LEO High Value Asset
(e.g., National Imager)
6
2
5
Days Prior to Attack:
Radar detects and tracks HVA
Computes ephemeris
Propagates orbit (predict future position)
HVA Destroyed or Disabled
ASAT Target Detection
Kill Vehicle course correction
3
Prior to Attack:
Radar detects and tracks HVA
Computes ephemeris
Verifies path Š provides adjustment info
Cues ASAT launch
Terrestrial Radar
(and/or Terrestrial EO Site)
4
ASAT Launch
Stage separation
Course correction
Control Center
Launch Site
Figure 1. LEO Direct Ascent Attack Scenario
B. RFSWR Requirements for LEO Direct Ascent Attack
The first requirement derived from the scenario is that the RFSWR should have a nadir facing antenna(s) with a
wide field of view (earth radius). This provides the full spatial coverage needed for both SOSI collection and
weapon seeker detection. In fact, the high frequency band antenna should be as wide FOV as possible to detect
shallow attack angles. At least two and probably three frequency bands need coverage. The Low Band should
cover 300 MHz to 2 GHz, a mid-band from 2 GHZ to 18 GHz, and a high band from 26 to 40 GHz. This gives full
spectrum coverage for both track radar and weapon seeker types. Figure 2 illustrates the requirement divided into
the two band requirements.
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Figure 2. RFSWR Requirements for LEO Direct Ascent Scenario. SOSI radars and Weapon Seekers
stimulate dual response
C. Single Receiver Geolocation Technique
Over the past fifteen years, BAE Systems has been developing advanced geo-location techniques applicable to
multiple and single platforms. With the advent of modern digital receivers and high-throughput processors, the real
time implementation of this new class of geo-location techniques has become practical on many tactical platforms,
including space systems. Of particular interest for this program is the TOA Doppler technique using the GRAND
(Geolocation via Random Agile N-platform De-interleaving) algorithm. This algorithm requires a relatively simple
single channel, single platform receiver with fairly accurate time of arrival measurement capability (<30 ns rms
pulse to pulse). The algorithm has successfully been demonstrated at the AFRL Integrated Demonstrations and
Applications Laboratory (IDAL) and in flight tests at Tyndall AFB. Flight testing has demonstrated ranging
accuracies of less than 2% against frequency hopping Radars
We have investigated the viability of the GRAND algorithm on a space-based platform, specifically on a LEO
satellite. Based on our initial simulations, the performance of the GRAND algorithm on this platform exceeds
expectations and is well within the bounds necessary to assign attribution, execute countermeasures or take other
corrective actions. A summary of the simulation parameters and results can be found in Table 1 and Figure 3 below.
Random TOA errors of +/-30 ns and ephemeris position errors of 30 ft in 3 dimensions were used in the simulation.
Table 1. Single Receiver Geolocation Simulation Parameters
Satellite Parameters
Semi-Major Axis (km)
Eccentricity
7068.137
0.0
Inclination (deg)
98.152
RAAN (deg)
49.877
Arg of Perigee (deg)
0.0
True Anomaly (deg)
305.357
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Boresight Angle Error
Geolocation Error (meters)
1
Pointing Error (degs)
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
Geolocation Error
5000
4500
4000
3500
3000
2500
2000
1500
1000
500
20
40
60
Time (Sec.)
80
100
110
0
0
20
40
60
Time (Sec.)
80
100
110
Figure 3. Geolocation Results Converge to Less Than 0.1 Degrees Angle of Arrival And 250 Meters in About 40s
D. RFSWR LEO Architecture
For the past three years, BAE Systems has been developing an RFSWR based upon an architecture that is radical
in nature but proven very successful in the appropriate application. The case of space based SOSI radar collection
and weapon seeker prosecution that we have at hand fits very well. The architecture uses a combination of log video
detection with monobit RF sampling to enable very wide instantaneous measurement bandwidth to be achieved
within the limits of available sampling technology. Both of these non-linear signal processing techniques share a
common trait: they both perform
extremely well in the presence of one
strong signal (greater than 10 dB input
Signal to Noise (SNR). This is precisely
the case with the LEO scenario. The
SOSI radars have extremely high
Effective Isotropic Radiated Power
(EIRP). This radar class stands at least
10 dB above all other radars in EIRP. In
addition, there are only a few of these
radars in the world. The phased arrays
they use are typically built as the side of
a building that houses the electronics.
Prime power is in the Megawatt range.
Received signal strength for a sampling
of typical SOSI radars versus radar
elevation angle for a LEO at both 400
km and 1200 km altitudes is shown in
Figure 4. The input noise levels for the
three receiver channels proposed below
Noise: Low Band -67 dBm, Mid-Band -65, High Band -66
are given at the bottom of the figure.
