Abstract: A Two-Stage Hybrid algorithm offers significant improvement in the false alarm rate and detection performance of Space-Time Adaptive Processing in non-homogeneous environments for both radar and digital communications. The first stage analyzes data from a range cell of interest by direct data domain processing, suppressing discrete interferers within the range cell of interest. The second stage implements a purely statistical STAP algorithm, preferably an enhanced version of the Joint-Domain Localized (“JDL”) statistical algorithm. For radar this second stage estimates the interference within the range cell of interest from the surrounding range cells. For a communications system, the second stage estimates the covariance matrix of the interference from the entire data block. For both radar and communications, an adaptive filter that suppresses the interference is generated from the estimate by second-order statistics.

Abstract: Stealthcraft are detected by illuminating backgrounds with narrow radar or sonar beams and monitoring this background illumination for the changes that result when these beams are absorbed by such targets, and are ranged by triangulation using two such beams.

Abstract: A process for correcting data from a three dimensional bistatic synthetic aperture radar system to eliminate distortions and resolution limitations due to the relative positions and motions of the radar transmitter and receiver with respect to a target.

Abstract: In a method for the probabilistic estimation of measurements, based on a measurement signal in which an interference signal is superimposed on the value to be measured, the measurement signal is sampled at specified chronological intervals. A defined measurement range associated with the value to be measured is divided into discrete values and a model is formed of a process on which the measurement signal is based with discrete states that correspond to the discrete values of the measurement range. In the model, a probability value of the occurrence of each state is assigned for each sampling time, and the value to be measured is determined on the basis of the probability value of at least one state in this model. In addition, for each state of the model at a sampling time, a probability for the state to remain in its current state is determined, as well as a probability for the state to change to another state by the next sampling time.

Abstract: A coherent, frequency agile pulse radar system in which each transmitted pulse is made up of subpulse pairs having frequencies of &ohgr;o±&Dgr;i forces a jammer to broadband jam the system in order to ensure jamming the actual operating frequency of the system. On reception, a separate receiver channel is utilized for the detection of each subpulse frequency. Within the processing system, the signal return for a subpulse having a frequency of &ohgr;o+&Dgr;l is multipled times the signal return for the subpulse having a frequency of &ohgr;o−&Dgr;l to provide a combined signal which is free of the offset frequencies. This combined signal is a standard coherent frequency agile pulse doppler radar signal with the exception that the carrier frequency and the doppler frequency are both doubled. Moving target indicating or doppler processing may be used.

Abstract: In a phase unwrapping and correction system, phase wrapped data is unwrapped with an unwrapping algorithm to obtain unwrapped image data. The unwrapped image data is further processed to correct the unwrapped image data by dividing the image represented by the unwrapped image data into regions defining boundaries corresponding to inconsistencies in the image data. The regions are then corrected by comparing them with one another and adjusting the multiples of 2.pi. assigned to each region to minimize discontinuities between the regions.

Abstract: A process for modelling of ground clutter received by a radar, starting from a meshed numerical terrain model, including identifying cells from the meshed numerical terrain model which comprise elements having a height greater than a resolution of the model; determining, for relevant cells, an average height of the elements; sectioning the relevant cells into height-wise slices; and calculating power backscattered by each of the relevant cells by representing contents thereof with elementary reflectors distributed over an entire height thereof as a function of adjoining cells and a profile of terrain situated between the radar and a relevant cell.

Abstract: A method for rejecting system-to-system interference in a FLR system in which sampled data obtained from each channel of the FLR receiver is analyzed to recognize transient data due to interference with another FLR system and bounded in the time domain. The bounded data set is deleted and replaced with a new data set determined by interpolation. The transient data is recognized when the variance of a sliding window of samples exceeds a variance threshold. The method removes transient pulses with minimal distortion of the raw data, and the impact on system complexity and cost is minimal when the system already includes digital signal processing capability for other purposes.

