Get ready for software-defined RADAR

With a big RF transmitter and enough fast computing power, you have the ability to do a lot of different things, as evidenced by a General Electric presentation on "software-defined radar" at the GPU conference this year.

At GTC 13 last year, GE gave a standing-room-only presentation about how it's using RDMA (Remote Direct Memory Access) to drive multi-GPU process performance to new heights. The firm was back this year to talk about new and innovative applications of GPU tech it has cooked up over the past year.

How it works: Simultaneous transmit/receive for a whole load of functions

In its session, Dustin Franklin, GE GPU Applications Engineer guru, gives us an update on how it has been proceeding with RDMA and how it allows the electric company to build large scale, multi-node, products.

U.S. Finishes Wind Turbine Radar Interference Trials

The FAA and other U.S. government agencies have completed the third and final operational field test in a two-year, $8 million program to study the physical and electromagnetic interference between radar systems and wind turbine farms, and to identify mitigation techniques to address this issue.

Data from the third Interagency Field Test and Evaluation of Wind Turbine-Radar (IFT&E), designed to assess near-term mitigation and to help develop long-term mitigation techniques, is being analyzed by Sandia National Laboratories and the Massachusetts Institute of Technology Lincoln Laboratory. The test took place in April.

Interference with radar has been a safety concern for both the FAA and the military, as well as a key roadblock to developers of new wind turbine farms, both in the U.S. and abroad.

Energy needs are accelerating plans for new wind farms, and elevating the priority for finding mitigation measures for radar interference. According to the U.S. Department of Energy (DOE), since 2000 wind power-generation capacity in the U.S. has increased from 5 gigawatts to 60, and could increase to as much as 305 gigawatts by 2030, supplying about 20% of U.S. electricity needs.

Fundamentals of radar signal processing by Mark A. Richards

Source

A signal processing view of strip-mapping synthetic aperture radar

Munson, D.C., Jr.; Visentin, R.L., "A signal processing view of strip-mapping synthetic aperture radar," Acoustics, Speech and Signal Processing, IEEE Transactions on , vol.37, no.12, pp.2131,2147, Dec 1989. doi: 10.1109/29.45556

Abstract: The authors derive the fundamental strip-mapping SAR (synthetic aperture radar) imaging equations from first principles. They show that the resolution mechanism relies on the geometry of the imaging situation rather than on the Doppler effect. Both the airborne and spaceborne cases are considered. Range processing is discussed by presenting an analysis of pulse compression and formulating a mathematical model of he radar return signal. This formulation is used to obtain the airborne SAR model. The authors study the resolution mechanism and derive the signal processing relations needed to produce a high-resolution image. They introduce spotlight-mode SAR and briefly indicate how polar-format spotlight processing can be used in strip-mapping SAR. They discuss a number of current and future research directions in SAR imaging

Reference

Range-Doppler Imaging of Rotating Objects

Walker, Jack L., "Range-Doppler Imaging of Rotating Objects," Aerospace and Electronic Systems, IEEE Transactions on , vol.AES-16, no.1, pp.23,52, Jan. 1980
doi: 10.1109/TAES.1980.308875

Abstract: During the integration time required to obtain fine Dopplerfrequency resolution in a range-Doppler imaging radar, a point on a rotating object may move through several range and Doppler resolution cells and produce a smeared image. This motion can be compensated by storing the appropriately processed return pulse, and the angular coordinates are determined by the angular coordinates of the radar antenna. The resulting stored data represents the three-dimensional Fourier transform of the object reflectivity density, and hence can be processed by an inverse Fourier transformation. Also included is an analysis of the three-dimensional radar/object geometry with separate source and receiver locations. The effects of various system aberrations are investigated and experimental results from a microwave test range which demonstrate the image improvement are presented.

