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: An improved range migration algorithm or processing method that advantageously performs digital synthetic aperture radar image formation processing. The range migration algorithm provides high-resolution, large-area spotlight SAR imaging that is free from phase and gain discontinuities and geometric distortions. The range migration algorithm also provides for truly scalable and portable processing. The range migration algorithm may be used in a real-time implementation on a multi-processor platform. The range migration algorithm of the present invention does not perform range deskew, which results in more efficient processing and the imaging of very large swath widths. In addition, the range migration algorithm explicitly and efficiently treats the residual video phase term. Also, no overcollection of input data is required.

Abstract: Method and apparatus for developing high range resolution radar target profiles. An outgoing radar waveform is encoded with coefficients corresponding to a wavelet transformation and then transmitted in the direction of a radar target. Incoming waveforms, including return waveforms reflected from the radar target, are decoded using an inverse wavelet transform to produce a high range resolution profile of the target. In an exemplary embodiment, the outgoing waveform is phase-shifted to create finite-duration waveform pulses, each pulse having a phase-state pattern corresponding to a set of coefficients in a transposed wavelet transform matrix. Phase-state duration is adjusted to achieve a desired range resolution.

Abstract: Disclosed are global navigation satellite system (GNSS) receivers, including digital spatial nulling arrays, and a method of providing antenna pattern outputs using the same. The digital spatial nulling array receives multiple antenna element inputs. A fast Fourier transform (FFT) is applied to the multiple antenna element inputs to obtain frequency domain representations of the multiple antenna element inputs. The antenna pattern outputs are provided by the spatial nulling array as a function of the frequency domain representations of the multiple antenna element inputs.

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: Coherent bursts of N wideband, low repetition frequency width-modulated pulses are transmitted, and they are received with pulse compression and then sampling. For each range gate and each speed hypothesis, a selection is made of the corresponding samples of N repetitions of a burst after compensation for the migration in distance. On each set of N samples, for a given speed hypothesis, a Fourier transform and a threshold-setting operation are performed. The distance and the unambiguous speed of the detected targets are then extracted.

Abstract: A broadband gigahertz frequency range radio receiver useful in electronic warfare and other applications for incoming signal detection and identification purposes. The receiver is based on Fourier transform examination of incoming signal characteristics and provides real time accomplishment of these tasks by way of using a simplified one-bit digital representation of the incoming signals and a resulting reduction of the computational load associated with the Fourier transform operation. The receiver precedes the Fourier transform operation with signal processing which may include, for example, a limiting amplifier and two bandpass filters. Two incoming signal accommodation is provided, a characteristic which is particularly improved over the characteristics of popular presently used receivers in this field.

Abstract: Special mathematical techniques are used to process accurate energy measurements in the focal plane of a high quality imaging system to produce high resolution images. The improved resolution exceeds the generally accepted Rayleigh limits. That is accomplished by adapting Fourier transform techniques and using both in-phase and quadrature or amplitude and phase components to recover the target scene. The measurement of the in-phase and quadrature or amplitude and phase components are taken in the focal plane and undergo parallel processing to preserve both amplitude and phase in the resulting image. A Fourier transform of the aperture characteristics is removed from a Fourier transform of the energy components to result in a Fourier transform of the image. The scene is recovered by taking an inverse Fourier transform of the result.

Abstract: The wireless communication system transmits signals using radios (205). The radios (205) receive a signal which is formatted for transmission (602). The formatted signals from the radios (205) are divided. One formatted signal is input directly to a transform matrix (207) and a copy of the formatted signal is input to a delay (206) before being input to the transform matrix (207). Transform matrix (207) transforms (604) the input signals into output signals that each contain a portion of the input signals. The outputs from the transform matrix (207) are then amplified (605) using the amplifiers (208). The outputs from the amplifiers (208) are inverse transformed (606) in an inverse transform matrix (209). The inverse transform matrix (209) serves to recombine the portions of the signals originally input to the transform matrix (207). The resulting signals are then transmitted using antennas (210).