Abstract: A Fast Fourier Transformation (FFT) processing is disclosed that measures FFT output phase standard deviation over a number of consecutive FFT runs. The system corrects FFT output phase in an organized fashion for all potential signal filter offset positions while measuring changes in phase standard deviation, and selects the filter offset where the minimum standard deviation occurs. The system utilizes pseudo coherent integration to enhance traditional integration, where the pseudo coherent integration locates the mean phase shift within the number of FFTs integrated, and corrects all FFT runs by this mean shift value. The integration multiplies the magnitude of each FFT filter output by the cosine and sums all FFTs in the integration period for the respective filter.

Abstract: Synthesized multi-channel data is provided based on real world single channel data, thereby yielding data with high fidelity that can be used to test multi-channel equipment and processing techniques. Simulated data representing time dependent characteristics of moving targets can be integrated with the synthesized multi-channel data. In one embodiment a multi-channel data generator (20) includes a real radar data module (30), a computer simulated radar data module (40) and a composite radar data module (50). The real radar data module (30) generates synthesized multi-channel background data (38) based on real world single channel radar data (32). The computer simulated radar data module (40) includes a temporal signal model (42) and a radar signal simulator (44) for generating multi-channel time dependent data (46).

Abstract: A ranging device is disclosed that monitors for changes in a scene of interest. The ranging device includes a transmitter that sends pulses into the scene, a receiver that generates pulse samples in response to pulse returned from the scene, and a target discriminator that analyzes the pulse samples. The target discriminator detects targets entering the scene, targets leaving the scene, and targets moving in the scene through the use of at least one non-averaging statistical characteristic of the pulse samples. The target discriminator may generate short term and long term high order statistical samples in response to the pulse samples as well as detector samples consisting of the ratio of high order statistical samples. The detector samples are highly indicative of the presence or absence of a target in the scene.

Abstract: At a transmitting end, first and second dipole antennas are crossed each other by right angles and are arranged in a plane perpendicular to a propagating direction of radio wave. In first and second balanced modulators, a carrier signal is modulated with respective modulation signals having a phase difference of 90.degree. to produce balanced-modulated signals, which are then supplied to the first and second dipole antennas, respectively. Then a plane of polarization of a composite vector of radio waves transmitted by the dipole antennas is rotated at a frequency of the modulation signals, said frequency being higher than a fading frequency. The modulation signals are controlled by a state of a digital signal to be transmitted. At a receiving end, the digital signal is reproduced by receiving the transmitted radio wave by a conventional single side band receiver.

Abstract: A process and a system for selecting a pulse repetition frequency that causes clutter pulse repetition frequency lines from the negative carrier frequency and from the clutter harmonic frequencies to lay on top of clutter pulse repetition frequency lines from the positive carrier frequency. A pulsed Doppler radar receiver of the system has one or more channels each comprising of a radio frequency input section for receiving a radio frequency carrier. Following the radio frequency input section are one or more serially arranged intermediate frequency sections that terminate in a last intermediate frequency section. The last intermediate frequency section is followed by analog-to-digital conversion and down-conversion to baseband in-phase and quadrature channels. In-phase and quadrature data from the in-phase and quadrature channels is processible by a computational system to detect and track a target in the presence of clutter.

Abstract: A transceiver system comprises transceivers and a controller in communication with the transceivers. Each of the transceivers comprises an emitter, a receiver operatively connected to the emitter, a primary data path operatively connected to the receiver, a secondary data path operatively connected to the receiver, a statistical unit operatively connected to the secondary data path and the controller and a display device operatively connected to the primary data path.

Abstract: A duty dithering method for use with electronic support measures and radar warning receivers, and the like, that provides for improved probability of intercept at low utilization levels. The electronic support measures (ESM) system and radar warning receiver are controlled by a multi-system sensor manager having an ESM scheduler. In accordance with the present method, a maximum duty cycle is chosen for the ESM system. The chosen duty cycle is allocated to the ESM system each frame by the ESM scheduler. At the beginning of each frame, the ESM scheduler picks a random offset and subtracts it from the maximum duty to compute an ESM duty for that frame. The ESM scheduler commands data collections based on the computed duty for that frame. This step is repeated each frame.

