Abstract: A monopulse thresholding processor and method for improving resolution by using the difference channel data to eliminate "excess" sum channel returns. The processor may be used with a radar system that comprises an antenna, a transminer, a receiver for processing transmitted radar signals to produce radar returns therefrom, a log compressor for converting radar returns to log values, and a display for displaying the radar returns. The signal processor comprises a left sum and right sum generator coupled to the receiver for computing a left sum and a right sum from radar returns generated by the receiver. A pseudo-difference generator is coupled to the left sum and fight sum generator for generating pseudo-difference channel data. A beam sharpener is coupled to the left sum and right sum generator and to the pseudo-difference generator for beam sharpening the radar returns.

Abstract: A terrain height radar system and processing method comprising a high resolution synthetic aperture radar (SAR) mounted on an air vehicle and a SAR signal processor containing a signal processing algorithm or method for computing terrain height and radar backscatter power. The system contains motion sensing and navigation functions that also provide data to the signal processor to provide motion compensation. Signal processing algorithms in the method compensate for planar motion of the air vehicle for variations of terrain height in the field of view. The algorithms also compensate for nonplanar motion of the radar, and for scatterers in or very near to a reference plane in the field of view. The algorithms exploit defocusing due to displacement from the reference plane to estimate the terrain height above the reference plane. The algorithm is computationally efficient because the bulk of the radar signal processing is common to both the SAR function and the terrain height estimation function.

Abstract: A distant target vibration assessment and signature determining apparatus for operation from a vibrating platform such as an aircraft or helicopter. The disclosed system employs pulse illumination of the distant target and of nearby atmospheric aerosol particles and uses the latter illumination derived signal as a characterization in reverse of the vibrations of the sensor's mounting platform. The nearby and distal nature of the two illuminated energy reflections enables their range gated segregation and individual transformation into the frequency domain. Frequency domain vibration signatures of the distant target and the vibrating platform are then individually obtained and subtracted in order to obtain a clean vibration spectrum representation of the distant target. Variations of the system including a two pulse operating cycle, the use of signal strength evaluation and signal processing alternatives are also disclosed.

Abstract: An MTI radar based on a comparison of the Doppler shifts of the original signal and a phase-reversed signal using pulse compression wherein the received signal is phase detected for in-phase and quadrature components relative to the IF. A Doppler-corrected pulse compressor produces a magnitude signal for the Doppler shift of the received signal from the sequence of in-phase and quadrature components. Another Doppler-corrected pulse compressor produces a magnitude signal for the Doppler shift of the received signal from the conjugates of the sequence of in-phase and quadrature components. The magnitude signal of the same Doppler shift of the two compressors are compared and the difference is the output of the MTI.

Abstract: A frequency discriminator which generates an output signal characteristically representative of a predetermined frequency spectrum of an input signal, but insensitive to variations in the amplitude and spectral width thereof is disclosed. The frequency discriminator is adaptable for use in a radar receiver clutter tracking loop to improve the filtering of clutter signals from the radar returns by maintaining a measured centroid frequency of the clutter signal spectrum substantially at a desired frequency with a loop response which is invariant to both amplitude and spectral width of the clutter signals. More specifically, the frequency discriminator when included in a clutter tracking loop of a radar receiver discriminates from the clutter spectrum a plurality of frequency signals in accordance with a preselected sequence and computes the amplitudes thereof to generate a corresponding sequence of amplitude signals.

Abstract: The present invention relates to a method and apparatus for producing compensated baseband signal components for a moving radar antenna. A fixed frequency oscillator is used and a baseband signal is complex multiplied by a time dependent multiplicand to produce a signal free of overlap convolution so that clutter signal components are centered around the Doppler frequency f.sub.D =0. Consequently, target detection is as easy as for a stationary radar antenna.

