Abstract: Method and device for determining an azimuth angle and/or an elevation angle, based on a multibeam radar system, in which the echo signals of each radar target are recorded over at least two beams. The amplitude of an echo signal recorded in each receiving beam is normalized. For each receiving beam, the normalized amplitude is compared to the pattern values of an antenna pattern stored and normalized for this beam in order to determine the angle of a radar target. The comparison results from at least two receiving beams are combined to form an angle-dependent analysis quantity, and the angle whose angle-dependent analysis quantity meets a minimum and maximum criterion is determined to be the angle of the radar target. Included in the angle-dependent analysis quantity is a phase angle of at least two recorded echo signals. This operation can also be performed on the basis of a complex normalization operation.

Abstract: In an FM-CW radar, a receive section has an array antenna in which a plurality of element antennas are arrayed as receive antennas, and a plurality of mixers for generating a beat signal of each channel from a receive signal for each element antenna, and a signal processing section comprises a first device for performing analog-to-digital conversion of the beat signal of each channel into a digital beat signal of each channel and storing it, a second device for performing a Fourier transform process for the digital beat signal of each channel to obtain Fourier transform data of each channel, a third device for performing a phase shift process according to beam direction angles for the Fourier transform data of each channel and thereafter synthesizing the Fourier transform data of each channel every beam direction angle to obtain Fourier transform data of each beam direction angle, and a fourth device for detecting a range to an object and a relative velocity of the object from the Fourier transform data of ea

Abstract: The process is used for suppressing the effect of signals that are received or sent via side lobes of an antenna (PA; HA) of an amplitude or phase monopulse radar device, in which for the purpose of position measurement of a first and, if need be, a second target (T1, T2) detected by the radar beam, three illumination functions Je(Lx), Jk(Lx) and Js(Lx) for the antenna (PA; HA) are provided for each measurement axis, as well as antenna functions Fe(X), Fk(X), and Fs(X) resulting from them. The first, second, and third illumination functions Je(Lx); Jk(Lx), and Js(Lx) are selected in this connection so that a quotient function Qe(X)=Fe(X)/Fs(X) or Qk(X)=Fk(X)/Fs(X), which is linearly or quadratically dependent on the target direction, is produced by normalizing the first and the second antenna functions Fe(X); Fk(X) with the third antenna function Fs(X). The power of this quotient is compared with at least one threshold value th.sub.e or th.sub.

Abstract: A system and a method for distance measurement utilizes a radio system. The distance is measured by determining the time it takes a pulse train to travel from a first radio transceiver to a second radio transceiver and then from the second radio transceiver back to the first radio transceiver. The actual measurement is a two step process. In the first step, the distance is measured in coarse resolution, and in the second step, the distance is measured in fine resolution. A first pulse train is transmitted using a transmit time base from the first radio transceiver. The first pulse train is received at a second radio transceiver. The second radio transceiver synchronizes its time base with the first pulse train before transmitting a second pulse train back to the first radio transceiver, which then synchronizes a receive time base with the second pulse train. The time delay between the transmit time base and the receive time base can then be determined.

Abstract: This invention consists of a method for measuring the direction and magnitude of the semi-major and semi-minor axes (13, 14) of the electric ellipse (5) of an incoming wave in a magnetized plasma from the in-phase and quadrature measurements (12) of the electric field that is measured on three orthogonal antennas (1, 2, 3), in order to measure the line-of-sight of the direction of wave propagation (15), and the wave propagation mode (16, 17), from the orientation and rotation sense of the measured wave electric ellipse. In addition, for a wave that consists of a linear combination of the ordinary and extraordinary modes in a magnetized plasma, these measurements can also be used to measure the line-of-sight of the direction of wave propagation (20), and the Faraday rotation angle (21), from the orientation of the semi-major axes of the electric ellipse (17, 18) that are measured at two or more adjacent frequencies.

Abstract: A microwave sensor for determining the velocity and direction of a moving object comprises a mixer, phase shifter, and receive/transmit antenna mounted in series, the mixer having a single intermediate frequency output. The intermediate frequency output is switched synchronously with the phase shifter which is switched between 0.degree. phase shift and 45.degree. phase shift. Although the mixer has only a single intermediate frequency output, the switching provides two output channel signals and with a phase difference of 90.degree. therebetween to enable determination of the direction of movement. The single intermediate frequency channel provides intrinsic gain matching of the output channels which eliminates the need for tuning in order to balance output channels as required in conventional sensor.