Given the detection scheme requires 10
Figure 4. SOSI Received Signal Strength at LEO Altitudes.
dB signal to noise ratio (SNR) to make
Greater than 30 dB SNR at 20° elevation and above, typical.
quality measurements, we have a
minimum margin of 20 dB at a 20°
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elevation (typical of SOSI). The weapon seeker also stands alone in the signal environment. Because of its short
range (within 10 km) the RF propagation loss is much less than terrestrial based radars will experience, 120 dB
versus 160 dB. The seeker RF emission will therefore dominate the spectrum.
The notional architecture is shown in Fig. 5. Three bands are proposed. The Low Band would cover 300 MHz
to 2 GHz. We chose to limit the width of the low band to remove the interference that large, Continuous Wave
(CW), low frequency signals (eg. TV stations) may have on the full wideband coverage. The mid- band would
cover 2 to 18 GHz, the balance of the microwave band. Although there are no SOSI radars above about 10 GHz, X
and Ku band seekers are feasible. The first amplification stage is a Successive Detection Log video Amplifier
(SDLVA). This amplifier has two signal outputs: the detected log video (pulse envelop in dBm) and the hard
limited RF carrier. The log video carries the pulse external information: Time of Arrival (TOA), Pulse Width (PW),
and Pulse Amplitude. The RF carrier delivers frequency and modulation characteristics. The log video is sampled
with a multi-bit analog to digital converter (ADC), typically 8 bits. The hard limited RF is first passed through a 90°
phase shift to create the analytic signal. The analytic signal is used to reduce the sampling rate and preclude the
need for a Hilbert Transform to be done digitally, as is proposed for the low band. The 90° phase shift hybrid is
larger in size and more difficult to make perform over the low frequencies.
The measurement algorithms are taken from BAE Systems legacy terrestrial Radar Warning Receiver (RWR)
and Electronic Support Measures (ESM) systems. Log video and Instantaneous Frequency Measurement techniques
have been used for tens of years. We benefit from this experience combined with modern digital implementations.
The algorithms for the three bands are essentially identical with the addition of the Hilbert Transform in the low
band.
125 MHz
Low
Band
Low Band Detection
TOA/PW estimation
8 Bit
V
Hilbert
Transform
1 Bit
H
Low Band Parameter
Measurement
PDW
Generation
4.0 GHz
125 MHz
Mid
Band
8 Bit
R
0
L
90
Mid Band Detection
TOA/PW estimation
1 Bit
Mid Band Parameter
Measurement
1 Bit
PDW
Generation
Software Processing
PDW Sorting
Signal Identification
Geolocation
Emitter Report
Generation
24.0 GHz
125 MHz
High
Band
8 Bit
V
0
H
90
High Band Detection
TOA/PW estimation
Host Resident
1 Bit
High Band Parameter
Measurement
1 Bit
PDW
Generation
FPGA
24.0 GHz
Figure 5. Notional LEO RFSWR Architecture. The proper application of non-linear signal processing techniques
combined with legacy algorithms that are flight tested result in a small, low power highly capable receiver.
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III.
Geostationary Earth Orbit Co-orbital Attack
This attack scenario is purely speculative because we are not aware of any prior demonstrations of this
capability. Launching a GEO satellite is very expensive. To piggy back a smaller weapon on a HVA launch is only
imagined.
A. GEO Attack Scenario
Figure 6 illustrates the hypothetical attack. Again we chose a National Imager as our HVA (bullet 1 in Fig 1).
Some days/months/years prior to the attack, an ASAT is deployed (bullet 2) and slowly pushes to either a super-sync
or sub-sync orbit (bullet 3). It is placed in stand-by mode and left to drift around the GEO belt (bullet 4). Not
depicted here is the regular tracking of both the HVA and the ASAT that will take place by the adversary. Days
prior to the attack, the ASAT will be commanded and then maneuver slowly toward the GEO altitude. The approach
plan was calculated and executed (bullet 5). At the planned time, the ASAT will maneuver into the attack profile, a
targeted descent/ascent on a collision course (bullet 6). With about 10 km of approach distance left the ASAT will
engage his radar seeker (bullet 7) and make final course corrections. Considering size, weight and power limitations
of a relatively small satellite, we’d expect the RF seeker to operate at high frequencies, similar to an anti-air or ship
missile. These are typically X or Ka band.