Abstract: A signal detection system, preferably for use with a coherent radar system elects certain combination of input signal samples in a block of signal samples to derive a test statistic which is unbiased by Gaussian noise. Products of pairs of sample values are stored in a data sample look-up table. An index look-up table is created by scanning through possible combinations of addresses and excluding those combinations of sample values which would be redundant over other combination and would result in a contribution to biasing by noise. Pairs of addresses from the index look-up table are then used in sequence to access first and second products from the data sample look-up table. The first product is multiplied by the complex conjugate of the second product and the (quadruple product) result is averaged to form a test statistic which is insensitive to position and constant velocity. Detection of the signal is determined by testing the real part of the averaged test statistic against a threshold.

Abstract: In a monopulse radar processor, the usual sum (s) and difference (d) signals are manipulated to produce two other signals (s+ad and s+bd, in which a and b are constants). The phase of each of these derived signals with respect to the sum signal is then determined. The real part of d/s and, if desired, the imaginary part of d/s are calculated from these measured phase angles. The real part of d/s is the conventional output from a monopulse processor.

Abstract: A conical scan radar system (10) provides return pulses (30) to an A/D converter (38) from which a shaped pulse train is received and stored in a FIFO memory (40). The stored pulse train is then passed through first and second finite impulse response filters (42,44) for achieving sampling rate reduction prior to rendering via a programmable signal processor (64) of target detection identification and tracking.

Abstract: A radar target velocity estimator apparatus and method for computing a radial velocity of radar targets from differences in Doppler frequency shift between pulse-returns of multi-pulse waveforms. The velocity estimator uses Doppler frequency shift which is obtained from a finite impulse response (FIR) filter in combination with logarithm tables stored in read-only-memory (ROMs) to calculate the target's velocity. The estimation process requires the calculation of each complex FIR filter value twice during a pulse repetition interval; once for returns of a leading set of radar pulses and then for a trailing set. The estimated velocity is proportional to the phase difference between each corresponding pair of filter values. The estimate is a function of the arctangent of the quotient of the in-phase component of the complex value divided by the quadrature component.

Abstract: A method of correcting phase and amplitude imbalances of I and Q components using digital correction coefficients. The amplitude Gc and phase coefficient Pc obtained solely in the time domain from a pilot signal. The I and Q components of the pilot signal are sampled over at least one integer cycle after which the number of samples taken during an integer number of cycles is determined for the samples of the component with the steepest slope. The sums of self and cross products are used to calculate the coefficients.

Abstract: In a method for tracking a radar target the imaginary part of the complex elevation error signal is utilized and the value of the complex elevation error signal is calculated for a plurality of frequencies in a repeated sequence. The value change between the different frequencies is used for determining the position within an unambiguous interval and the values calculated at the zero crossing are utilized as measure of the inclination which in turn is compared with inclinations calculated for zero crossings in a general case, whereby a single-valued (unambiguous) interval and position can be determined and thereby the associated elevation angle or target height can be calculated. The method is specifically useful for tracking at low height where multi-path propagation poses a problem in tracking according to known methods.

Abstract: A method and apparatus for classifying objects based upon information conned in the fourth order cumulant derived from energy from the object. Successive pulse returns in active systems and samples in passive systems are converted into vectors based upon the fourth order cumulant information for each successive return or sample. The vectors for each such pulse are compared to corresponding class information based upon the corresponding fourth order cumulant information. The comparison uses loglikelihood ratios of the different pairs of classes. Decision making is based upon the value of each loglikelihood ratio in comparison with a class threshold.

Abstract: A digital signal processor optimized for synthetic aperture radar image formation provides two separate stages of arithmetic processing along independent in-phase and quadrature channels. The first stage accepts a first reference input and integrates a multiplier/accumulator for each channel, and the second stage accepts a second reference input and includes a multiplier and an adder for each channel. In addition to hardware to select and route data in accordance with a desired operation, a hold register is incorporated prior to input-selection logic to facilitate complex-by-complex multiplications of data derived from either input in the first stage. Hold registers are also included before the second-stage adders to permit a complex multiplication with magnitude weighting to occur during the zero-th stage of a fast Fourier transformation, effectively hiding the time to perform one FFT stage.