Abstract: A system and method of processing data in a sensor system which receives signal returns from pulsed coherent transmitted signals which are transmitted at a pulse repetition rate and with a pulse repetition interval (PRI). The method includes providing range-filtered data in response to the received signal returns; formatting successive sets of data received during a post detection integration (PDI) interval into a plurality of overlapping coherent processing interval (CPI) data sequences; performing FFT processing on the overlapping CPI data sequences to provide transformed data sequences; performing range-sample CPI processing on the transformed data sequences; and performing noncoherent integration (NCI) processing on output data from the range-sample CPI processed data sequences over a range trajectory in accordance with hypothesized radar-target range rate to provide noncoherent gain-enhanced output data.

Abstract: A processing technique suitable for use with a search radar system which minimizes the false detection of targets. Rather than rely on a predetermined target trajectory, such as a straight line trajectory in range time space, the processing technique in accordance with the present invention is not based on a target dynamics model. The system in accordance with the present invention relies on past detections and assigns a confidence level to detections which are in the wake of a previous detection. A wake function is used to determine the amount by which each detection recursively accrues confidence based on a limited record of past detections. A detection is declared when the confidence level exceeds a predetermined threshold. As detections are encountered in range time space, such detections are used to form wakes based on the wake function which are used to assign confidence levels for future detections.

Abstract: Stealthcraft are detected by illuminating backgrounds with narrow radar or sonar beams and monitoring this background illumination for the changes that result when these beams are absorbed by such targets, and are ranged by triangulation using two such beams.

Abstract: A synthetic aperture radar (SAR) which operates at UHF frequencies and which includes a two element antenna. The SAR generates a null in the backlobe of the antenna pattern at the location of a target which is steered rather than trying to obtain directivity in the mainlobe. Both analog and digital implementations are provided. In the analog approach, required phase shifts are performed at a frequency higher than the RF output frequency and the receive and transmit nulls are steered separately to increase the width of the null so as to allow for wider SAR swaths. The digital implementation involves steering the null only on receive and multiplying fast time samples by a complex phase correction similar to that used in the analog approach to form the beam. The phase correction is also performed prior to range resolution which employs "stretch" processing, so as to achieve high range resolution.

Abstract: An along-track interferometric SAR (Synthetic Aperture Radar) of the present invention includes a single SAR line and observes a target only once. SAR data derived from a single observation are subjected to look division in order to reproduce two SAR images deviated in time from each other. Interference processing is executed with the two SAR images in order to determine a phase difference. The phase difference is converted to the velocity of the target. This can be done without resorting to any additional hardware.

Abstract: A digitally-controlled pulse shaper (DCPS) is provided which precisely controls the shape of the leading and trailing edges of a transmit pulse in a radar wind profiler, or pulsed-radar. In the case of pulse coding, where phase transitions are used to segment an otherwise longer pulse, the intra-pulse phase transitions are also shaped.

Abstract: A signal processing system applies space-time adaptive processing ("STAP") to an airborne surveillance Doppler radar comprised of a single-channel, electronically scanned antenna. The STAP substantially improves signal-to-interference-plus-noise ratio ("SINR") by synthetically creating angular degrees of freedom, thereby improving the detection of weak targets.

Abstract: An inertial navigation system (INS) and a monopulse radar system are mounted on a body. The inertial navigation system outputs at least a velocity of the body. Either a synthetic aperture radar (SAR) map or doppler beam sharpening (DBS) map is created using the outputs of the monopulse radar system. The monopulse radar system outputs at least a summation output, an azimuth difference and an elevation difference associated with an object detected in either the SAR or DBS map. The position processor of the system and method of the present invention, however, only inputs the summation output and one of the azimuth difference and election difference. The position processor determines the other of the azimuth difference and the elevation difference by converting the velocity output by the INS into a doppler angle .theta. (the angle between the velocity, a vector, and a line connecting the object and the body) and determining either the azimuth difference or the elevation difference from the doppler angle .theta..