Reference

Statistical analysis of the zero-phase method for aligning noisy high-resolution radar signals

Automatic target recognition using high-range resolution radars is a difficult task. Variations in the distance to the target cause circular shifts of the received signal, and most of the classification algorithms are very sensitive to shifts over the input signal. This fact makes the alignment of each signal prior to any classification stage very important. Here the alignment of noisy signals using the zero phase method is studied. In order to evaluate the performance of the alignment method, a theoretical analysis of the sensitivity to noise of this alignment method is carried out. As a result, an analytical expression that predicts the error of the alignment method is obtained. The validity of this expression is also confirmed by experimental results. A database of high-range resolution radar profiles containing patterns belonging to six different targets has been used, and a comparative study of the sensitivity to noise estimated using the profiles of the database and predicted by the analytical expression is carried out. The results demonstrate that the proposed analytical expression is useful to analyse the sensitivity to noise of the zero-phase alignment method for medium and high signal-to-noise ratio values. - Reference

Discrete frequency-coded radar signal design

A modified simulated annealing algorithm (MSAA) is proposed as combinatorial multivariable optimisation technique to design discrete frequency-coding (DFC) sequence sets with good auto- and cross-correlation properties. The proposed algorithm is a combination of simulated annealing and Hamming scan algorithm. MSAA has global minimum estimation capability of simulated annealing and fast convergence rate of Hamming scan algorithm. Some of the synthesised results are presented, the properties of the sequence sets are shown to be better than the other sequence sets known in the literature. Synthesised DFC sequence sets have properties far better than polyphase sequence sets. The synthesised DFC sequence sets are promising for practical application to netted radar/multiple radar systems. - Reference

Three uncertainty relations for real signals associated with linear canonical transform

Uncertainty principle plays an important role in signal processing, physics and mathematics, and it represents the relations between time spread and frequency spread (or position and velocity). Linear canonical transform (LCT) is one generalisation of Fresnel transform, fractional Fourier transform and others. The LCT has been used in physical optics and signal processing. Three novel results of uncertainty principle in the LCT domains are obtained here, in which one is connected with parameters a and b and the other one is connected with c and d; the last one is connected with the four transformation parameters a, b, c and d. Their physical meanings are given as well. These results disclose the inequalities¿ relations between two spreads, between two group delays and between one spread and one group delay in the LCT domains. It also shows that any one of the three cases can reduce to classical uncertainty principle in time/frequency domain. The effects of time scaling on these results; bounds are also involved. - Reference

Composite spectrogram using multiple Fourier transforms

The authors propose a time-frequency (T-F) analysis method that uses a time- and frequencydependent resolution to represent a signal. The method is based on the idea of splitting the T-F plane into equal-TF-area Heisenberg boxes in some optimal way that closely matches spectral events. Compared with existing methods based on orthogonal decompositions, by lifting the orthogonality constraint, extra freedom is gained in the way the T-F plane can be partitioned, which enables time and frequency adaptation at the same time. A best tiling selection algorithm of quadratic complexity is derived using dynamic programming to find the optimal frame from a family. Experiments show the advantage of this more flexible representation. - Reference

Coupled Contributions in the Doppler Radar Spectrum Width Equation

Contrary to accepted usage, the second central moment of the Doppler spectrum is not the sum of the second central moments of individual spectral broadening mechanisms. A rigorous theoretical derivation of the spectrum width observed with short dwell times reveals that the sum cannot strictly be taken for the variances associated with various spectral broadening mechanisms and that an added-term coupling shear with turbulence is needed. Furthermore, shear and antenna rotation are coupled. The theoretical expressions derived herein apply to radars with fixed or scanning beams.- Reference

Clutter Suppression for Staggered PRT Waveforms

This paper presents a clutter suppression methodology for staggered pulse repetition time (PRT) observations. It is shown that spectral moments of precipitation echoes can be accurately estimated even in cases where clutter-to-signal ratios are high by using a parametric time domain method (PTDM).

Based on radar signal simulations, the accuracy of the proposed method is evaluated for various observation conditions. The performance of PTDM is demonstrated by the implementation of the staggered PRT at the Colorado State University–University of Chicago–Illinois State Water Survey (CSU–CHILL). Based on this study, it is found that the accuracy of the retrieval is comparable to the current state of the art methods applied to the uniformly sampled observations and that the estimated velocity is unbiased for the complete Nyquist range.- Reference

Annotated bibliography - "Pulse compression in Radars"