From the HVA point of view, we receive radar emissions periodically from various SOSI radars. These will
arrive within a narrow angle of nadir, +/- 10 °. Some record of “normal” behavior will be established. Early
warning may occur when the SOSI radar departs from normal and uses a higher resolution track mode, tracks for an
extended period of time, or hands the fine tracking assignment off to an affiliated radar. Friendly SOSI radars should
be tracking the ASAT. A command alert should be possible. The next RF sensor event would be the illumination
by the weapon seeker radar. This radar characteristic is entirely different than that of the ground tracking radar. It
would be characterized by a higher RF frequency, shorter pulse durations and smaller pulse repetition intervals. The
seeker emissions would be received at a shallow angle relative to the satellite horizon, near broadside. A nadirfacing antenna would probably not receive it. At this point the HVA would report the attack and undertake
whatever countermeasures are prescribed.
3
Days/Months/Years Prior to Attack:
ASAT slowly pushed up to super-sync orbit (or sub-sync)
Placed in stand-by mode (awaiting instructions)
Days/Months/Years Prior to Attack:
Adversary launches GEO satellite)
Small covert ASAT also deployed
ASAT drifts around GEO belt
2
4
GEO High Value Asset
(e.g., DSP)
5
Days Prior to Attack:
ASAT gets command to attack
Maneuvers slowly to GEO altitude
Approach plan calculated and executed
1
ASAT target detection
ASAT course correction
HVA Disabled
6
ASAT maneuvers into attack profile
7
Figure 6. GEO Co-orbital Attack Scenario. The first distinct radar emission received may be the weapon
seeker.
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B. RFSWR Requirements for GEO Co-orbital Attack
The first requirement derived from the scenario is that the RFSWR should have a nadir facing antenna(s) with a
narrow field of view (earth radius 17°). This provides the spatial coverage needed for SOSI collection. Near full 4π
steradian coverage is needed for the weapon seeker detection. We envision four antennas arranged to provide 360°
coverage in approximately four quadrants, similar to an Adcock Array. The beamwidth in the vertical direction
should be as broad as possible, similar to a dipole. This array will provide coarse angle of arrival capability (within
90°) with simple amplitude interpolation.To minimize the electronic payload complexity, we recommend time
sharing one receiver channel amongst the four antennas in each band. Figure 7 illustrates the RFSWR for GEO
concept.
SWR Nadir Beam
•Monitor SOSI
•20 deg FOV
•.3 to 10 GHz
•Long Pulses
•Low PRFs
•Very High Power
•Low Density
•ASAT drifts around GEO belt
•Attack Command
HVA Monitors SOSI Radars
HVA Detects ASAT
GEO High Value Asset
(e.g., DSP)
SWR Proximity Beams
•Detect ASAT
•360 Coverage, Wide 4 Quadrant Beams
•Scan Beams for Direction Finding
•8 to 40 GHz
•Short Pulses
•High PRFs
•High Power
•ASAT acquires
HVA with Seeker
•ASAT maneuvers
into attack profile
Figure 7. RFSWR Requirements for GEO Co-orbital Scenario. SOSI radars seen on nadir antenna and
Weapon Seekers on broadside quandrant antenna.
C. RFSWR GEO Architecture
The notional architecture for the GEO RFSWR is shown in Fig. 8. Again three bands are proposed. The Midband covering the nadir antenna would cover 300 MHz to 10 GHz. The primary purpose of this channel is to collect
SOSI radars. At the GEO orbit low frequency interference will not be a factor. So one large band can collect all we
need. The other mid-band and high band receivers service the broadside antennas. The mid-band would cover 8 to
18 GHz, while the high band covers 26 to 40 GHz. The receivers sequence through the four antenna pairs to provide
an azimuth scan. By simply interpolating the amplitude of the pulse reports corresponding to the same emitter can
give a coarse estimate of direction of arrival. Other than RF switches to poll the antennas, the rest of the architecture
matches the LEO RFSWR.
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10 Bit
Nadir
Mid-band
0
90
Proximity
Mid-band
Mid Band Parameter
Measurement
1 Bit
Mid Band Detection
Proximity
High-band
High Band Detection
PDW
Generation
High Band Parameter
Measurement
1 Bit
Processing:
PDW Sorting
Signal ID
Direction Find
Emitter Report
Generation
TOA/PW estimation
1 Bit
4:1
90
TOA/PW estimation
Mid Band Parameter
Measurement
1 Bit
10 Bit
0
PDW
Generation
1 Bit
4:1
90
TOA/PW estimation
1 Bit
10 Bit
0
Mid Band Detection
PDW
Generation
Host
Resident
FPGA
Figure 8. GEO RFSWR Architecture. The same receiver architecture as the LEO RFSWR services the GEO
with a switched bank of broadside antennas for DF.
IV.