Abstract: A down range returns simulator for generating simulated radar reflected returns for testing advanced radar waveforms and associated signal processing. The simulator generates return signals based from real mission data, data transforms, arbitrary reference waveform convolutions, and radio and intermediate frequencies. The simulator includes a source of field data, synthetic target, an analog to digital converter for generating digital waveform returns, and RF/IF waveform generator, and a source of clutter waveform characteristics (OPINE, weather, and electronic counter-measures effects). The RF/IF waveform generator uses FFTs and IFFTs in order to develop realistic digital samples for evaluation software and Doppler images. The simulator apparatus provides a target return simulation as if received by radar in a down range mission flight test without the costly expense of conducting a mission flight test for collecting the appropriate data signatures for evaluation.

Abstract: A Deramp type radar used in synthetic aperture radar for radar imaging transmits coherently repeated linear frequency-modulated pulses and carries out a sort of pulse compression in reception by demodulation of the echo signals received by means of a frequency ramp that reproduces all or part of a transmitted pulse, and by a Fourier transform performed in range. The application to a Deramp type radar signal of a standard SAR processing is disturbed by the fact that, in this signal, the effectively demodulated part of an echo signal due to a target has a position with respect to this echo signal and a duration that are variable as a function of the distance from the target to the radar. The proposed method makes it possible to eliminate this disturbance by means of a particular choice of a common temporal support used for the demodulation of the signals of all the targets of the useful swath and a phase correction applied to the level of the pulse response of the image focusing filter of the SAR processing.

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: Automatic focusing of radar or sonar imaging systems, for example, synthetic aperture radar (SAR) or synthetic aperture sonar (SAS) systems, is accomplished by using high order measurements, such as the quadruple product of the range compressed signal g(x). The phase error is estimated by a recursive or non-recursive algorithm from the phase of the quadruple product. The estimated phase error is applied to the range-compressed SAR or SAS image data which is then azimuth compressed to obtain the focused image data.

Abstract: A processing method for use in providing improved SAR imagery at high duty factors that provides for enhanced radar sensitivity. Radar signals are transmitted that embody a high duty factor ultra-high resolution SAR waveform generated using a biphase code with a predetermined high pulse compression ratio. Received radar returns comprising a SAR map are Fourier transformed and multiplied by a stored set of complex weights. The resultant Fourier transformed complex weighted SAR map is then inverse Fourier transformed to obtain compressed range bins. The inverse Fourier transformed SAR map is then processed for display.

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: A leakage calibration and removal system and method estimates the complex in-phase and quadrature phase (I/Q) components of a leakage signal for each beam location in the sampled down-converted radar signal in a radar system (10). In a digital embodiment, the stored leakage calibration signal (264) is subtracted (206) from the sampled radar signal, and the resultant signal is processed (208, 210, 212) to detect targets. A leakage calibration process (250) is activated if a leakage signal test (214) indicates a problem for a sufficient number of consecutive scans (216), wherein for each beam location, M consecutive I/Q waveforms are averaged (252), known targets are removed (254, 256, 258), and the resulting signal is scaled (262) and stored (264) as a new leakage calibration signal if the variance is within acceptable limits (262).

Abstract: Methods that compensate for phase errors caused by path length variations in a radar system, and that compensate for relative phase errors in upconvertor and downconverter references employed in the radar system. One method samples a signal reflected from a duplexer through a receiver during the time the radar pulse is transmitted. The signal reflected from the duplexer is compared to a radar echo pulse on a single pulse basis. The phase of the sampled signal is subtracted from the phase of the received radar echo pulse reflected to determine the phase error. In a second method, multiple samples are collected during the time each radar pulse is transmitted. Samples of the signal reflected from the duplexer and the radar echo pulse are compared on a pulse to pulse basis. The phase differences are averaged across the pulse duration. The averaged phase differences are integrated on a pulse to pulse basis to determine the phase error.

Abstract: An automotive radar incorporates a repetitive randomized equivalent LFM sequence of frequencies for improved immunity to jamming from other automotive radars. Each frequency in the sequence is of sufficient duration to travel round trip over the detection range of the radar. The Doppler shift in the received signal is estimated by performing a spectral analysis on similar frequency components of the received signal, and is then removed from the entire received signal. The received signal is then reordered so as to form an equivalent LFM received signal, and is compared with a similarly reordered image of the transmitted signal so as to estimate the range to the target. The randomization sequence, initial start frequency, or initial start time of the repetitive sequence are varied to minimize the effects of jamming by other radars, and this variation can be directionally dependent.