Abstract: A multi-input amplitude and phase measuring method is disclosed for measuring the amplitudes and the phases of measurement signals at a high speed and with a high degree of reliability. Measurement signals received by antennae are converted into IF signals with local signals of frequencies f.sub.LO +.DELTA.f, f.sub.LO +2.DELTA.f, f.sub.LO +3.DELTA.f, f.sub.LO +4.DELTA.f by a mixer and then added by an adder, whereafter they are multiplied by an analog multiplier to convert phase information of the measurement signals into signals of frequencies .DELTA.f, 2.DELTA.f, 3.DELTA.f, 4.DELTA.f. Then, the signals obtained by the conversion are A/D converted and Fourier transformed to determine a spectrum. Then, in order to eliminate an influence of phase displacement by band-pass filters, the local signals are added by an adder and multiplied by a local signal of frequency f.sub.LO by a mixer, and the resultant signal is A/D converted and Fourier transformed to determine a spectrum.

Abstract: The Beamformer with Adaptive Processors is a practical joint spatial-templ processor suitable for combining multiple antenna signals for a communications receiver. The invention identifies a beam or beams, amongst a discreet set of fixed beams, for which adaptive locally optimum processing will most likely reveal the presence of a weak signal. The invention chooses a suitable form of adaptive locally optimum processing according to the nature of the beam or beams identified. The beam or beams are selected for adaptive locally optimum processing depending on several simple characteristics of a Fast Fourier Transform (FFT) of each beam's output. These are .SIGMA..sigma..sup.2, D, and B (the sum of the squares of the Fourier coefficients, the number of distinct peaks amongst these coefficients, and the total number of coefficients defining the peaks, respectively).

Abstract: An altimetric type measurement method for use on a satellite transmits a pulse towards the surface of the sea and carries out frequency transformation on the return signal resulting from the reflection of this pulse at the surface of the sea. This produces a spectral signal of samples successively comprising:(a)--a first zone with a low amplitude level,(b)--a second zone with a sharply increasing slope ending at a peak, and(c)--a third zone of decreasing slope.Samples of the spectral signal are selected within a selection zone that corresponds to the first and second zones for a predetermined maximal level of the height of the waves at the surface of the sea and maximum likelihood processing is applied only to the selected samples.

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: An FM radar apparatus detects a distance to and/or a speed of a target not only from peak frequencies of beat signals in respective frequency rise and fall regions but also by reusing the peak frequency in the preceding frequency rise or fall region. As a result, it becomes possible to obtain target data at twice the conventional pitch and hence to detect the target more finely and minutely.

Abstract: The present invention provides an apparatus and method for correcting buoy motion in Doppler moment estimates. In the present invention, it is assumed that the buoy is stationary over short periods of time, 0.5 seconds for example. The average pitch and roll angles are measured for the 0.5 second period. A short-term Doppler spectrum for a particular beam is computed and stored along with the corresponding average pointing angle. This short-term Doppler spectrum must be averaged with many others to be able to detect the clear air signal. To correct for motion broadening, the present invention shifts each short Doppler spectrum some number of velocity bins before averaging them together. This shifting scales the measured radial velocity at some measured pointing angle to the radial velocity that would have been measured if the antenna was pointing at some initial pointing angle, typically the steering angle if the antenna was level.

Abstract: An apparatus and method for detecting an object and determining the range of the object is disclosed. A transmitter, coupled to an antenna, transmits a frequency-modulated probe signal at each of a number of center frequency intervals or steps. A receiver, coupled to the antenna when operating in a monostatic mode or, alternatively, to a separate antenna when operating in a bistatic mode, receives a return signal from a target object resulting from the probe signal. Magnitude and phase information corresponding to the object are measured and stored in a memory at each of the center frequency steps. The range to the object is determined using the magnitude and phase information stored in the memory. The present invention provides for high-resolution probing and object detection in short-range applications. The present invention has a wide range of applications including high-resolution probing of geophysical surfaces and ground-penetration applications.