Listing are chronological

• Woodward, P.M., Probability and Information Theory, With Applications to Radar, New York: McGraw-Hill Book Co. (1955).
  Fundamentals of resolution theory and ambiguity functions, including linear-FM pulse.
• Cook, C.E., "Modification of Pulse-Compression Waveforms," Proc. NEC 14, 1958, pp 1058-67.
  Basic paper on linear FM pulse compression technique.
• Cook, C.E., "Pulse Compression-Key to More Efficient Radar Transmission," Proc IRE 48, No 3, Mar. 60, pp 310-316.
  Basic paper on linear-FM pulse compression technique. Reprint Paper No. 1 in Source.
• Westerfield, E.C., Prager, R.H. and Stewart, J.L. "Processing Gains Against Reverberation (Clutter) Using Matched Filters," IRE Trans IT-6, No 3, Jun 1960, pp 342-349.
  Use of Woodward ambiguity function to calculate signal-to-clutter ratio in radar and sonar systems.
• Klauder, J.R. et. al., "The Theory and Design of Chirp Radars," BSTJ 39, No 4, Jul 1960, pp 745-808.
  Basic paper on linear-FM pulse compression theory, sidelobe reduction, and error effects. Reprint Paper No. 2 in Source.
• Klauder, J.R., "The Design of Radar Signals Having Both High Range Resolution and High Velocity Resolution," BSTJ 39, No 4, Jul 1960, pp 809-820.
  Derivation of waveform having circularly symmetric ambiguity function. Required amplitude modulation precludes efficient transmission.
• Key, F.L., Fowle, E.N. and Haggarty, R.D., "A Method of Designing Signals of Large Time-Bandwidth Product," IRE Conv Record, 1961, Pt. 4, pp 146-154.
  Design of signals for which envelope shape and autocorrelation function are separately specified.
• Ramp, H.O. and Wingrove, E.R., "Principles of Pulse Compression," IRE Trans M/L-5, No 2, Apr 1961, pp 109-116.
  Basic paper on linear-FM pulse compression principles and applications. Reprint Paper No. 3 in Source.
• Cook, C.E., "General Matched-Filter Analysis of Linear FM Pulse Compression," Proc IRE 49, No 4, Apr 1961, p 831.
  Considers effect of Doppler shift on output waveform of filter matched to linear-FM signal, including bandwidth restriction.
• DiFranco, J., "Closed-Form Solution for the Output of a Finite-Bandwidth Pulse-Compression Filter," Proc IRE 49, No 6, Jun 1961, pp 1086-87.
  Evaluation of integrals leading to output waveform in band limited cases.
• DiFranco, J.V. and Rubin, W.L., "An Interpretation of 'Paired Echo Theory' for Time-Domain Distortion in Pulsed Systems and an Extension to the Radar 'Uncertainty Function'," Proc IRE 49, No 9, Sep 1961, pp 1432-1433.
  Description of spurious outputs caused by frequency-domain and time-domain distortions.
• Reed, J., "Long-Line Effect in Pulse Compression Radar," Microwave Journal 4, No 9, Sep 1961, pp 99-100.
  Effect of transmission line mismatch on phase-vs-frequency response of radar system. Reprint Paper No. 4 in Source.
• Ramp, H.О. and Wingrove, E.R., "Performance Degradation of Linear FM Pulse Compression," Proc IRE 49, No 11, Nov 1961, p 1693.
  Analysis of output waveform of Doppler shifted signal, including second-order Doppler terms which can be important for large time-bandwidth product.
• Cook, C.E., "Effects of Phase-Modulation Errors on Radar Pulse Compression Signals," IRE Conv Record, 1962, Pt 4, pp 174-184.
  Analysis and experimental data on effect on sinusoidal phase errors on output waveform.
• Thor, R.C., "A Large Time-Bandwidth Product Pulse Compression Technique," IRE Trans MIL-6, No 2, Apr 1962, pp 169-173.
  Use of logarithmic, rather than linear, frequency modulation is shown to permit use of greater time-bandwidth products on targets with large radial velocity. Reprint Paper No. 5 in Source.
• DiFranco, J.V. and Rubin, W.L., "Analysis of Signal Processing Distortion in Radar Systems," IRE Trans MIL-6, No 2, Apr 1962, pp 219-227.
  Describes effects of phase and amplitude distortion on ambiguity function shape and sidelobe levels.
• Cook, C.E. and Heiss, W.H., "Linear FM Pulse Compression Doppler Distortion Effects," Proc IRE 50, No 6, Jun 1962, pp 1535-1536.
  Further discussion of dispersive Doppler effect and different viewpoints of Cook (1961) and Ramp and Wingrove (1961).
• Fryberger, D., "On the Use of Pulse Compression for the Enhancement of Radar Echoes from Diffuse Targets," Proc IRE 50, No 9, Sep 1962, pp 1993-1994.