Abstract: A stepped frequency ground penetrating radar system is described comprising an RF signal generating section capable of producing stepped frequency signals in spaced and equal increments of time and frequency over a preselected bandwidth which serves as a common RF signal source for both a transmit portion and a receive portion of the system. In the transmit portion of the system the signal is processed into in-phase and quadrature signals which are then amplified and then transmitted toward a target. The reflected signals from the target are then received by a receive antenna and mixed with a reference signal from the common RF signal source in a mixer whose output is then fed through a low pass filter. The DC output, after amplification and demodulation, is digitized and converted into a frequency domain signal by a Fast Fourier Transform.

Abstract: BPSK signals are detected by receiving an input signal containing the BPSK ignals to be detected, by means of a compressive receiver; applying the receiver output to a 90.degree. phase shifter which outputs a phase-shifted signal; applying the phase-shifted signal to a delay line which applies a further phase shift of -180.degree. to the phase shifted signal; and detecting the relative phase of the non-phase-shifted signal from the compressive receiver and the phase-shifted signal from the delay line by applying those signals to respective input ports of a phase detector, the output of the phase detector being indicative of detection of a BPSK signal. Advantageously, zero-crossings of the output signal of the phase detector are detected, and the output of the zero-crossing detector is low-pass-filtered.

Abstract: An AWTSS is shown to be made up of an improved synthetic aperture radar (SAR) for generating radar maps with various degrees of resolution required for navigation of an aircraft and detection of ground targets in the presence of electronic countermeasures and clutter. The SAR consists, in effect, of four frequency-agile radars sharing quadrants of a single array antenna mounted within a radome on a "four axis" gimbal with a sidelobe cancelling subarray mounted at the phase center of each quadrant. Motion sensors are also mounted on the single array antenna to provide signals for compensating for vibration and stored compensating signals are used to compensate for radomeinduced errors. In addition, a signal processor is shown which is selectively operable to generate radar maps of any one of a number of desired degrees of resolution, such processor being adapted to operate in the presence of clutter or jamming signals.

Abstract: A method and apparatus that uses iteration to achieve a better prediction of the values of the commands needed to balance the gains of .SIGMA.+.DELTA. and .SIGMA.-.DELTA. channels of a radar guidance system, when an imbalance occurs due to a change caused by the AGC circuitry. An improved method of measuring channel-to-channel gain imbalance versus AGC measurements is provided, which produces modified input values that are used as commands that correct the mismatch during missile flight so that residual error is minimized and more accurate guidance is achieved. The present method is implemented by measuring the gain imbalance at predetermined AGC points during system calibration, and iterating these measurements to produce a relatively small channel-to-channel gain imbalance at the .DELTA.AGC amplifiers. The measured imbalance is then converted to .DELTA.AGC commands and applied to the .DELTA.AGC amplifiers. The resulting gain imbalance is measured and this value is added to the originally measured value.

Abstract: A system for distinguishing between a target and clutter analyzes frequency components of returned wave energy by one or more networks each having inputs receiving successive samples of the returned energy and having outputs individually connected to the inputs through multiplier elements providing selectable factors. The multipliers corresponding to each output are connected to the output through a summing element and a selectable and generally sigmoidal activation function. The factors may be bandpass filter coefficients or discrete Fourier transform coefficients so as to generate frequency components of the energy. Predetermined frequency characteristics of the returned energy may be detected by providing the outputs of a network to a network in which the factors are selected as correlation or convolution coefficients, are selected to integrate fed back outputs, or are selected to sum several outputs within a predetermined range.

Abstract: A transmitting and receiving part of a pulse Doppler radar, in which the transmitting oscillator, by frequency shifting, is at the same time used as a local (reception) oscillator, and the intermediate-frequency reference frequency is generated coherently with respect to the pulse repetition frequency. Since only one high-frequency oscillator is required, the quality of which does not have to meet very high requirements, a low-price pulse Doppler radar can be implemented.

