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- 1. Professional Development Short Course On: ELINT Interception and Analysis Instructor: Richard G. Wiley, Ph. D. ATI Course Schedule: http://www.ATIcourses.com/schedule.htm ATI's Space Based Radar: http://www.aticourses.com/ELINT_analysis_3.htm
- 2. ELINT Interception and Analysis Summary The course covers methods to intercept radar and other non- communication signals and a then how to analyze the signals to determine their functions and capabilities. Practical exercises illustrate the principles involved. Participants receive the hardcover textbook, ELINT: The Interception and Analysis of Radar Signals by the instructor. Instructor Richard G. Wiley, Ph. D. is vice president and chief scientist of Research Assocaites of Syracuse, Inc. He has worked in ELINT since the 1960s. He has published 5 books, including the textbook for this course, as well as may technical papers. His accomplishments include the first fielded computer based TOA system and the first receiver specifically designed to Course Outline intercept LPI radar signals. He was co founder of Research Day 1 Associates of Syracuse which provides technical solutions for • Character and uses of ELINT today’s ELINT environment. • Radar fundamentals • RF generation and propagation • Noise figure and bandwidth What You Will Learn • Sensitivity and dynamic range • Pulse density vs altitude • Special Characteristics of Receivers designed for • ELINT range advantage ELINT Day 2 o Uses for Wideband receivers not • Crystal video receivers generally used in radar and • Noise limited vs gain limited communications systems • Superhet receivers o Application of Probability of • Analog and digital IFM receivers Interception theory using several examples • Channelized and Bragg Cell receivers The ELINT advantage of one way vs radar’s two • Microscan and other receivers • way propagation • Modern phase processing receivers • Direction Finding and Emitter Location problems • Direction finding techniques and solutions Day 3 o How TDOA and FDOA location • Emitter location via triangulation techniques work • Time difference of arrival (TDOA) o Error ellipses and their applications to • Probability of Interception real world systems • ERP analysis • Antenna basics from both the interception and • Polarization analysis radar signal analysis viewpoints • Beam shape analysis • RF Coherence, why it is important and how to • Antenna scan analysis measure it • Pulse shape analysis • Intrapulse Modulation, both intentional (pulse compression) and unintentional Day 4 PRI Measurement and Analysis • Intrapulse modulation • o Stagger and Jitter and other types of • Wideband signals PRI modulation definitions and analysis • PRI Types techniques • MTI and pulse Doppler analysis o Effects of noise, scanning and platform • PRI measurement problems motion • Deinterleaving o Optimum methods of analysis under • Delta-T and other histograms different conditions • RF analysis and coherence Measures o Time based deinterleaving methods • ELINT parameter limits • Introduction to ELINT data files and applications • LPI Radar and the future of ELINT to EW systems
- 3. www.ATIcourses.com Boost Your Skills 349 Berkshire Drive Riva, Maryland 21140 with On-Site Courses Telephone 1-888-501-2100 / (410) 965-8805 Tailored to Your Needs Fax (410) 956-5785 Email: ATI@ATIcourses.com The Applied Technology Institute specializes in training programs for technical professionals. Our courses keep you current in the state-of-the-art technology that is essential to keep your company on the cutting edge in today’s highly competitive marketplace. Since 1984, ATI has earned the trust of training departments nationwide, and has presented on-site training at the major Navy, Air Force and NASA centers, and for a large number of contractors. Our training increases effectiveness and productivity. Learn from the proven best. For a Free On-Site Quote Visit Us At: http://www.ATIcourses.com/free_onsite_quote.asp For Our Current Public Course Schedule Go To: http://www.ATIcourses.com/schedule.htm
- 4. Low Probability of Interception • The radar designer tries to make the signal weak • Then the ESM system cannot detect it. • For radar this can be difficult. • Spread Spectrum is a term used in communications. (I say it does not apply to radar!)