  Compares effect of pulse compression on SNR and resolution for diffuse and discrete targets.
• Rubin, W.L. and DiFranco, J.V., "The Effects of Doppler Dispersion on Matched Filter Performance," Proc IRE 50, No 10, Oct 1962, pp 2127-2128.
  Expressions are derived for the difference between simple frequency shift and Doppler shift with dispersion, and it is shown that this difference is negligible for time-bandwidth products less than 1000.
• Fowle, E.N. el. al., "A Pulse Compression System Employing a Linear FM Gaussian Signal." Proc IEEE 51, No 2, Feb 1963, pp 304-312.
  Design and equipment considerations for low-sidelobe pulse compression systems using approximations to Gaussian weighting.
• Cook, C.E., "Pulse-Compression Paired-Echo Experiments," Proc IEEE 51, No 2, Feb 63, pp 383-384.
  Experimental verification of paired-echo response caused by sinusoidal phase errors in pulse compression signal.
• Temes, C.L. et. al. "Pulse Compression System for a Down-Range Tracker," IEEE Conv Rec 1963, Pt 8, pp 71-81.
  Description of 4 MHz 2 ms pulse compression waveform for 425 MHz instrumentation radar.
• Cook, C.E., "Transmitter Phase Modulation and Pulse Compression Waveform Distortion," Microwave Journal 6, No 5, May 1963, pp 63-69.
  Analysis of paired-echo effect of sinusoidal phase error, and sidelobe increase caused by localized phase error in chirp signal. Reprint Paper No. 6 in Source.
• Minis, W.B., "The Detection of Chirped Radar Signals by Means of Electron Spin Echoes," Proc IEEE 51, No 8, Aug 1963, pp 1127-1134.
  Theory and experimental results using compression filter based on paramagnetic resonance line at 6.7 GHz.
• Bernfeld, M., "Pulse Compression Techniques," Proc IEEE 51, No 9, Sep 63, p 1261.
  Comparison of systems using series and parallel dispersive elements to generate large time-bandwidth products.
• Lurin, E.S., "Digital Pulse Compression Using Polyphase Codes," Proc IEEE 51, No 9, Sep 63, pp 1262-1263.
  Implementation and ambiguity function of digital equivalent of linear and triangular-FM pulse compression.
• Fowle, F.N., "The Design of FM Pulse Compression Signals," IEEE Trans IT-10, No 1, Jan 1964, pp 61-67.
  Discusses design of waveform having arbitrary transmitted envelope, to produce given autocorrelation function.
• Cook, C.E. and Paolillo, J., "A Pulse Compression Predistortion Function for Efficient Sidelobe Reduction in a High-Power Radar," Proc IEEE 52, No 4, Apr 1964, pp 377-89.
  Describes use of increased sweep rate on leading and trailing edges of pulse to reduce paired-echo sidelobes.
• Cook, C.E., "A Class of Nonlinear FM Pulse Compression Signals," Proc IEEE 52, No 11, Nov 1964, pp 1369-1371.
  Analysis of nonlinear chirp to achieve sidelobe reduction, showing sensitivity to Doppler shift.
• Bernfeld, M. et. al., "Matched Filtering, Pulse Compression and Waveform Design," Microwave Journal, Oct, Nov, Dec 1964; Jan 1965, pp 57-64, 81-90, 70-76, 73-81.
  Thorough discussion and analysis of linear and nonlinear FM and discrete code waveforms and their ambiguity functions. Reprint Paper No. 7 in Source.
• Bogotch, S.E. and Cook, C.E., "The Effect of Limiting on the Detectability of Partially Time Coincident Pulse Compression Signals," IEEE Trans M/L-9, No 1, Jan 1965, pp 17-24.
  Theory and experimental results on suppression of small signals by overlap of expanded pulse from large, adjacent signal which would be resolvable except for receiver limiting. Reprint Paper No. 8 in Source.
• Peebles, P.Z. and Stevens, G.H., "A Technique for the Generation of Highly Linear FM Pulse Radar Signals," IEEE Trans M/L-9, No 1, Jan 1965, pp 32-38.
  A method is described for generating a staircase FM waveform, closely approximating linear sweep with very high accuracy.
• Rihaczek, A.W., "Radar Signal Design for Target Resolution," Proc IEEE 53, No 2, Feb 1965, pp 116-128.
  Relationships between resolution and measurement uncertainty are explored for different signals and clutter environments.
• Rihaczek, A.W., "Range Accuracy of Chirp Signals," Proc IEEE 53, No 4, Apr 1965, pp 412-13.