Abstract: A method of correcting an object-dependent spectral shift in radar interferograms has two main procedures. In the first, the phase of the interferogram is reconstructed through phase unwrapping and subsequently smoothed for reducing noise. In the second, the two complex-value radar images intended for forming the interferogram are suitably multiplied by a factor derived from the smoothed phase, and are subsequently low-pass-filtered. The spectral shift dependent on the local inclination of the terrain is thus adaptively corrected and the decorrelation caused by the image geometry is extensively eliminated. Particularly in the region of critical, mountainous terrain, the phase noise drops to a very low level.

Abstract: A Deramp type radar used in synthetic aperture radar for radar imaging transmits coherently repeated linear frequency-modulated pulses and carries out a sort of pulse compression in reception by demodulation of the echo signals received by means of a frequency ramp that reproduces all or part of a transmitted pulse, and by a Fourier transform performed in range. With this type of pulse compression, a parasitic phase modulation appears on the signal delivered by a Deramp type radar. This parasitic phase modulation disturbs the standard SAR procession operations for the construction of radar images. The proposed method is used to eliminate the detrimental effects of this parasitic phase modulation on the construction of a radar image.

Abstract: I/Q imbalance correction is performed directly in the frequency domain by exploiting the symmetry properties of the discrete Fourier transform (DFT) of a real signal, taking the in-phase component as the real part and the quadrature component as the imaginary part. Amplitudes of ordered real and imaginary spectral components are respectively summed with reverse-ordered real and imaginary spectral components, the sums complex multiplied with correction values derived through calibration and selected in accordance with a maximum magnitude spectral component and the results of the complex multiplication summed with the real and imaginary spectral components. Simplified processing architecture and improved performance for a given level of processing power is thus provided.

Abstract: An apparatus for measuring the height and cross-track offset of a surface location from a moving platform is defined. First and second antennas positioned on an underside of the platform are directed downwardly toward the surface. A transmitter associated with one of the antennas transmits a signal toward the surface. A first coherent detector associated with the first antenna detects a received signal corresponding to the transmitted signal as reflected by the surface and generates in-phase and quadrature components of the detected signal relative to the transmitted signal. A second coherent detector associated with the second antenna detects a received signal corresponding to the transmitted signal as reflected by the surface and generates a second set of in-phase and quadrature components of the detected signal relative to the transmitted signal. An analog to digital (A/D) converter converts the in-phase and quadrature components into digital information stored in a memory.

Abstract: Apparatus (10) for generating a radar waveform (W). A noise generator (20) generates a series of pulses in a pseudo-random pattern, and a frequency generator (16) generates a carrier wave having a frequency within a predetermined band of frequencies. The carrier wave is modulated with the pseudo-random pattern of pulses, and the resulting modulated carrier wave passed through both a filter (30) and an attenuator (32) to suppress any discernible feature or signal characteristics of the resulting waveform. The modulated carrier is transmitted by an antenna (42) and a received return signal is processed by a signal processor (100) to obtain pertinent information about a target. The transmitted waveform has no discernible attributes by which the waveform, if processed and analyzed by someone else's radar detector (E) would convey any intelligence as to the presence or source of the transmitted waveform.

Abstract: A phase detector includes a mixer circuit responsive to an input signal and a reference signal to produce an error signal which is a function of the phase difference between the input signal and the reference signal; a phase shifting circuit varies the phase difference between the input and reference signals; a control circuit responsive to the error signal provides a drive signal to the phase shifting circuit to set to quadrature the phase difference between the input and reference signals; and a phase indicator device responsive to the drive signal indicates the phase difference between the component and reference signals.

Abstract: A method and apparatus for improving resolution of targets in a monopulse radar beam.

Abstract: In the case of this radar sensor, a phase shifter is inserted between a microwave generator and an antenna and can be switched over between two phases. A demodulator (DM) demodulates the received reflected signal, which has superimposed on it the microwave signal which originates from the microwave generator. A de-multiplexer (DEMUX) which is connected downstream of the demodulator (DM) separates the two phase-shifted demodulated signals. The measurement result is largely noise-free.

Abstract: A synthetic aperture radar apparatus which analyzes Doppler frequency displacements arising from a range direction motion component of a target and motion components of a flying body to produce a motion target image wherein only azimuth direction motion components of the target are converted into Doppler components. An SAR apparatus wherein SAR reproduction processing is performed based on target information obtained from a reflected wave received from a target and flying information of a flying body includes a recording and reproduction unit for recording the target information and reproducing the data in a designated range, and a moving target processor for analyzing Doppler frequency displacements arising from a range direction motion component of the target and motion components of the flying body from the reproduced data and producing a moving target image wherein only azimuth direction motion components of the target are converted into Doppler components.