- 5. Radar is not “Spread Spectrum” • In communications, the transmitted spectrum is spread over an arbitrarily wide band. The spreading is removed in the receiver. The interceptor may not be able to detect the wideband signal in noise. • In radar, the transmitted bandwidth determines range resolution. Wideband signals break up the echo and thus reduce target detectability – what you transmit is what you get back – synchronizing the receiver is the ranging process
- 6. Modern Radar Waveforms • Energy on target, not peak power determines radar performance • A CW radar has peak power 30 dB lower than a pulsed radar with a duty factor of .001, e.g. 1 microsecond Pulse Duration and 1 millisecond PRI. • Frequency or Phase Modulation is needed to obtain the desired Range Resolution
- 7. Intercepting Modern Radar • Lower Peak Power helps the radar • Earlier Radar designs were concerned with target detection and with ECM • Today’s radar designs are also concerned with Countering ESM (Intercept Receivers) • Tomorrow’s Intercept Receivers must cope with new types of Radar Signals
- 8. CW Radar Reduces Peak Power Power Pulse-High Peak Power CW--Low Peak Power Time
- 9. Range Equations Signal received from the target by the radar receiver varies as range to the -4 power Pt Gt Gr 2 SR ( 4 ) R 3 4 Signal received at the ESM receiver varies as range to the -2 power Pt Gt GE 2 SE ( 4 ) 2 RE 2
- 10. Receiver Sensitivities Compared The radar receiver needs certain minimum signal level to do its job. Likewise the ESM receiver needs a certain minimum signal level to do its job. We can compare these: S E (min) NoiseBWofInt.Rx. ~ S R (min) NoiseBWofRadarRx
- 11. Intercept Range/Radar Range 4 1/2 RE 1 G TEG E LE = RR (1) RR GT G R LR Note that the ratio of the radar receiver sensitivity to the ESM receiver sensitivity is in the denominator; if the radar receiver is more sensitive the ratio of the ESM range to the Radar range is reduced
- 12. Example for Pulsed Radar Designs • Radar range =100 km • RCS =1 sq meter • Rx Ant Gain =1, Sidelobe Tx Ant. Gain=1 • ESM Rx 20 dB poorer sensitivity than Radar Rx • The Sidelobes of the Radar can be detected by ESM at a range of over 30 times the range at which the radar can detect its target • Main beam detection over1000 times Radar Range
- 13. Frequency/Time for Modern Radar Signals Frequency Agility Band (Depends on Frequency Component * Design, ECM Factors, Designer Ingenuity) Coherent Processing Interval (depends on radar mission) Time *BandwidthDepends on Radar Mission Which Determines Range Resolution
- 14. Types of “LPI” Radar Modulation • FMCW (“Chirp”) • Phase Reversals (BPSK) • Other Phase Modulations (QPSK, M-ary PSK) • In short, any of the pulse compression modulations used by conventional radar.
- 15. ESM Receiver Strategies • Detection of a radar using only the energy has the advantage that the ESM detection performance is largely independent of the radar waveform • Detection based on specific properties of the radar signal can be more efficient • Radar usage of code/modulation diversity may defeat ESM systems designed for specific signal properties
- 16. Range Comparisons for Pilot Radar Radar Range ESM Range Target ESM Cross-section Radar Range (km) Sensitivity ESM Range (km) 10KW Pulsed 1W FMCW 10KW Pulsed 1W FMCW 2 (m ) Radar Radar -dBmi Radar Radar 10 15 16 -60 250 2.5 100 26 28 -80 2,500 25 1,000 46 0 Intercept Range/Radar Range=2.5/16=.156 =25/28=.893
- 17. Non-coherent Approach • Rapid Sweep Superhet Receiver (RSSR) proved usefulness of noncoherent or post- detection integration against LPI signals • Technique should be routinely applied to processing wideband receiver outputs for discovering LPI signals • Sensitivity improves with square root of n, number of sweeps per pulse • Hough transform can be applied when chirp exceeds processor IF bandwidth
- 18. Frequency Versus Time: Environment and RSSR Sweeps Detection announced using 4 of 8 rule Frequency (MHz) 2000 MHz 0 20 40 60 80 100 120 140 160 180 200 Time (s) Note: 1. This shows one long pulse/CW (pulse compression) of low SNR with eight low duty cycle pulse trains of high SNR. 2. RSSR outputs for M=4, N=8 begin at the fourth sweep or . X provides no output. 3. Microscan outputs occur for all of the strong short pulses but not the weak long pulses.