Abstract: Disclosed is a new alternative method for the phase unwrapping of the interferogram of two SAR (Synthetic Aperture Radar) images of the same area. This new method uses an iterative approach to the phase unwrapping problem by applying local circular or elliptical masks centered on the phase residues. A phase unwrapping error is detected automatically during the unwrapping process by comparing each unwrapped value with neighboring unwrapped values. This new method for phase unwrapping significantly improves the quality of unwrapped phase maps. This will allow extraction of quantitative information such as height and deformation from interferometric SAR measurements. This is significant for the routine application of SAR interferometry in fields like digital elevation mapping and large scale deformation mapping.

Abstract: In a method for azimuth scaling of SAR data without interpolation, raw SAR data in azimuth are multiplied with a phase function H.sub.5 (f.sub.a ;r.sub.o), where f.sub.a denotes the azimuth frequency and r.sub.o denotes the range to a target point, and where a desired scaling factor is entered into the phase function. An azimuth modulation of the SAR data is subsequently adapted with the phase function H.sub.5 (f.sub.a,r.sub.o) to that of a reference range, in a manner so that the azimuth modulation no longer depends on the range. In a last step of the process, a quadratic phase modulation is performed in the azimuth so that, in order to attain an azimuth processing with a very high phase accuracy, the azimuth frequency modulation becomes exactly linear.

Abstract: A cell averaging (CA) constant false alarm rate (CFAR) device for use in a radar system which filters noise and clutter from a signal containing a plurality of range cells. A moving window average calculator (MWAC) calculates a moving window average (MWA) for each range cell in a signal. A central processing unit (CPU) estimates a skew factor of a probability density function (PDF) and calculates an offset factor based on information contained in the signal. A multiplying device multiplies the offset factor by the MWA calculated for each range cell and creates a second signal containing a plurality of range cells. A comparator compares each range cell of the second signal to each corresponding range cell of the original signal, selects a the larger value of the two signals, and creates a third signal which is essentially free of noise and clutter.

Abstract: A method and apparatus for preventing the occurrence of range ambiguities and Doppler ambiguities in both a radar and sonar environment. A series of N pulses are produced, each of which contains a number of contagious subpulses. Each of the subpulses exhibit a different frequency than the remaining subpulses in that particular pulse. Furthermore, the order of appearance of the subpulses in each of the pulses is unique with respect to the remaining pulses in the series. A matched filter receiver and Doppler processor are used to provide auto correlations and cross correlations to prevent the range ambiguities and Doppler ambiguities.

Abstract: A system 10 for reducing clutter in passive radiometric images of the ocean surface, the system including: a first polarizer 12 for generating a vertically polarized image of a selected patch of the ocean surface, the vertically polarized image including a first set of radiance data; a second polarizer 14 for generating a horizontally polarized image of the selected patch of the ocean surface, the horizontally polarized image including a second set of radiance data; a processor 16 for computing a clutter reduction weighting factor from the first and the second sets of radiance data; and means 18 for combining the first set of radiance data with the second set of radiance data utilizing the weighting factor to generate a combined image with reduced wave clutter. The processor 16 includes means for computing a weighting factor for minimizing clutter-associated variance in the weighted combination of the first and the second sets of radiance data.

Abstract: For less expensive estimation the impulse response x.sub.MOS of a high-resolution, band-limited radar channel in a radar station operating with an expanded transmitted pulse a(t), from a received signal e, over which a correlated or uncorrelated additive interference signal n can be superimposed, with the use of knowledge about the spread code c and the use of a channel estimator with which a so-called linear, optimum unbiased estimation of the radar channel impulse response x.sub.MOS is performed in a time range covering M range gates of interest, the linear, optimum estimation in the unbiased channel estimator is modified in such a way that the pulse response x.sub.MOS of the band-limited radar channel is determined according to the basic principle of a multiplication of the sampled received signal e and an inverse estimation matrix A.sub.E.sup.-1. The matrix A.sub.E is formed by the extension of the rectangular matrix represented by the components c.sub.

Abstract: The radar signal processing apparatus according to the present invention comprises a noise distribution measurement system comprising an edge detecting circuit, a noise distribution measuring circuit, a template, and a pattern matching circuit and an adaptive type target detecting circuit.