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 process and the corresponding phase or amplitude-single pulse radar device are used to locate a first and possibly a second target (TT1, TT2) detected by the radar beam from the direction x1, y1; x2, y2. The extended single-pulse aerial of the radar device has at least three partial aerials for a first measuring axis x (e.g. azimuth) which are arranged in such a way, have such directional characteristics and the signals of which are combined together and weighted in such a way that two mutually linearly independent, purely real or purely imaginary aerial functions which are independent of target displacements perpendicular to the first measuring axis are formed. The function course of these aerial functions F1(x) and F2(x) is measured for the individual case and the functional values dependent upon the target displacement x are stored in the storage unit (MEM). Measurements are found for the targets of the position x1 and x2 detected by the radar beam according to the aerial functions F1 and F2.

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: 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: This invention relates to a method and apparatus by which a coarse estimate of radar signal polarisation can be obtained. An array comprises at least three differently directed detectors. The polarisation is estimated by measuring an amplitude relationship, such as a ratio of amplitudes, for two adjacent detectors and for two non-adjacent detectors. This provides sufficient information to obtain a coarse estimate of the polarisation state, obtainable by using the value of the amplitude relationship for the two adjacent detectors together with a look-up table to estimate values of the amplitude relationship for the two non-adjacent detectors for different polarisation states, and then comparing the measured and estimated values for this amplitude relationship.

Abstract: A radar system in which a frequency agile synthesizer is used to provide rapid frequency shifts and in which measures are taken to maintain phase coherency. The system is fully coherent such that all signals are derived from a common source and are capable of high pulse repetition rates in excess of 1 MHz. There are no inherent transmit duty cycle restrictions and the system is able to transmit complex phase and frequency modulated waveforms. A frequency interleaving scheme is used to resolve range ambiguities at high pulse repetition frequencies and the use of a complementary phase coding scheme allows a high range resolution processing with the transmitted waveforms.

Abstract: A method of computing and correcting phase errors due to atmospheric turbulence in a dual-antenna multiple-pass synthetic array radar (SAR) interferometer system. The method improves topographic mapping accuracy at very long ranges. The method computes an atmospheric correction from the residual phase difference between a two-pass interferometer output (containing atmospheric phase errors) and a dual-antenna single-pass interferometer output (for which atmospheric phase errors cancel because the two channels are collected simultaneously). The residual phase measured in a single resolution element is then filtered by averaging over an area of many resolution elements, typically on the order of several thousand resolution elements. This exploits the long correlation distance of the atmospheric phase errors to reconstruct the dominant low-frequency part of the error spectrum. In addition, unwrapping the phase of the output of the complex Wiener filter produces an atmospheric turbulence measurement map.

Abstract: Apparatus (10) for generating a radar waveform (W). A noise generator (20) generates a series of pulses in a pseudo-random pattern, and a frequency generator (16) generates a carrier wave having a frequency within a predetermined band of frequencies. The carrier wave is modulated with the pseudo-random pattern of pulses, and the resulting modulated carrier wave passed through both a filter (30) and an attenuator (32) to suppress any discernible feature or signal characteristics of the resulting waveform. The modulated carrier is transmitted by an antenna (42) and a received return signal is processed by a signal processor (100) to obtain pertinent information about a target. The transmitted waveform has no discernible attributes by which the waveform, if processed and analyzed by someone else's radar detector (E) would convey any intelligence as to the presence or source of the transmitted waveform.

Abstract: A passive imaging system that uses an antenna having two antenna elements. The system cross-correlates received signals with a reference function to achieve high resolution. The antenna elements are rectangular with their long dimensions oriented normal to the longitudinal axis of a carrying vehicle and the elements are separated by a distance consistent with image resolution requirements. Additionally, the antenna elements are frequency scanned in the cross-track dimension. The channel for the forward antenna element has a time delay relative to that of the rear antenna element. This time delay achieves pointing of the antenna at a particular forward angle relative to the normal to the velocity vector. Outputs of IF filters of the antenna elements are synchronously detected to provide in-phase and quadrature (I/Q) components of their phase modulated product.