Abstract: A system for detecting phase and gain imbalance errors in a synchronous detector. The synchronous detector (10) is assumed to have a fist circuit (16) for providing a first signal representing a first sinusoidal term (e.g., a cosine term) and for providing a second signal representing a second sinusoidal term (e.g., a sine term) complementary to the first sinusoidal term, circuitry (12) for mixing an input signal with the first signal and circuitry (14) for mixing the input signal with the second signal. The system (16) for detecting phase and gain imbalance errors of the invention includes an amplitude compensation circuit (24) for detecting and correcting amplitude errors in the first and second signals and a phase compensation circuit (26) for detecting and correcting phase errors in the first and second signals. For amplitude compensation, the outputs of the amplitude and phase compensation circuits are input to first and second amplitude detector circuits (28) and (30).

Abstract: A system for demodulating and decoding differential phase shift keying (DPSK) transmissions utilizes a bandpass filter, an analog to digital converter and a digital signal processor. Removal of the effects of unknown frequency component is achieved by applying a complex phase correction/rotation factor after DPSK demodulation. The actual phase of the complex signal is never computed directly. All of the processing from Rader decomposition through carrier tracking filter is performed on the complex values and therefore requires only multiplication and addition operations which can be performed at high speed in a microcomputer or in dedicated arithmetic hardware.

Abstract: The disclosed system comprises a testing system which measures the stability of a moving target indicator radar transmitter. It automatically measures the imperfections of its internal in-phase (I)/quadrature (Q) demodulator, and it consists of a control computer, a synchronizer, a frequency synthesizer, an IQ demodulator, a low noise amplifier and a waveform recorder. A unit under test is inserted across the test set for measurement and calibration. The system set has the following features: (a) An automatic calibration routine that requires a tunable RF source. This source provides the RF drive to the UUT. (b) A discontinuous analog to digital (A/D) sample clock that has a precise controllable relationship with the RF pulse. The A/D sample clock samples only during the presence of the RF. (c) A method for computing stability using a table of amplitude and phase weighting coefficients and pulse positions. This table is generated by the user and any desired combination of values is possible.

Abstract: A method and apparatus for electronically simulating the transmit-receive gnal path of doppler radar during a target encounter in a simulator. It is an end-to-end fuze (radar) test from RF "in" to video "out". Target signature data is collected at a reduced relative encounter velocity from the actual target. The modified pulse doppler radar produces two orthogonal signals which define the complex received radar signal. These signals are then recorded. The missile radar to be tested is coupled to the simulator which simulates an actual missile to target encounter. During the test the PROMs are clocked into RF components in an RF Loop and clock counter is started. When the radar threshold is exceeded, a radar video output function stops the counter. By correlating the number of clock pulses counter to the distance marks traveled along the missile trajectory, missile radar function with respect to target location data is obtained and missle lethality computed.

Abstract: A sensing circuit is assumed to produce in phase and quadrature Doppler signals. The relative phase of these signals is used to determine the passage of object such that correctly related zero passages in the two signals are counted, and the count state within certain periods of time yields information to check the significance of signals as genuine Doppler signals.

Abstract: A radar processor is described which performs acceleration compensation for accelerating targets. A set of matched filters is formed that compensates for each one of a predetermined set of target accelerations. The matched filters optimize the signal-to-noise ratio by weighting and combining the Doppler filters over which the target is spreading. As a result, enhanced detection capability of maneuvering targets that spread their energy over Doppler filters is provided. Radar processor loading is reduced, thus making practical the implementation of long coherent arrays.

Abstract: A system and method for correcting a gain and phase imbalance between I and Q channels of a synchronous detector. The method of the invention includes the steps of: a) inputting a signal into the detector and extracting therefrom a received signal and a corresponding image signal; b) inputting the received signal in a first Doppler filter; c) inputting the image signal in a second Doppler filter; d) forming a first discriminant; e) forming a second discriminant; f) computing phase (.phi.) and gain (.rho.) errors from the first and second discriminants; g) calculating first and second correction factors based on the phase and gain errors; and h) using the correction factors to correct the phase and gain imbalance errors.