Abstract: A system (10) for reducing range sidelobes adapted for use with pulsed radar systems. The inventive system (10) includes a mismatched filter (90) for correlating a received signal (84) with a correlator signal (92) having a different length than the transmit signal (84) and for providing a predetermined number of reduced range sidelobes (97) at the output of the mismatched filter (90). The mismatched filter (90) has a first locally optimum sequence that is the correlator signal (92). The mismatched filter (90) has an input device (86) for receiving an extended locally optimum sequence (84) that is a received signal (84). The first locally optimum sequence (92) is a sub-sequence of the extended locally optimum sequence (84). In a specific embodiment the mismatched filter (90) has a Barker-based code that is the correlator signal (92). The mismatched filter (90) has an input device (86) for receiving an extended Barker-based code that is a received signal (84).

Abstract: Radar detection of accelerating airborne targets in accordance with the present invention utilizing a sequence of velocity, acceleration matched filters. This system includes a transmitter generating a signal oscillating at a predetermined frequency controlled by modulator such that the transmitter repeatedly outputs short duration pulses. The output pulse frequency is passed to an antenna that radiates the energy into free space. Reflected electromagnetic wave energy is received by the antenna to produce a radar return signal that is processed to a receiver that includes a radio frequency amplifier having an output that is mixed with a local oscillator signal an applied to an IF amplifier. An output of the IF amplifier is mixed with the output of an IF oscillator where the mixed signal passes through a low pass filter to a pulse compression network. An output of the pulse compression network is input to a matched filter processor array having multiple outputs applied to an adaptive threshold detector.

Abstract: In a method to resolve ambiguities in a phase measurement for application in radar interferometry, a frequency estimation method is used, starting from conjugate complex products of pairs of adjacent pixels in an interferogram. The resolution of these products is subsequently reduced through successive addition or averaging, after which the differential phase of adjacent resolution levels is determined in each resolution level. The sum of the phase differences yields the estimated value for the phase gradient which is then used in a known method, such as the least-squares method, to reconstruct the absolute phase, thus resolving the phase ambiguities. The method according to the invention serves to resolve phase ambiguities in radar interferograms without producing the known distortions produced by the existing methods. The method is also robust at low coherence values as they occur in repeat-pass interferometry where the existing methods fail.

Abstract: An apparatus and method for radar detection of spectral moments and other spectral characteristics of echoes includes an agile antenna which directs an antenna beam in a direction for a dwell interval. A clutter filter reduces clutter. In order to eliminate the need for fill pulses to stabilize the clutter filter, the clutter filtering is accomplished by matrix multiplication of the echo signal in each range bin by the inverse of the covariance matrix for that range. This reduces the dwell at each range interval, and provides a stream of pulse-to-pulse information at each range interval. The pulse-to-pulse data in each range interval is spectrum analyzed to extract the desired spectral information, which is displayed.

Abstract: A method and apparatus for enhancing resolution of range estimates in all echo location systems and, specifically, such systems as Radar, Sonar, and Synthetic Aperture Radar (SAR), for example. The invention utilizes high order signal processing to "sharpen" or contract the main lobe of the processing system ambiguity function and suppress its side lobes, for a given transmission pulse bandwidth. The method and apparatus may be implemented in the frequency domain or time domain. Enhanced resolution is achieved by using a filter (MSC filter), according to this invention, in the echo location data processing system so that the received echo data is processed by the MSC filter to produce a signal that exhibits enhanced range resolution. The MSC filter output, H(.omega.), which is specific to the transmitted pulse waveform, is the ratio of a high-order manipulation of the transmitted signal with its modified spectral profile.

Abstract: Hard-wired analog adaptive cancellation for microwave receivers to cancel the interference generated by co-located transmitter employs a circuit having two or more quadrature taps on a delay line. The least and greatest delays provided by the delay line taps are selected so that the copies of the transmitted signals provided by the respective taps bracket the timing of the portion of the transmitted signal that leaks into the collocated receiver's input. Samples of received signals corrupted by interference from the transmitter are mixed with delayed samples of a transmission reference signal to develop a cancellation signal.