Abstract: A radar digital IF (intermediate-frequency) signal is to be complex demodulated, then processed through a two-channel real lowpass filter, prior to Doppler correction, clutter filtering, and other usual processing steps. A particularly efficient form of lowpass filtering for such applications is the so-called CIC (cascaded integrator/comb) filter. The first stage of such a filter is always an integrator. A conventional mechanization would therefore feature a conventional complex demodulator followed by an accumulator on each of the two demodulator outputs, followed by more processing. This invention more efficiently mechanizes this function by replacing the usual pair of multipliers and pair of accumulators (or integrators) with a single two-delay (54, 58) accumulator having an add/subtract control (48) on the input adder (42), and a pair of multiplexer switches (62, 66).

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: An apparatus and method of homodyne reception includes power divider circuitry for providing first and second signals from an input signal. Oscillator circuitry generates first and second oscillator signals. The first signal and second oscillator signal are mixed and the second signal and the second oscillator signal are mixed in first and second modulator circuitry, respectively, to provide first and second mixed signals which are further mixed together in image reject mixer circuitry. Amplifiers are used to amplify one of the signals before it is mixed with an oscillator signal and to amplify one of the mixed signals before it is mixed with the other mixed signal in the image reject mixer circuitry. In each of the mixing steps of the preferred embodiment is a filter which filters out spurs in the signals.

Abstract: A pseudorandom noise coded system (100) compensates for imperfections, improving out of range rejection, and includes a digital correlator (200) having a first complex multiplier (202) receiving a sequence of sampled data words and a sequence of precomputed complex data words and producing a sequence of first complex product words. A second complex multiplier (204) receives the sequence of first complex product words and a precomputed constant word and produces a sequence of second complex product words. A complex multiplexer (206) receives a sequence of binary code states, and the sequences of first and second complex product words and produces a sequence of complex multiplexer output words formed as a replica of either the first or the second complex product words, depending on the binary code. A complex accumulator (208) receives the sequence of complex multiplexer output words and produces a complex accumulated sum word formed as a complex sum of the complex multiplexer output words.

Abstract: This invention relates to a method and apparatus for controlling a biphase modulator (602, 702) to improve autocorrelation in pseudorandom noise coded systems. The biphase modulator modulates a carrier frequency with one of two phase states responsive to a pseudorandom noise (PN) binary code sequence. The spectrum (610, 710) at the output of the biphase modulator comprises a plurality of spectral lines separated by the code repetition frequency, including a center spectral line (611, 711) and at least one adjacent spectral line (612-615, 712-717). The magnitude of the center spectral line is measured and compared to a reference to produce a control signal which is responsive to the magnitude of the center spectral line. This control signal is supplied to the biphase modulator for maintaining a predetermined magnitude of the center spectral line thereby achieving a desired spectrum output and improving autocorrelation of the system.

Abstract: An apparatus and method are described for direction finding the source of emf emissions including a monotone signal by detecting the phase changes of the monotone signal during movement relative to the source. A software embodiment measures the amount of phase change.

Abstract: A secondary radar uses monopulse reception techniques to improve the estimate of the aircraft position and to improve the reliability of the reply decoding process. Digital signal processing techniques are utilized to replace the analog circuit used in the prior implementations. The secondary radar implements monopulse processing using a half angle phase method wherein the sum and difference signals are encoded in a complete phasor. The detection of the signal and extraction of the azimuth angle data is implemented using a digital receiver concept. The complex phasor is sampled at an intermediate frequency, down converted to baseband and detected. The azimuth angle is computed using arithmetic methods implemented by digital signal processing circuitry.

Abstract: A multipath signal preprocessor which permits coherent bistatic radar detection with a single omnidirectional antenna is provided. The multipath signal preprocessor separates multipath signals received at an antenna into a strong path signal and a weak path signal. The received multipath signal after filtering, amplifying, and heterodyning is separated into in-phase and quadrature signal components. A constant magnitude signal estimate having approximately the frequency and phase of the strong path signal from the multipath signal is generated. An estimate of the amplitude of the strong path signal is generated from the received multipath signal amplitude. The estimate of the amplitude of the strong path signal is multiplied by the constant magnitude signal estimate having approximately the frequency and phase of the strong path signal to obtain an estimate of the strong path signal.

Abstract: A modular radar system using both FM/CW and pulse waveforms for automotive collision avoidance applications.