Abstract: A method of improving data obtained by radar by interpolation over frequency bands jammed by narrow-band interference, at which the following steps (A)-(J) are carried out. (A) It is determined what frequency values are affected by narrow-band interference. (B) Every radar return which is continuously connected in time and represented by a time-discrete real or complex signal f(t.sub.i), containing N sample, i=1, 2, . . . , N, is Fourier-transformed into a frequency-discrete function F(.omega..sub.i), given by N sample. (C) A series of integers N.sub.1, N.sub.2, . . . , N.sub.M is fixed, such that 1.ltoreq.N.sub.1 <N.sub.2 < . . . <N.sub.M <N. (D) The signal processing device sets F.sub.k (.omega..sub.i)=H.sub.k (.omega..sub.i) within intervals having narrow-band interference. (E) H.sub.1 (.omega..sub.i) is equated to 0 and H.sub.k (.omega..sub.i) for k.gtoreq.2 is constructed according to the following steps (F)-(H). (F) F.sub.k-1 (.omega..sub.

Abstract: A high-order synthetic aperture radar (SAR) autofocusing method decomposes phase error into basis function components, one order at a time. Image patches are partitioned into a plurality of subapertures in accordance with positive- and negative-going slope of the basis function at each order. A positive mask is applied to each subaperture within which the basis function is increasing in slope, whereas a negative mask is applied to each subaperture within which the basis function is decreasing in slope. The results are then correlated to obtain a focused image, with the principle of map-drift preferably being used to compute phase-amplitude weights. The method may be uniformly applied, enabling the steps to be performed at a plurality of increasingly higher orders without performance degradation.

Abstract: The sensitivity of a synthetic aperture radar (SAR) system employing stretch processing is improved in the presence of radio-frequency interference (RFI). The sequence of data processing operations initially uses a high number of bits to digitize radar echoes plus RFI, then uses floating-point arithmetic to perform range deskewing to "compress" RFI tones, followed by threshholding and nulling the primary RFI contributors, and finally re-quantizes the resulting radar signal to a lower number of bits and appropriately allocating these bits over the range of signal levels.

Abstract: A localized interference nulling preprocessor for a Fast Fourier Transform (FFT) or a Butler matrix system includes a means for forming a dot product of a signal vector and each of the preprocessed eigen vectors of the virtual interference covariance matrix of a predetermined localized interference, means for scaling the conjugate of the principal eigen vectors by the dot product, and means for subtracting from the signal vector the product of each dot product and conjugate of principal eigen vectors to generate a preprocess signal vector modified to produce a localized nulling of predetermined localized interference by a Fast Fourier Transform (FFT) or Butler matrix system.

Abstract: A non-invasive imaging system for analyzing engineered structures comprises pairs of ultra wideband radar transmitters and receivers in a linear array that are connected to a timing mechanism that allows a radar echo sample to be taken at a variety of delay times for each radar pulse transmission. The radar transmitters and receivers are coupled to a position determining system that provides the x,y position on a surface for each group of samples measured for a volume from the surface. The radar transmitter and receivers are moved about the surface, e.g., attached to the bumper of a truck, to collect such groups of measurements from a variety of x,y positions. Return signal amplitudes represent the relative reflectivity of objects within the volume and the delay in receiving each signal echo represents the depth at which the object lays in the volume and the propagation speeds of the intervening material layers.

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 method of classification of a device by recognizing distorted signals, generally a RF antenna pattern, emanating therefrom wherein a trainable recognition system, preferably a neural network, is provided. Known distorted signals are applied to the trainable recognition system to train the recognition system to recognize individually each of a plurality of different signals having distortion therein. Unknown distorted signals are then provided emanating from a remote device and the unknown distorted signals are then used to classify the remote device by analyzing the received unknown distorted signals in the trained recognition system. The steps of training and classifying each include the step of converting the signals from the time domain to the frequency domain. The steps of training and classifying also can each include the step of down sampling the frequency domain signals to compress the signature content.