Abstract: A gain control network having a phase splitter circuit responsive to an RF input signal for providing first and second RF signals that are out of phase relative to each other, a first series of switched gain control elements, and a second series of switched gain control elements substantially identical to the first series and commonly controlled therewith. The first series of gain control elements is responsive to the first RF signal for providing a first gain controlled signal, and the second series of switched gain control elements is responsive to the second RF signal for providing a second gain controlled signal. A phase combining circuit combines the first and second gain controlled signals to provide a gain controlled RF output. By performing gain control with two gain control channels having substantially identical circuits and common switching control, transient glitches in each of the channels are substantially identical and are substantially cancelled via the phase combiner.

Abstract: Electronic antenna-rotation compensation apparatus is provided for correcting data errors introduced into radar return signals by the rotation of phased array antennas. The apparatus includes circuitry for sampling and A-to-D converting I (in phase) and Q (quadrature) radar return signal components provided by individual antenna elements comprising the array antenna and for providing and applying correction factors to each ith signal components sample from each nth element across the antenna. The correction factors may be precomputed and stored in a memory for use when required or may be computed as needed. The corrected, digital I and Q signal component samples are supplied to a conventional processor, for example, as adaptive array processor, for extracting useful target data from return signal interference and clutter. A corresponding method is provided for compensating for the effects of phased array antenna rotation.

Abstract: A multistage estimator is provided for the parameters of a received carrier signal possibly phase-modulated by unknown data and experiencing very high Doppler, Doppler rate, etc., as may arise, for example, in the case of Global Positioning Systems (GPS) where the signal parameters are directly related to the position, velocity and jerk of the GPS ground-based receiver. In a two-stage embodiment of the more general multistage scheme, the first stage, selected to be a modified least squares algorithm referred to as differential least squares (DLS), operates as a coarse estimator resulting in higher rms estimation errors but with a relatively small probability of the frequency estimation error exceeding one-half of the sampling frequency, provides relatively coarse estimates of the frequency and its derivatives.

Abstract: A phase detector receives two input digital signals representing Cartesian coordinates of a vector and outputs a digital signal indicative of the phase angle of the vector. The input digital signals are logarithms of the square of, for example, in-phase and quadrature components of a radar signal and are subtracted in the phase detector to produce a difference signal having a magnitude and a polarity. The polarities of the difference signal and the two information signals are used to determine the octant of the phase angle by addressing a read only memory. The magnitude of the difference signal is used as an address of a read only memory storing digital values corresponding to angles within an octant. The octant output by the first read only memory and the angle output by the second read only memory together indicate the phase angle of the vector.

Abstract: A method and correction circuit is described incorporating a monopulse receiver, injecting a first signal of known amplitude and arbitrary phase and a second signal of the same amplitude shifted 90.degree. and measuring the output voltages of the channel and using the measurements to generate four coefficients which may be mathematically applied to the ouptut signals of the channel to provide a corrected output. The invention overcomes the problem of compensating for phase and gain drift in the in-phase and quadrature paths of the sum and difference channels of a monopulse receiver.

Abstract: A CW radar comprises a substantially continuously operable transmitter (10) and receiver (16,18,20), signal operating means (12,14) for radiating the transmitter signal and for receiving at least the return signal and a reflected power canceller (RPC) circuit (26, 28 and 30) for cancelling leakage signals in a signal path from the signal operating means to the receiver. The receiver front end comprises quadrature related mixers (18,20) which supply intermediate frequency signals (I.sub.1 and Q.sub.1) to a low frequency control loop (32, 34, 36) which supplies at least a pair of control signals (I.sub.c, Q.sub.c) to a four quadrant vector modulator (28) in the RPC circuit. In order to be able to optimize the cancellation of phase as well as amplitude, the control circuit loop includes means for suynthesizing control vectors (I.sub.1 -I.sub.1, Q.sub.1 and -Q.sub.1) from the outputs of the quadrature related mixers (18,20).