- 19. Envelope Techniques • RSSR uses many samples of the envelope prior to making a detection decision • Various M/M, M/N and other statistical techniques for sensitivity enhancement can be used • The past analog implementations could be done digitally in software and applied to a wideband digital data stream
- 20. Required IF SNR Pd=.9, Pfa=1E-6 (single Pulse SNR=13.2dB) • M/N integration; N determined by signal duration during its Coherent Processing Interval or Pulse Width (M optimized). • Note: PW values shown are for 512 MHz Sweep Band. Reducing the Sweep to 256 MHz reduces the minimum PW by a factor of two. • N=8 N=16 N=32 N=64 • PW>160us PW>320us PW>640us PW>1320us • M=4 M=6 M=8 M=12 • SNR=7.3dB SNR=5.4dB SNR=3.4dB SNR=1.7dB • Gain=5.9dB Gain=7.8dB Gain=9.8dB Gain=11.5dB
- 21. M/N Integration; N Large Detection and False Alarm Probabilities IF SNR=-1.5 dB Pd,1=.118; Pfa,1= .0298 1.2 Pd, 256=.9; pfa, 256=.000001 Threshold =2.65 1 0.8 Probability or Density 0.6 0.4 0.2 0 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4 Normalized Detector Output
- 22. Time-Frequency Transforms (Relationships and Descriptions) • Wigner-Ville Distribution (WVD) – Good Time-Frequency resolution – Cross-term interference (for multiple signals), which is: • Strongly oscillatory • Twice the magnitude of autoterms • Midway between autoterms • Lower in energy for autoterms which are further apart • Ambiguity Function (AF) – AF is the 2D Fourier Transform of the WVD – A correlative Time-Frequency distribution • Choi-Williams Distribution (CWD) – Used to suppress WVD cross-term interference (for multiple signals), though preserves horizontal/vertical cross-terms in T-F plane – Basically a low-pass filter • Time-Frequency Distribution Series (Gabor Spectrogram) (TFDS) – Used to suppress WVD cross-term interference (for multiple signals) by: • Decomposing WVD into Gabor expansion • Selecting only lower order harmonics (which filters cross-term interference)
- 23. Time-Frequency Transforms (Relationships and Descriptions – cont’d) • Short-Time Fourier Transform (STFT) – STFT is a sliding windowed Fourier Transform – Cannot accommodate both time and frequency resolution simultaneously – Square of STFT is Spectrogram (which is the convolution of the WVD of the signal and analysis function) – Not well suited for analyzing signals whose spectral content varies rapidly with time • Hough (Radon) Transform (HT) – Discrete HT equals discrete Radon Transform – A mapping from image space to parameter space – Used in addition to T-F transform for detection of straight lines and other curves – Detection achieved by establishing a threshold value for amplitude of HT spike • Fractional Fourier Transform (FrFT) – The FrFT is the operation which corresponds to the rotation of the WVD – The Radon Wigner Transform is the squared magnitude of the FrFT – Main application may be a fast computation of the AF and WVD • Cyclostationary Spectral Density (CSD) – CSD is the FT of the Cyclic Autocorrelation Function (CAF) – CAF is basically the same as the AF – CSD emphasis is to find periodicities in the CAF (or AF)
- 24. Ambiguity Function then Hough Transform of FMCW Signal-SNR -10dB 80000 60000 Radon Freq Transform shift Magnitude 40000 20000 -2*10^12 -1*10^12 0 1*10^12 2*10^12 Time Lag FM Slope Ambiguity Function Hough Transform Peaks of Hough Transform show the positive and negatives slopes of the triangular FM waveform
- 25. WVD and CWD comparison for LFM signal (SNR -15dB) 20 40 60 80 100 120 20 40 60 80 100 120 WVD of LFM signal in noise HT of WVD of LFM signal in noise CWD of LFM signal in noise HT of CWD of LFM signal in noise WVD has better T-F resolution and a ‘tighter’ HT spike. 1 WVD/CWD line maps to 1 HT spike. Detection achieved via establishing a threshold value for the amplitude of the HT spike
- 26. WVD and CWD comparison for 2 LFM signals (SNR -3dB) WVD of 2 LFM signals in noise HT of WVD of 2 LFM signals in noise CWD of 2 LFM signals in noise HT of CWD of 2 LFM signals in noise WVD has better T-F resolution and ‘tighter’ HT spikes. CWD suppresses some cross-term interference, but preserves horiz/vert cross-terms. 2 WVD/CWD lines map to 2 HT spikes. Detection via HT ampl. threshold
- 27. STFT of LFM signal and of 2 LFM signals (SNR -3dB) STFT of LFM signal in noise HT of STFT of LFM signal in noise STFT of 2 LFM signals in noise HT of STFT of 2 LFM signals in noise 1 STFT line maps to 1 HT spike; 2 STFT lines map to 2 HT spikes. STFT T-F resolution inferior to that of WVD (STFT- window funct. imposes resolution limit). STFT superior to WVD for cross-term interf. Detection via HT ampl. threshold
- 28. CWD for a BPSK signal plus 2 LFM signals (with and without noise) CWD of the 3 signals HT of CWD of the 3 signals CWD of the 3 signals in noise (SNR -3dB) HT of CWD of the 3 signals in noise (SNR -3dB) CWD suppresses some cross-terms and preserves horiz/vert cross-terms. Each of the 3 signals in the CWD plot maps to an HT spike. Each of the HT spikes in the noise plot (bottom) is not as ‘tight’ as the HT spikes in the plot w/o noise (top).