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: An imaging system for analyzing structures comprises a radar transmitter and receiver connected to a timing mechanism that allows a radar echo sample to be taken at a variety of delay times for each radar pulse transmission. The radar transmitter and receiver are coupled to a position determining system that provides the x,y position on a surface for each group of samples measured for a volume from the surface. The radar transmitter and receiver are moved about the surface to collect such groups of measurements from a variety of x,y positions. Return signal amplitudes represent the relative reflectivity of objects within the volume and the delay in receiving each signal echo represents the depth at which the object lays in the volume and the propagation speeds of the intervening material layers. Successively deeper z-planes are backward propagated from one layer to the next with an adjustment for variations in the expected propagation velocities of the material layers that lie between adjacent z-planes.

Abstract: A broadband gigahertz frequency range radio receiver useful in electronic warfare and other applications for incoming signal detection and identification purposes. The receiver is based on Fourier transform examination of incoming signal characteristics and provides real time accomplishment of these tasks by way of using a simplified one-bit digital representation of the incoming signals and a resulting reduction of the computational load associated with the Fourier transform operation. The receiver precedes the Fourier transform operation with signal processing which may include, for example, a limiting amplifier and two bandpass filters. Two incoming signal accommodation is provided, a characteristic which is particularly improved over the characteristics of popular presently used receivers in this field.

Abstract: A CW radar range measuring system having a transmitter adapted to transmit a continuous wave radar signal phase encoded in accordance with a code and a receiver adapted to receive a radar return from the transmitted radar signal. The receiver includes an analog to digital converter section for converting a sequence of samples of the radar return into a corresponding sequence of digital words. A digital correlator/integrator is fed by the digital words and the code for providing an indication of radar return energy as a function of range from the transmitter. A processor is fed by the digital correlator/integrator for determining, from the indicated energy, target range. The system includes a frequency spectrum analyzer for determining a frequency spectrum of the digital words and wherein the processor determines the target Doppler frequency from such determined frequency spectrum.

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: An iterative process to determine the wavelet function and combination of ales of the function which provides data where there is a large separability compared to the separability of the data set prior to processing. Wavelets are selected for inclusion in a library in accordance with predetermined criteria and then applied to a digitized signal by convolution to perform digital filtering. The convolution of each wavelet is performed for the number of times dictated by the coefficients of the wavelet for each of the input signal samples. Separability of the wavelet implemented digital filtration is calculated as a percentage for each wavelet. The separation data is stored in memory until the iterative process is applied to all wavelets. The separability data is then examined to identify the wavelet producing the greatest separation. The data separability is estimated using a likelihood ratio after the probability densities for each of two sets of profile data are estimated.

Abstract: Receivers 14 and 16 comprise mixers 14b and 16b for mixing reception signals of receiver antennas 14a and 16a with a transmission signal to generate beat signals B1 and B2, respectively. Signal processing section 20 performs the Fourier transformation of beat signals B1 and B2 supplied from receivers 14 and 16 to obtain the phases of beat signals B1 and B2 and then obtain the azimuth based on the difference of these phases.

Abstract: Beat signals of respective receiver channels CH1 and CH2, produced by mixing their receiving signals with a transmission signal, are subjected to Fourier transformation to detect the frequency and phase of peak frequency components in both an ascending-section where the frequency of the transmission increases and a descending-section where the frequency of the transmission decreases. Based on peak frequency components derived from the same target, phase differences .DELTA..phi.u(i) and .DELTA..phi.d(j) between receiver channels CH1 and CH2 in the ascending- and descending-sections (steps 210-230). Relative relationship between the transmission signal and the receiving signal is judged based on the signs of the phase differences. Respective peak frequencies fu(i) and fd(j), detected as absolute values of frequency differences between the transmission signal and the receiving signal, are given sings in accordance with the judgement result.