Abstract: A moving target detector (MTD) in a radar system uses corrected weighting coefficients to compensate for pulse stagger effect on transmitted pulses. Transmitted pulses are sampled when the radar is switched to a test mode for determining a correction factor which is used to calculate the corrected weighting coefficients. The radar return signals are processed in the MTD by a finite impulse response (FIR) filter using the stored corrected weighting coefficients calculated for each sequence of transmitted pulses including block stagger and pulse stagger sequences.

Abstract: A device for computing a nonrecursive and sliding discrete Fourier transform as applicable in particular to processing of a pulse compression radar signal has N identical and parallel stages (E.sub.k) for receiving in each case samples of the input signal (e.sub.m+N). Each stage comprises two complex rotation operators, two adder-subtracters and two delay circuits and delivers a signal X.sub.k.sup.

Abstract: With a frequency-agile pulsed doppler radar with high pulse repetition frequency (HPRF) in the unambiguous velocity region, in order to measure the range of a target the complex time signal derived from the echo signals of a coherent processing interval (CPI) is transformed into the frequency domain, the transformed spectrum is multiplied by a bandpass function with a mean frequency coinciding with the doppler frequency of the target, and the product is transformed back into a time signal. The real envelope of this re-transformed time signal displays a definite leading edge and a steady state region, from which the echo travel time can be estimated. Particular advantages may be derived for the pulsed doppler radar set from a plurality of frequency agile transmitter/receivers operated at the same time at different frequencies, and whose frequency switching times are time-staggered.

Abstract: Video signals delivered by a side-looking radar system during M successive recurrences in each section of a sweep range are sampled, coded and registered in the form of a series of samples of modulus .rho..sub.i and a series of samples of phase .phi..sub.i. The device performs the correlation with a series of samples .theta..sub.

Abstract: An improved radar is disclosed wherein an array of digital numbers describing a target area is produced. The numbers have values representing differences in ranges between the radar and reflecting points in an area on the ground illuminated by the radar. The values also represent the differences in angles between the radar and the reflecting points.

Abstract: A discrete fourier transform direction finding apparatus for performing a direction finding function on signals received through two antennae separated by a known distance. The outputs of the respective antennae are connected to first and second receiver channels which convert the received signals down to baseband and provide orthogonal I and Q channel outputs. A common local oscillator is used to maintain phase coherency between the channels and AGC signals are provided to maintain identical delays in the receiver RF paths. The processed signals from each receiver channel are than fed into a respective charge coupled device Chirp-Z transform (discrete fourier transform) circuit to produce real and imaginary components of the received signals. These signals are then converted to digital form and are used by subsequent circuitry to determine the angle of arrival of the received signal.

Abstract: A method of and an arrangement for the combined correction of I/Q phase and amplitude imbalances within channels and interchannel phase and amplitude mismatches in arrays of signal channels. The I and Q channels of a reference channel are orthogonalized while simultaneously commencing the correction of an auxiliary channel. Optimum correction is obtained with reduction in hardware in comparison with a cascaded correction method, the auxiliary channel I and Q components being transformed only once.

Abstract: A multichannel processor for signals modulated onto a common IF frequency includes first and second analog-to-digital converters (ADC) for first and second channels, respectively. Each ADC receives a 4XIF frequency clock for producing digital samples, which are applied to a pair of gates for alternately coupling the digital signal to two signal paths. Each signal path alternately negates and does not negate the signals passing therethrough, thereby generating baseband I and Q signals for that channel. Since each channel has a separate ADC, there may be amplitude and temporal error between the channels. One of the channels is selected as a reference, and uses a pair of interpolators to produce samples representing the I and Q signal values at a common time between clock pulses. The other channels include controllable interpolators which are adjusted so that their I, Q common times correspond to that of the reference channel.