Abstract: A radar tracking system 100 adapted for use with existing radar tracking systems. The inventive system includes a radar target detection system 106, 108 for detecting radar targets in clutter using magnitude and angular position information obtained from return signals. A tracking algorithm 104 is used to track and update the positions of said targets with respect to the position of the radar system. The tracking algorithm includes a true target angle estimator 110 for maintaining accurate target angle information when the target is clutter and when the target is out of clutter. The tracking algorithm maintains accurate target distance information when the target is in clutter and when the target is out of clutter. In a specific embodiment, accurate distance information is maintained in a track file 122 where the amplitudes of return signals are stored once a target is detected by the detection system 100.

Abstract: A signal processing system applies space-time adaptive processing ("STAP") to an airborne surveillance Doppler radar comprised of a single-channel, rotating antenna. The STAP substantially improves signal-to-interference-plus-noise ratio ("SINR"), thereby improving the detection of weak targets.

Abstract: The traditional minimum antenna area limit for synthetic aperture radar (SAR), imposed by ambiguity considerations, is eliminated by using a transmitter format providing distinguishable sub-pulses. Signal formats which are feasible for implementing such sub-pulses include frequency-division (i.e., a distinct frequency band is used for each sub-pulse), and code-division (i.e., sub-pulses occupying the same frequency band are grouped in distinguishable combinations). The nominal pulse period is divided into N sub-pulses, and the sub-pulse group is transmitted with the nominal pulse repetition frequency (f.sub.p). The range ambiguities are determined by the repetition rate of the sub-pulse group (f.sub.p) and the azimuth ambiguities are determined by the repetition rate of the sub-pulses (N.f.sub.p).

Abstract: A continuous wave ranging system comprises a modulator for modulating an r.f. carrier signal in accordance with a pseudo random code, a transmitting antenna for radiating the signal towards a target, a receiving antenna and receiver for detecting the signal reflected from the target, a correlator for correlating the detected signal with the transmitted code with a selected phase shift corresponding to the current range gate to be tested, whereby the range of the target from the system may be determined, and filtering means for filtering from the output of the correlator those range gate amplitudes which vary with a frequency less than a predetermined value.

Abstract: One meter and one foot resolution is achieved in a multi-mode SAR radar system in real time by wide bandwidth RF signal generation, precision motion compensation, polar reformatting, autofocusing and high dynamic range image processing. An exciter/receiver of this system includes means for providing wideband RF waveform generation and down-conversion, while a programmable digital signal processor includes improvements in software for implementing the functions of motion compensation including the presuming of data, polar reformatting, autofocusing and image processing.

Abstract: An ADPCA subsystem includes a weight processor for weighting the delta channel signal according to the results of an adaptive algorithm to which the output of a DPCA vector combiner is input. An AMTI vector combiner is connected to the output of the DPCA vector combiner to form the filter output. The delta channel signal is time delayed and samples of the delta channel signal are collected by the processor together with a sum channel sample and a residue sample, in order to apply the proper weights to the undelayed and delayed delta channel samples. The output of the ADPCA weight processor therefore provides an optimum correction signal to the vector combiner.

Abstract: A method and apparatus for detecting the presence of multipath interference within a radar receiver disposed to form sum (.SIGMA.) and difference (.DELTA.) signals by time-sampling a target return signal is disclosed herein. In accordance with this method there is formed a sequence of complex conjugates (.SIGMA.*) of the sum signals (.SIGMA.). Each of the .SIGMA.* signals is multiplied with an associated one of the .DELTA. signals so as to form a time-sampled sequence of .SIGMA.*.DELTA. signals. A power spectrum representation of the time-sampled sequence of signals .SIGMA.*.DELTA. is then generated, wherein the presence of selected spectral components within the .SIGMA.*.DELTA. power spectrum indicate the existence of multipath interference within the radar receiver. In a particular implementation the .SIGMA.*.DELTA. power spectrum representation is quickly and reliably determined by performing a Fast Fourier Transform (FFT) operation upon the time-sampled sequence of .SIGMA.*.DELTA. signals.