Abstract: A frequency range gate closure circuit for use in synthetic aperture radars that incorporate a digital waveform generator or direct digital synthesizer that improves the mapping resolution of the radars. Range gate closure motion compensation is more accurately implemented using the present circuit. The digital waveform generator or direct digital synthesizer is clocked by a system clock, and processes control words corresponding to a desired slope of the stretch frequency modulation of transmitted radar signals, to generate frequency modulated pulse output signals. The range gate closure circuit includes a digital data accumulator for receiving an increment value and a pulse repetition frequency value of the radar. Logic circuitry is coupled to an output of the digital data accumulator and is coupled to receive a digital modulo threshold signal and output the increment value when it is less than the digital modulo threshold signal every pulse repetition interval.

Abstract: A wide band ground penetrating radar system (10) embodying a method wherein a series of radio frequency signals (60) is produced by a single radio frequency source (16) and provided to a transmit antenna (26) for transmission to a target (54) and reflection therefrom to a receive antenna (28). A phase modulator (18) modulates those portion of the radio frequency signals (62) to be transmitted and the reflected modulated signal (62) is combined in a mixer (34) with the original radio frequency signal (60) to produce a resultant signal (53) which is demodulated to produce a series of direct current voltage signals (66) the envelope of which forms a cosine wave shaped plot (68) which is processed by a Fast Fourier Transform unit 44 into frequency domain data (70) wherein the position of a preponderant frequency is indicative of distance to the target (54) and magnitude is indicative of the signature of the target (54).

Abstract: Apparatus including a multi-scale adaptive filter for smoothing interferometric SAR (IFSAR) data in areas of low signal-to-noise ratio (SNR) and/or coherence while preserving resolution in areas of high SNR/coherence. The multi-scale adaptive filter uses simple combinations of multiple linear filters applied to a complex interferogram. The multi-scale adaptive filter is computationally efficient and lends itself to parallel implementation. A pyramid architecture comprising a plurality of cascaded stages is employed which reduces the computational load and memory required for implementation of the processing algorithm. The multi-scale adaptive filter implements a processing algorithm that may be applied to standard IFSAR data. Its input is a complex interferogram (the conjugate product of two complex images) and its output is a filtered interferogram (A) which is passed to an information extraction processor, that extracts a terrain elevation map, for example.

Abstract: An apparatus is disclosed for detecting the shape of an object by means of radar. A transmitter 1 forms signal units wherein the transmitting frequency is varied continuously and linearly within a predetermined frequency bandwidth. By repeating this signal unit at fixed periods, a transmitting signal having a continuous waveform is generated. A receiver 5 detects signals reflected from a target 11, and converts them to video signals. An A/D converter 6 samples these video signals and digitizes them. The digitized video signals are stored in a first two-dimensional memory 7 according to a transmitting frequency index and a transmitting period index. A range compression device 8 resolves sequences of these digital video signals in a range direction by performing an inverse Fourier transformation on columns of data stored in the memory 7 which have the same transmission period.

Abstract: Synthetic aperture radar imaging for nonlinear trajectories utilizing range relative doppler processing, invariant mapping of information from arbitrary shaped cells onto an X--Y coordinate system, and round trip signal delay which allows accurate synthesis of a reference signal for each range cell. A synthetic signal synthesizer produces the reference signal for synchronous demodulation in the radar.

Abstract: The present invention is an interferometric SAR system and processing method that combines multi-pass SAR interferometry with dual-antenna SAR interferometry to obtain elevation maps with accuracy unobtainable by either method alone. A single pass of the dual-antenna system provides coarse elevation maps. High accuracy maps are obtained through additional passes, with accuracy determined by the number of passes. The processing method combines the acquired data to provide a calibrated, high precision, low ambiguity elevation map, using approximate least-squares and maximum-likelihood processing methods. The present dual-antenna SAR interferometer collects two complex SAR images from slightly different elevation angles on a single pass using two antennas on the same platform. The present invention provides calibrated maps that have coarse precision but are nearly unambiguous because of the small interferometer baseline.

Abstract: A radar signal processor for use in a pulse radar system. Reception signals are given from a range divide and output circuit to a plurality of integration point variable coherent integrators, each of which is allocated to a different range domain. The range domain is given to an integration point setting section provided corresponding to each integration point variable coherent integrator. The integration point setting section determines the number of coherent integration points based on the given range domain and sets it in the corresponding integration point variable coherent integrator. The signal resulting from coherent integration by the integration point variable coherent integrator is discriminated to frequencies, then supplied to any square detector for square detection for each frequency component. Square detection output is fed into a CFAR detector, which then makes its false alarm rate constant for a supply to a display, etc.