  It is shown that the diagonal ambiguity of chirp signals does not lead to range uncertainty on targets of unknown Doppler if the range reading is interpreted as applying at a time displaced from the actual echo time. Reprint Paper No. 9 in Source.
• Jacob, J.S., "Graphical Comparison of a Doppler-Shift Advantage for Three Pulse-Compression Techniques," Proc 9th Natl Conv on Military Electr, IELE, Wash, D.C., 1965, pp 382-387.
  Degradation in SNR with Doppler shift is compared for three waveforms, and linear FM is shown to be affected less than phase-coded or frequency-stepped waveforms.
• Ward, M.X., ''Matched Scan Rate Pulse-Compression Analysis," Proc IEEE 54, No 4, Apr 1966, pp 707-708.
  Derives output waveform for compression filter with arbitrary impulse response duration, showing approach to (sin x)/x shape for long durations.
• Rihaczek, A.W., "Doppler-Tolerant Signal Waveforms," Proc IEEE 54, No 6, Jun 1966, pp 849-857.
  Discussion of non-linear FM modulations and pulse trains for which Doppler distortions can be ignored.
• Hollis, E.E., "Comparison of Combined Barker Codes for Coded Radar Use," IEEE Trans AES-3, No 1, Jan 1967, pp 141-143.
  Sidelobe levels are determined for sequences of four 13-bit Barker Codes and thirteen 4-bit codes, showing maximum amplitude 13/52 times main lobe.
• Lipman, M.A. "A Useful Property of the Generalized Chirp Signal Ambiguity Function," Proc IEEE 55, No 7, Jul 1967, pp 1241-1242.
  Ambiguity function generalized to include mismatched sweep rate as well as delay and Doppler shift.
• Cook, C.E. and Bernfeld, M. Radar Signals, New York: Academic Press, 1967.
  Basic text on pulse compression principles and implementation.
• Kibbler, G.O.T.H., "The CLFM: a Method of Generating Linear Frequency-Coded Radar Pulses," IEEE Trans AES-4, No 3, May 68, pp 385-391.
  Describes coherent linear frequency modulator used in active generation of chirp signals and in conversion of received signals to constant frequency.
• Mitchell, R.L. and Rihaczek, A.W., "Matched-Filter Responses of the Linear FM Waveform," IEEE Trans AES-4, No 3, May 1968, pp 417-432.
  Equations and three-dimensional plots of ambiguity functions with and without weighting and mismatch.
• Rihaczek, A.W., and Mitchell, R.L., "Design of Zigzag FM Signals," IEEE Tram AES-4, No 5, Sep 1968, pp 680-692.
  Presents three-dimensional plots of ambiguity functions of simple and multiple-segment zigzag FM waveforms.
• Haggarty, R.D., Hart, L.A. and O'Leary, G.C, "A 10.000 to 1 Pulse Compression Filter Using a Tapped Delay Line Linear Filter Synthesis Technique," IEEE EASCON Rec, 1968, pp 306-314.
  Synthesis procedure and experimental results on delay-line filters for large time-bandwidth product pulse compression and other applications. Reprint Paper No. 10 in Source.
• Belknap, D.J., "An Experimental Measurement of the Detection Capability of a Linear FM Pulse Compression System," IEEE EASCON Rec, 1968, pp 315-318.
  Detection performance of 1000:1 pulse compression system is compared with ideal matched filter and with Doppler filter bank. Results are within a fraction of a dB of the matched filter.
• Ruttenberg, K. and Chanzit, L., "High Range Resolution by Means of Pulse-To-Pulse Frequency Shifting," IEEE EASCON Record, 1968, pp 47-51.
  Method of obtaining resolution in system using agile magnetron rather than intrapulse FM. Reprint Paper No. 11 in Source.
• Leith, E.N., "Optical Processing Techniques for Simultaneous Pulse Compression and Beamsharpening," IEEE Trans AES-4, No 6, Nov 1968, pp 879-885.
  Combined processing for synthetic aperture resolution and pulse compression, using two-dimensional optical filter.
• Bechtel, M.E., "Generalized Paired-Echo Analysis for Band-pass Systems," Proc IEEE 57, No 2, Feb 1969, pp 204-205.
  Description of phase and amplitude distortion terms in bandpass systems in terms of advanced and delayed replicas of ideal signal.
• Palmieri, C.A. and Cook, C.E., "The Ambiguity Properties of Multiple-Segment Linear FM Signals," Proc IEEE 57, No 7, Jul 1969, pp 1323-1325.
  Approximate analysis of mainlobe and near-sidelobe response of multiple-segment FM waveforms.
• Vannicola, V.C., "Range Dependent Waveform of an Active Weighted Pulse Compression Receiver," IEEE Trans AES-5, No 5, Sep 1969, pp 847-864.