Abstract: The present invention is a block adaptive quantizer and an associated VLSI processor to provide real-time data compression for high resolution imaging radar systems. The block adaptive quantizer receives data from a synthetic radar aperture in a burst-mode. The block adaptive quantizer encodes and quantizes the data via a data-compression scheme. The image data is encoded by the block adaptive quantizer using thresholds generated from current bursts of image data collected.

Abstract: A computer-implemented process is disclosed for processing incoming target data from a focal plane or scanning radar to accomplish multiple Target Tracking. Inputs are pixel plane coordinates and intensity of target blips. The Intelligent Target Tracking Processor (ITTP) employs an optimal target tracking algorithm. An optimal observation-to-track assignment exists when all target blips in a new frame of target data are matched up with nearby tracks, such that the sum of all the distances from each target blip to its assigned track is minimized. An expert system is used to control overall processing flow and provide efficient allocation of computing resources. Target blips without near neighbors are allowed to go directly to a real track table of established tracks, if their coordinates match-up with projected tracking gates. Otherwise, target blips are tested sequentially against two-frame, three-frame, and four- or higher-frame discriminants, to reject blips not belonging to established tracks.

Abstract: A signal processor is described for object detection systems such as radar and sonar systems in which wave energy is transmitted and received as a train of discrete pulses of frequencies stepped in predetermined sequence. The received signal processor comprises a plurality of processing channels of number corresponding to the number of sub-pulses in the transmitted pulse train, each channel including frequency selective means such that signal returns of frequencies corresponding to but one of the transmitted sub-pulses are processed by that channel. Means are provided for simultaneously sampling the signal levels in all channels and indicating that channel in which the signal level is greatest, this sampling process being serially repeated at times related to each of the times of transmission of one sub-pulse of the train.

Abstract: This invention improves the detection performance of doppler radar by censoring clutter at the output of the doppler processor, and it functions in operative association with a range CFAR. By a selective rejection of signals based on doppler characteristics and on signal amplitude, it will reduce the sum of clutter and noise at the input to the CFAR. Thus the CFAR detection threshold level is lowered, which thereby improves the detection performance for moving targets.

Abstract: A modulation is applied to a received radar signal prior to analog-to-digital (A/D) conversion, and is removed subsequent to A/D conversion, to mitigate the effects of nonlinear receiver harmonic distortions and receiver spurious responses. The received target and clutter signals pass unchanged through the receiver to the digital signal processing. Harmonic distortion products and spurious responses introduced in the receiver after the modulation has been applied are distorted by the demodulation signal. By proper selection of the modulation waveform, coherent harmonic distortion products and spurious responses are converted to wideband noise reducing the level of interference that competes with targets in the affected Doppler filters.

Abstract: The invention relates to a radar apparatus (1, 2, 3) provided with a doppler filterbank (4) and fast thresholds (5.i), for writing per pulse a range-doppler matrix in range-doppler memory (6) and the background level in background memory (7). By unfolding the range-doppler matrices and combining the unfolded range-doppler matrices for all the pulses in a burst in combination means (10), an incoherent combination of the pulses is obtained before an actual detection takes place. This cluster before detect scheme increases the detection probability for weak echoes, without increasing the false alarm rate.

Abstract: An adaptive processor which uses the successive range and Doppler outputs of a conventional matched-filter to improve the signal-to-noise ratio for non white noise/clutter. The adaptive processor minimizes the output for a given range and Doppler cell with the constraint that the response to signals returning with specified range and Doppler offsets, with respect to the center of the range-Doppler cell, each have specified values. Weights are derived which can be applied to range-Doppler outputs in the neighborhood of the range-Doppler cell to minimize its output subject to the constraints. The weights depend on an estimate of the cross-covariance matrix of the various outputs of the range-Doppler cells that are to be weighted. The constraint parameters are specified in terms of the ambiguity function of the transmitted waveform.