- 29. Predetection ESM Sensitivity Enhancement • Wigner-Hough Transform – Approaches Coherent Integration – “Matched” to Chirp and Constant MOP – Separation of Simultaneous Pulses • Provides Parametric information about Frequency and Chirp Rate
- 30. Wigner-Hough Transform Wigner Ville Transform Wx , x (t , f ) x (t 2) x * (t 2) e j 2f d Wigner Hough Transform WH x , x ( f , g ) Wx , x (t , ) ( g t ) dtd Wx , x (t , f g t )dt
- 31. W-H Transform Example • 20 MHz Chirp IF of Cha nne l • 1 usec Pulse Duration 1 0.5 • 200 MHz Sample Rate 0 -0.5 -1 0 0.2 0.4 0.6 0. Time (us e c) P owe r S pe ctra l De ns ity of 20 0 P owe r (dB) -20 -40 -60 0 20 40 60 Fre que ncy (MHz)
- 32. W-H Transform (12 dB SNR) -3 x 10 1 0.9 6000 0.8 5000 0.7 Norma lize d Chirp Ra te 4000 0.6 3000 0.5 2000 0.4 1000 0.3 0 1 0.2 60 -3 0.5 50 0.1 x 10 40 30 0 Norma lize d Chirp Ra te 0 20 20 25 30 35 40 45 Fre que ncy (MHz) Fre que ncy (MHz)
- 33. W-H Transform (0 dB SNR) -3 x 10 1 0.9 4000 0.8 0.7 Norma lize d Chirp Ra te 3000 0.6 2000 0.5 1000 0.4 0.3 0 1 0.2 60 -3 0.5 50 0.1 x 10 40 30 0 Norma lize d Chirp Ra te 0 20 20 25 30 35 40 45 Fre que ncy (MHz) Fre que ncy (MHz)
- 34. Simultaneous Signals • 2 Pulses – Same Center 2 IF of Cha nne l Frequency 1 0 – Same TOA -1 0 0.2 0.4 0.6 0.8 • Pulse 1 20 Time (us e c) P owe r S pe ctra l De ns ity of Cha – 20 Mhz Chirp 0 P owe r (dB) -20 • Pulse 2 -40 -60 0 20 40 60 Fre que ncy (MHz) – Constant RF
- 35. W-H Transform-simultaneous signals -3 x 10 1 0.9 5000 0.8 4000 0.7 Norma lize d Chirp Ra te 3000 0.6 2000 0.5 0.4 1000 0.3 0 1 0.2 60 -3 0.5 50 0.1 x 10 40 30 0 Norma lize d Chirp Ra te 0 20 20 25 30 35 40 45 Fre que ncy (MHz) Fre que ncy (MHz)
- 36. Modern Receivers for Modern Threats • Integration over times on the order of 1-10 ms over bandwidths on the order of 100 MHz. are required to cope with short range FMCW or Phase coded radars expected on the modern battlefield. (BT~10, 000- 100,000) • Fast A/D conversion and DSP are the keys to implementation of these ESM strategies.
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