  Output waveforms for pulse compression systems in which the signal is time weighted by a function not exactly centered on the received signal. Reprint Paper No. 12 in Source.
• Nathanson, F.E., Radar Design Principles, New York, McGraw-Hill, 1969.
  Text covering radar clutter and resolution requirements, with chapters devoted to phase coding and to linear-FM processing techniques.
• Rihaczek, A.W., Principles of High-Resolution Radar, New York: McGraw-Hill, 1969.
  Basic text on waveform design and results in resolution, detection and measurement in clutter.
• Campbell, B.D., "High-Resolution, Radar Coherent Linear FM Microwave Source," IEEE Trans AES-6, No 1, Jan 1970, pp 62-72.
  Design of BWO generator for 16 Hz FM Sweep at S-band.
• Millett, R.E., "A Matched-Filter Pulse-Compression System Using a Nonlinear FM Waveform," IEEE Trans AES-6, No 1, Jan 1970, pp 73-78.
  Design and test data on low-sidelobe pulse compression waveform having 0.1 dB mismatch loss. Reprint Paper No 13 in Source.
• Cohen, S.A., "Generalized Response of a Linear FM Pulse Compression Matched Filter," IEEE Trans AES-6, No 5, Sep 1970, pp 708-712.
  Curves are derived which show losses in peak output caused by mismatch of pulse width, sweep rate and center frequency.
• Caputi, W.J., Jr., "Stretch: A Time-Transformation Technique," IEEE Trans AES-7, No 2, Mar 1971, pp 269-278.
  Technique for very high resolution with relatively simple processor covering a limited range window. Reprint Paper No. 14 in Source.
• Hartt, J.K. and Sheats, L.F., "Application of Pipeline FFT Technology in Radar Signal and Data Processing," IEEE EASCON Record 1971, pp 216-221.
  Pipeline FFT processors for pulse compression and Doppler filtering are described. Reprint Paper No. 15 in Source.
• Halpern, H.M. and Perry, R.P. "Digital Matched Fitters Using Fast Fourier Transforms," IEEE EASCON Record 1971, pp 222-230.
  A 10-MHz bandwidth digital filter, suitable for high-resolution pulse compression, is described. Effects of different word lengths for signal and reference waveforms are explored by simulation. Reprint Paper No. 16 in Source.
• Woerrlein, N.H., "Spurious Target Generation Due to Hard Limiting in Pulse Compression Radars," IEEE Trans AES-7, No 6, Nov 1971, pp 1170-1178.
  Method and results for calculating spurious outputs caused by hard limiting of three overlapping signals, using phase-coded waveform.
• Rihaczek, A.W., "Radar Waveform Selection-A Simplified Approach," IEEE Trans AES-7, No 6, Nov 1971, pp 1078-1086.
  Waveforms are divided into four classes, each with distinct resolution properties, permitting a systematic approach to waveform selection. Reprint Paper No 17 in Source.
• Jones, W.S., Kempf, R.A. and Hartmann, C.S., "Practical Surface Wave Chirp Fillers for Modern Radar Systems," Microwave Journal, May 1972.
  Design, application and performance of surface acoustic wave filters for 8 MHz x 12.5 usec and 2 MHz x 25 usec pulse compression. Reprint Paper No 18 in Source.
• Ackroyd, M.H. and Ghani, F., "Optimum Mismatched Filters for Sidelobe Suppression," IEEE Trans AES-9, No 2, Mar 1973, pp 214-218.
  At some expense in complexity and small loss in SNR, time sidelobes can he reduced without amplitude weighting on transmit.
• Powell, Т.Н., Jr. and Sinsky, A.I., "A Time Sidelobe Reduction Technique for Small Time-Bandwidth Chirp," IEEE Trans AES-10, No 3, May 1974, pp 390-392.
  Digital filter design to compensate for effect of Fresnel ripples in spectrum of chirp signal.
• Hollan, M.G. and Claiborne, L.T., "Practical Surface Acoustic Wave Devices," Proc IEEE 62, No 5, May 1974, pp 582-611.
  Tutorial discussion of SAW devices and their application, with extensive bibliography.
• Fitzgerald, R.J., "Effects of Range-Doppler Coupling on Chirp Radar Tracking Accuracy," IEEE Trans AES-10, No 4, Jul 1974, pp 528-532.
  Describes interaction of chirp range-Doppler coupling with truncation error of GHK filler, such that positive chirp slope leads to reduced error of filtered data.
• Caputi, W.J., "Stabilized Linear FM Generator," IEEE Trans, AES-9, No 5, Sep 1973, pp 570-578.
  Closed-loop technique for controlling slope of linear frequency sweep generator, as applied to 240 MHz x 120 usec active pulse-compression waveform generator.