Comparison of Log-Monobit RFSWR to Conventional RWRs
A. Traditional Radar Warning Receiver Techniques
Figure 9 shows a typical RWR diagram. It starts with one or more antennas. Multiples may be pointed in
different directions to achieve coverage from all angles, like the GEO architecture. The signals then go through an
RF Tuner function to be converted to an intermediate frequency that can be detected and measured. Detected
signals are then sorted and
identified to determine real
threats and if multiple receivers
operate in parallel a direction
Signal
RF
Tuner
Detection and
may be calculated based on the
RF
Identification
Report
RFTuner
Tuner
Measurement
RF Tuner
and location
amplitude difference between
the RF paths. Finally a report is
sent out either visually, audibly
or electrically to alert users or
higher level system functions of
Figure 9. Typical RWR Functional Diagram
the signal presence.
The Signal identification and location functions have been done in software programmed processors for 30 years
and the Size, Weight, Power and recurring Cost of the function has benefited by 30 years of Moore’s law.
Consequently that portion of the function can be produced for very low size, weight, power and cost. More recently,
detection and measurement functions have been implemented digitally and that portion of the system is starting to
benefit from the advantages of going digital. With time and production volume it will also become less expensive.
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The RF portion on the other hand has been significantly miniaturized, but not fundamentally changed in design. This
has traditionally been the expensive part and with miniaturization, it may even be more expensive depending on the
actual design. The purpose of this program is to eliminate this costly element in the system and go directly from the
RF to digital detection and measurement by direct sampling RF at extremely high sample rates and bandwidths with
only one bit resolution. Currently we have demonstrated instantaneous bandwidths up to 5 GHz and are currently
working to extend that to the 20 GHz of the notional architecture.
B. Impact of SWR on State of the Art
The best way to illustrate the impact of our proposed SWR on the state of the art of Radar Warning Receivers is
to do a side by side comparison of performance characteristics. Table 2 compares the performance of state of the art
ESM receivers currently in production at BAE Systems with the proposed RFSWR. Some of the specifics are
classified and have been omitted. Analog to Digital Conversion has been slowly increasing in sample rate and
bandwidth such that digitizing RF in the 1 to 2 GHz range with 50 dB of dynamic range is now common practice for
ground and airborne systems and the
Table 2. Comparison of State of the Art ESM to RFSWR
processing needed for detection and
Parameter
SOA ESM Systems
SWR
measurement is implemented in
Instantaneous
Bandwidth
4
GHz
20
GHz
modern Field Programmable Gate
Number
of
Channels
8
(500
MHz)
1
Arrays (FPGAs) or other digital
circuitry. Typical RWRs need to
Instantaneous Dynamic Range
50 dB
60 dB
operate with input RF up to 18 GHz
Amplitude Accuracy
1.5 dB
1.0 dB
and more recently up in the 30 to 40
Time of Arrival Accuracy
>15 ns
<10 ns
GHz range. By simply amplifying
Pulse Width Accuracy
>15 ns
<15 ns
the signal until it limits and then
Frequency
Accuracy
Hundreds
of
kilohertz
<
1 MHz
using high speed digital circuits to
MOP
Several types
LFM
sample it, a simple monobit ADC
can be created.
High speed
Size
416 in3
234 in3
telecommunications circuits can
Weight
34 lbs
10 lbs
now perform this sampling function
Power
260 Watts
40 Watts
at rates up to 50 GHz or more and
then convert the samples into
parallel words of 16 or 32 samples each which can be processed by current state of the art FPGA technology.
BAE Systems has developed this technique to perform a phase only measurement function using COTS integrated
circuitry for a space based application. We have employed parts that can directly sample at 5 GHz rates. By direct
sampling higher Nyquist zones up to 18 GHz we are able to make precision phase measurements with the only RF
components being a band limiting filter and an amplifier. We have also demonstrated an Instantaneous Frequency
Measurement (IFM) function as described in US Patent # 7236901 with a sample rate of 5 GHz and good
performance (less than 1 MHz RMS) on input signal frequencies up to the limit of our test equipment at 50 GHz.
C. Future Technology Development
A primary goal in the future is to develop techniques to increase our instantaneous bandwidth while keeping
size and power under control. This will enable enhanced Probability of Intercept (POI) at good sensitivity or a net
smaller implementation depending on specific platform requirements. Today we are using discrete packaged
components for the monobit sampling and deserializing. Clearly a multi-chip module or a higher level of integration
will reduce both size and power consumption. A good deal of power is consumed in the driver and receiver circuitry
needed between packages. Higher integration would eliminate most of this waste. We have developed a concept for
a mixed signal ASIC that would provide the desired integration. We are now looking for a source of funding. In
addition to raw sampling speed, algorithm refinement is also required. Todays and tomorrows FPGAs and ASICs
will not keep pace with the fourfold increase in sampling rate. The advancement of RFSWR technology bodes well
for the proliferation of such devices to be install unobtrusively on future high value assets. Furthermore, with the
right size, weight and power an RFSWR could be hosted on something as small as a cubesat. Then we could add
protection to current HVAs already in orbit.
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