Abstract: To measure the speed of a body (1) moving relative to the ground (2) by means of a broad-band Doppler radar (3) fixed to the moving body, two incident radar waves are transmitted successively towards the ground at instants that are close together, and the corresponding reflected waves are picked up, the frequency of at least the first incident wave being time-varying, the signals representative of the first incident and reflected waves are multiplied together, a spectrum is determined for the low frequency component of the product of said two signals, the same operations are performed for second incident and reflected waves, then two peaks that correspond with a certain amount of frequency shift in the two spectra are identified, and the speed of the moving body is determined as a function of the frequencies of these two singular points and as a function of the height of the radar relative to the ground.

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 coherent radar receiver that has pulse-to-pulse coherence using an unlocked voltage controlled oscillator, such as a Gunn voltage controlled oscillator. The present invention is a W-band, for example, bistatic receiver that uses a scanning sum channel antenna to scan the target, a downconverter for downconverting received alternating sum and difference pulse echoes from the bistatic illuminator to provide video signals, and processing circuits for processing the downconverted the video signals to precisely locate the null position on the target. A Fourier transform circuit, magnitude detector and a peak detection and centroid circuit are used to generate a voltage frequency control output signal that is applied to the voltage controlled oscillator or local oscillator that controls its frequency. An angle estimation algorithm is used that processes the video signals to locate the null offset from the center of a scan pattern generated by the antenna.

Abstract: A delay compensated Doppler radar altimeter which eliminates the relative delay curvature associated with the energy reflected by a scatterer located in the along-track direction of an aerial platform for which a most accurate estimation of scatterer elevation is desired. By Doppler shifting each return, the range indicated for each scatterer over its illumination history is equal to the minimum range x.sub.h experienced when the relative velocity between the aerial radar and the ground is effectively zero. Compensating each signal so that its entire along-track history can be used for elevation estimation leads to an advantage of more than 10 dB in gain improvement over existing systems, and less degradation from surface topography.

Abstract: This invention generates a radar analog of the optical hologram by recording a radar image in the range/doppler plane, the range/azimuth plane, and/or the range/elevation plane according to the type and application of the radar. The invention embodies a means of modifying the range doppler data matrix by scaling, weighing, filtering, rotating, tilting, or otherwise modifying the matrix to produce some desired result. Specific examples are, removal of known components of clutter in the doppler frequency spectrum by filtering, and rotating/tilting the reconstructed image to provide a view not otherwise available. In the first instance, a reconstructed image formed after filtering the Fourier spectrum would then show a clutter free replication of the original range/PRI object space. The noise `floor` can also be modified such that only signals in the object space that produce a return signal above the `floor` will be displayed in the reconstructed image.

Abstract: An FM-CW radar which is suitable for automotive anti-collision systems, for example, is provided. This radar outputs a radar signal in the form of a triangular wave whose frequency is increased at a given rate and decreased at a given rate. A receiver receives a wave reflected from a target to produce a beat signal and takes the Fourier transform of the beat signal to determine peak frequency components thereof showing peaks in a frequency spectrum. The receiver also determines phases of the peak frequency components and selects at least one from the peak frequency components in a frequency-rising range wherein the frequency of the radar signal is increased and at least one from the peak frequency components in a frequency-falling range wherein the frequency of the radar signal is decreased which show substantially the same phase to pair them for determining the distance to and relative speed of the target based on the frequency of the paired peak frequency components.

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 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 quality of wind profiling radar data is evaluated by comparing the probability density function of the power density of sets of returned samples to an exponential function. The standard deviation of individual samples from the exponential function can be evaluated to identify possible sources of contamination of the wind profiler data.