Source: Radars. Vol 3. Pulse Compression. By David K. Barton. Dedham: Artech House, Inc., 1975.

Maximum Position Alignment Method for Noisy High-Resolution Radar Target Classification

In this paper, the alignment of noisy high-resolution radar signals using the maximum position method is studied. The relationship between the shift estimation and the signal-to-noise ratio is considered. As a result, two analytical expressions are obtained that approximate the root-mean-square error of the difference in the shift estimation with and without noise. These two expressions allow us to improve the understanding of the sensitivity to noise of the Maximum Position alignment method. - Reference

Predicted Detection Performance of MIMO Radar

It has been shown that multiple-input multiple-output (MIMO) radar systems can improve target detection performance significantly by exploiting the spatial diversity gain. We introduce the system model in which the radar target is composed of a finite number of small scatterers and derive the formula to evaluate the theoretical probability of detection for the system having an arbitrary array-target configuration. The results can be used to predict the detection performance of the actual MIMO radar without time-consuming simulations. - Reference

Simulating Range Oversampled Doppler Radar Profiles of Inhomogeneous Targets

A new technique for generating range oversampled profiles of Doppler radar signals that have been backscattered by distributed targets is presented in this paper. The technique was developed for spaceborne cloud radars, but it can just as well be used for ground-based precipitation or wind-profiling radars. The technique is more versatile than the traditional inverse FFT technique and faster than the individual hydrometeor simulation (Monte Carlo) technique. Doppler radar signals from backscattering hydrometeors are essentially correlated stochastic variables. The technique uses an accurate description of covariances between voltages measured for different pulses and at different positions (range gates) along a profile. A matrix formalism is developed to subsequently transform uncorrelated Gaussian noise into correlated receiver voltages with the appropriate covariances. In particular, the new technique deals with target variability in a physically consistent manner, accounting for the effects of inhomogeneity both within the instantaneous field of view and between subsequent pulses. The new technique is showcased with examples of simulated 95-GHz Doppler radar observations by the Earth Clouds, Aerosols and Radiation Explorer (EarthCARE) space mission. - Reference