Abstract: A method of high resolution imaging and identifying of targets with an Inverse Synthetic Aperture RADAR (ISAR) coupled with Adaptive Beam Forming (ABF) is disclosed. The ISAR system utilizes a pulsed RADAR transmitter and a highly thinned, dispersed phased array with random, non-colinear elements. An adaptive processor and feedback loop performs the ABF process such that high resolution of a moving target is possible. The high resolution signal allows accurate imaging and identification of the moving target.

Abstract: This invention relates generally to signal processing techniques for removing or reducing the effects of instabilities in pulsed signal sources, as in phase echo systems using a pulsed signal transmitter source, and, more particularly, to a technique for compensating for the varying amplitude, frequency and/or phase characteristics of the signal source pulses during operation.

Abstract: A method and apparatus for use in a pulse-echo imaging or ranging system comprising means (32) for identifying the analytic signal from a received signal and means (34) for extracting ranging information from the analytic signal. The analytic signal can be obtained and processed by digital or by analog circuit means. One embodiment of the analog circuit means (32) includes means (90) for modulating the received signal on a carrier frequency, means (92) for obtaining a single sideband signal from the modulated signal and means (94) for envelope detecting the single sideband signal.

Abstract: A digital poly phase pulse compressor that utilizes delay lines to separate KN samples of a received compressed pulse in I and Q channels, multiplies N of the KN samples with quadrature, weighted code phase signals by shifting and adding, cross couples the products of the shifting and adding in the I and Q channels to remove all code phase terms from the N samples in each channel, and combines the final n signals to provide I and Q compressed pulse components. The I and Q channels can be expanded into pluralities of channels to include compensation for Doppler shift.

Abstract: A phase comparator has additional circuitry for correcting nonquadrature error during operation of the comparator. The phase comparator has a 90 degree power divider which receives a reference signal input and produces two reference outputs, one shifted 90 degrees out of phase with the other. The phase comparator also has a zero degree power divider which receives a return signal, such as a reflected signal of a radar transmitter unit. The outputs of the power dividers are applied to mixers and filters to result in an I video output whose frequency is the difference between the reference and signal input frequencies, and a Q video output which is identical in frequency but shifted 90 degrees. The correction circuit includes a frequency trap connected to the reference input and tunable about a center frequency of approximately the third harmonic of the fundamental reference frequency.

Abstract: Apparatus is provided for compressing unfocused synthetic aperture radar (SAR) phase history pixel data by coupling the complex inphase phase history data output from the SAR to a first converter/compressor which produces compressed scalar log amplitude data and scalar phase pixel data. The output from the first converter/compressor is applied to a series to parallel converting means for converting plural scaler pixel data into vector data representative of a plurality of pixels. The output of the series to parallel conversion means is coupled to a second converter/compressor for converting the plural scalar pixel data into compressed encoded data representative of a plurality of pixels of unfocused SAR phase history data which is transmitted as compressed unfocused phase history data.

Abstract: An apparatus for measuring pulse compression ratio which receives a pulse compression radar signal that has been phase-modulated by a two-phase code. The apparatus comprises a means for detecting a function of the number of times of phase inversion existing in the received pulse compression radar signal to obtain the pulse compression ratio corresponding to the function of the number of times of phase inversion.

Abstract: A signal processing system in a transmitter/receiver system for reducing undesired amplitude, frequency and/or phase distortions arising due to variations from transmitter pulse to transmitter pulse. A plurality of sequential samples of transmitted pulses are averaged and a plurality of filter coefficients are determined therefrom. The coefficients are used in a plurality of filters which respond to a plurality of sequential samples of received pulses, the filters providing output signals in which such distortions are reduced.

Abstract: A device for calculating a discrete, moving window and non-recurrent Fourier transform, especially applicable to the processing of a pulse compression radar signal. The device includes N stages which, on the basis of samples of the input signal, each give a signal of the form: ##EQU1## where k is the index of the stage (O<k<N), m the index of the window and N the number of samples in the window, N being a multiple of four. The complex rotations of the expressions (1) and (3) are each broken down into a rotation in the first quadrant of the complex plane, a rotation common to N stages and a supplementary rotation specific to each stage, achieved by addition-subtraction.