Abstract: The blade flash signature in a radar return is enhanced and used to detect and classify helicopter targets. The radar return of a target is fast Fourier transformed 34, and the frequencies corresponding to DC and the body of the target are filtered out 38. The filtered signal is inverse transformed 44, moving averaged 52, and auto-correlated 54. Auto-correlation 54 may take place in the frequency domain. If there are significant peaks in the auto-correlation output (other than at zero time delay), then a helicopter is present. The time delay between peaks is the period of the blade. The height of the peak indicates whether it is the main blade or the tail blade which has been detected, and allows a signal indicating both periods to be output. The main blade period and the ratio of the period to that of the tail blade can be compared with a data base to classify the helicopter.

Abstract: In systems wherein signal compression is performed using matched filters or transforms, as in the case of radar, multiple extrapolations are used to resolve beyond the limits of defraction. In one example, development of the method begins with a complex, uniformly weighted SAR or inverse SAR signal represented by a rectangle function. After performing an FFT, adaptive sidelobe reduction is carried out followed by an inverse weighting and truncation, after which the original signal is used to replace the center portion of the extrapolated signal. The signal is again transformed and sidelobe reduced, and inverse weighting and truncation are again performed, followed by the original data replacement step. The extrapolation procedure may be repeated end times, extrapolating each time by a factor K for a total extrapolation factor of K=k.sup.n.

Abstract: A process for collecting phase and amplitude calibration data for an active array system without the use of external sensors. The relative phase and amplitudes of adjacent T/R modules are determined when viewed through the entire array system. The calibration process involves collecting and storing these phases and amplitudes for future use. A pulse-to-pulse phase or amplitude modulation mode is employed. An element is commanded into this mode to separate its signal (in frequency) from competing signals and leakages from the surrounding modules. A T/R inversion command allows for a single element to be switched to a transmit state while the remainder of the array is in the receive state. This provides for a reference signal during receive calibration, and for single module testing during transmit calibration.

Abstract: An interferometric Synthetic Aperture Radar (SAR) system having a special-purpose processor to integrate motion compensation, interferogram coregistration, and a spectral shifting for optimal interferogram correlation together to achieve efficient, accurate, and robust three-dimensional imaging. A simple radar mapping coordinate system is implemented in the present invention to enhance the overall image processing and in particular to improve the accuracy and efficiency. The present invention substantially improves the fidelity and efficiency of phase unwrapping by incorporating phase-bootstrapping process, a correlation filter, and other processes. Absolute phase determination is implemented without known ground references by two proposed techniques employing cross-correlation of sub-patches to generate a number of estimates within a patch and weighting correlation processes.

Abstract: The invention pertains to a hand-held or vehicle mountable portable procer based high resolution radar system for detecting and identifying an object by using high resolution radar. In particular, the invention concerns using radio waves for identifying a depth and material of an object within a media. This system can perform target and media identification in real-time. This process is achieved by the system's processor where the media identification results can be visually displayed on an output unit. The generated carrier signal used in the radar system is an exponentially decaying superimposed direct and alternating signal. The frequency of the carrier signal can be in the microwave region. The system performs analog to digital (A/D) conversion using integrated circuitry whose sampling rate is in the same as the carrier signal transmission rate.

Abstract: A cost-effective FMCW radar equipment has a digital signal processor which controls at least one antenna through an oscillator and produces a mixed signal from transmitted and received signals modulated with a triangular waveform. The mixed signal is subjected to Fast Fourier transformation for each modulation phase (up and down) of each measurement cycle in order to obtain object frequencies, which are assigned to each target object, from the determined maxima. Object tracks which are formed from the object frequencies extend back over a plurality of measurement cycles and are used to form estimated values for those measured values of the object frequencies which are to be expected in the next measurement cycle. The mutually associated object frequencies of both modulation phases of a measurement cycle are determined and the distance and relative speed of each target object are determined from them.

Abstract: The present invention discloses a system for extracting targets from radar signatures. Disclosed is a unique combination of Wavelet technology and neural networks using fractal geometry techniques that estimates the Fractal Dimension of a target even in the presence of high background noise.