A Technique for the Automatic Detection of Insect Clutter in Cloud Radar Returns

The U.S. Department of Energy Atmospheric Radiation Measurement (ARM) Program operates 35-GHz millimeter-wavelength cloud radars (MMCRs) in several climatologically distinct regions. The MMCRs, which are centerpiece instruments for the observation of clouds and precipitation, provide continuous, vertically resolved information on all hydrometeors above the ARM Climate Research Facilities (ACRF). However, their ability to observe clouds in the lowest 2–3 km of the atmosphere is often obscured by the presence of strong echoes from insects, especially during the warm months at the continental midlatitude Southern Great Plains (SGP) ACRF. Here, a new automated technique for the detection and elimination of insect-contaminated echoes from the MMCR observations is presented. The technique is based on recorded MMCR Doppler spectra, a feature extractor that conditions insect spectral signatures, and the use of a neural network algorithm for the generation of an insect (clutter) mask. The technique exhibits significant skill in the identification of insect radar returns (more than 92% of insect-induced returns are identified) when the sole input to the classifier is the MMCR Doppler spectrum. The addition of circular polarization observations by the MMCR and ceilometer cloud-base measurements further improve the performance of the technique and form an even more reliable method for the removal of insect radar echoes at the ARM site. Recently, a 94-GHz Doppler polarimetric radar was installed next to the MMCR at the ACRF SGP site. Observations by both radars are used to evaluate the potential of the 94-GHz radar as being insect free and to show that dual wavelength radar reflectivity measurements can be used to identify insect radar returns. - Reference

Constant false-alarm rate algorithm based on test cell information

A new constant false-alarm rate (CFAR) detection algorithm, designated as switching CFAR (S-CFAR), is proposed and analysed. The S-CFAR algorithm selects CFAR reference samples using the magnitude of the sample in the cell under test, which is an information that has not been exploited in any other existing CFAR detectors. S-CFAR closed-form analysis is presented, and comparisons with other representative CFAR algorithms are given. An S-CFAR detector can be tuned such that it has a small CFAR loss when operating on a homogeneous background while achieving improved robustness in the presence of interfering targets and clutter power transition. The S-CFAR detector is also simple to design and implement since no sample ordering is required. - Reference

Fundamental resolution limits of closely spaced random signals

Fundamental limitations on estimation accuracy are well known and include a variety of lower bounds including the celebrated Cramer-Rao lower bound. However, similar theoretical limitations on resolution have not yet been presented. The authors exploit results from detection theory for deriving fundamental limitations on resolution. In this correspondence the authors discuss the case of zero mean random Gaussian signals with a general and predefined covariance matrix observed with additive white Gaussian noise. The results are general and are not based on any specific resolution technique and therefore hold for any method and for any probability of successful resolution. The resolution limit is a simple expression of the observation interval, the pre-specified resolution success probability and the second derivative of the covariance matrix. As an example, the authors discuss the bearing resolution of two emitters with closely spaced direction of arrival, impinging on an array of sensors. The theoretical limits are compared with empirical performance of the model order selection criteria known as the Akaike information criterion and the minimum description length. - Reference

A Two-Dimensional Spectrum Model for General Bistatic SAR

This paper derives a 2-D spectrum model for general bistatic synthetic aperture radar (SAR). By introducing some new parameters such as equivalent monostatic parameters, bistatic factor, and weighted-equivalent range, the 2-D spectrum of general bistatic SAR can be expressed in the form of monostatic SAR even when the transmitter and receiver move along unparallel trajectories with different velocities. The result formulates bistatic SAR into an equivalent monostatic SAR model and would be useful for developing efficient bistatic SAR algorithms in frequency-domain or hybrid-domain processing. Simulation results are given to validate the performance of the model. For special bistatic SAR configurations, the model can be simplified. Compared to other similar models, the proposed model is clearer and much more concise. - Reference

Information Theory-Based Approach for Contrast Analysis in Polarimetric and/or Interferometric SAR Images

We propose a new approach for evaluating the contribution of the different channels of polarimetric and interferometric synthetic aperture radar (PolInSAR) images. For that purpose, we demonstrate that the Bhattacharyya distance between the probability density functions of neighboring regions in the image provides an efficient scalar contrast measure. We show that the analysis of this contrast measure allows one to precisely characterize the contribution of each channel for different system configurations, including intensity, polarimetric, and interferometric images. We illustrate this approach using a real synthetic aperture radar image to compare several polarimetric system architectures. Since PolInSAR imaging configurations can correspond to complex and expensive systems, the proposed method can be helpful in system imaging optimization. - Reference