Abstract: An improved MTI radar system including a signal expander/compressor for providing palindromic P2 phase-coded upswept and downswept expanded signals that are alternately transmitted by a radar transmitter. The echos from the upswept and downswept signals are received by a receiver, compressed in the signal expander/compressor and inputted to an MTI subtractor. Since the autocorrelation sidelobes of the palindromic phase coded echos are real, the echos from stationary clutter are completely cancelled so that the system is capable of detecting weak echos from moving targets.

Abstract: A technique for improving sidelobe canceller performance by blocking the canceller output signal upon sensing reduced main channel interference accompanied by an increased sidelobe canceller output. Two signal processing networks form the difference between successive output signals from a radar antenna and sidelobe canceller respectively. The difference signals are multiplied together and the product used to control passage and preclude utilization of the canceller output signal when reduced jamming interference occurs.

Abstract: A system for cancelling jammer signals entering the mainlobe of a monopulse adar and providing target locations with respect to the jammer position comprising for a sequential lobing embodiment: measuring the angular position of the jammer in the radar's mainlobe via the use of monopulse sum and difference signals, pointing the radar antenna so that the jammer is positioned within the 3 dB points of the mainlobe of the monopulse antenna, converting the sum and difference echo signals received with the antenna in this position from the next radar transmission into a second set sum and difference signals, applying this second set of sum and second set of difference signals to the inputs of an adaptive canceller to cancel the jamming signal therein and storing these signals in time sequential order, changing the orientation of the radar antenna by a small arbitrary elevation angle, converting the sum and difference echo signals received with the antenna in this new position from a third radar transmission into a

Abstract: A digital, open-loop, sidelobe canceller system includes an arrangement of uxiliary-channel preprocessing cancellers and a series of main-channel cancellers in which specific cancellers average a different number of samples for cancelling both barrage (continuous) jamming and false-target-repeater jamming, which enter the sidelobes of a radar antenna. The preprocessing cancellers and each of the main-channel cancellers, except the last succeeding main-channel canceller, use long-time averaging (averaging over a large number, n, of samples of the main and auxiliary signals, where n>>2) for removing barrage jamming from the main signal. The last succeeding main-channel canceller uses short-time averaging (averaging over approximately 2-4 samples) for removing false-target-repeater jamming from the main signal.

Abstract: A method and apparatus exploiting the discovery that the crosscorrelation of constantly spaced rows of the matrices representing certain pulse codes sum to zero. In a ranging system, such as a radar, pulses are coded according to the rows of a such a matrix, transmitted sequentially and each return processed sequentially through a filter matched to one of the coded pulses. (A different preselected filter is used for each return.) The sequence of filters is chosen so that for returns for a given range interval, each filter is matched to the returning pulse, resulting in outputs from the filters representing auto-correlations of the returned pulses. These outputs are time delayed added coherently to form the compressed pulse, and annunciated as a target hit. Should the filters and returns be mismatched, as with ambiguous stationary clutter returns, the outputs of the filters are cross-correlations which, according to said discovery, sum to zero.

Abstract: A method of preserving targets in the clear in an adaptive baseband MTI radar system with pulse compression is disclosed. The angle of the weighting signal is determined from the inverse tangent of the inphase and quadrature components of the weighting signal. This angle is then compared to a threshold angle in order to generate a modified weighting signal.

Abstract: A method and apparatus for reducing cyclic losses due to doppler shifting frequency-derived phase coded expanded radar pulses using new expanded pulse codes which increase the number of phase elements without increasing compression ratios. These new expanded codes may be generated by sampling the phase characteristics of a chirp or step-chirp waveform above the Nyquist rate to derive the phases of the new coded waveforms and compressing the new expanded pulses with a compression ratio equal to the reciprocal of the signal bandwidth.

Abstract: A digital pulse expander-compressor for use in pulse compression radars and having the advantage of precompression bandwidth tolerance. The pulse expander-compressor employs a discrete Fourier transform circuit and multi-stage delay line feeding inputs x(n) to the discrete Fourier transform circuit to generate outputs in accordance with the formulaF.sub.k =.SIGMA.x(n)exp[-jz.pi.nk/N]where n is the sequence number of the clock pulse; N is an even integer corresponding to the number of delay stages plus one and k is the number of the output subpulse from the transform circuit. An arrangement of delay stages differentially delays the output subpulses from the discrete Fourier transform circuit, and a coherent summer adds the real and imaginary parts of the signals from the delay lines. The delay stages delay the subpulse F.sub.k by nN clock pulse intervals where n and k are interrelated by the formulae k=N/2-n for n=0, 1, . . . , and N/2 and k=(3N/2)-n for n=N/2+1, N/2+2, . . . , N-1.

Abstract: A digital pulse expander-compressor for generating polyphase coded pulses which are highly doppler tolerant and have autocorrelation functions which are identical under frequency sweep reversal. The expander-compressor comprises an input expansion circuit for generating N replicas of a pulse to be expanded, a matched filter FFT with phase weights disposed in each input thereto, and phase inverters disposed in every other output therefrom, and a time dispersion circuit for appropriately adding the pulses from the FFT output to yield an expanded or compressed pulse. The phase weights to be inserted at the inputs to the FFT are determined by the equation .phi..sub.n =.+-..pi.(n-1/2).sup.2 /.rho. for a PP-3 code or .phi..sub.n =.+-.[.pi.(n-1/2).sup.2 /.rho.-.pi.(n-1/2)] for a PP-4 code, where .rho. is the pulse compression ratio and n varies from 1, 2, 3 . . . .rho..

Abstract: A method and apparatus for reducing the peak to peak-sidelobe ratio of the compressed pulse output signal of a symmetrical frequency derived phase coded pulse expander-compressor. The apparatus includes a bandwidth limiting device connected to the output of a symmetrical frequency derived phase coded pulse expander-compressor.

Abstract: The present invention preprocesses serial data sample sets so that truly ependent samples are available for further processing. Samples to be analyzed are delayed and compared in order to isolate both components that are correlated between samples, and components that are uncorrelated between samples. These components provide independent information relating the samples which are used to modify or preprocess incoming data.

Abstract: An improved technique for eliminating interference in serial data samples ving signal components which are desired to be removed before being further processed. A limited-iterative technique is employed to reduce components of the incoming data samples which are correlated among prior data samples.

Abstract: A sidelobe-canceller system for cancelling jamming interference signals f a radar signal includes serially cascaded cancellation channels utilizing preprocessing cancellers and main-channel cancellers. The last serially cascaded cancellation channel includes terminal preprocessing cancellers and terminal main-channel cancellers. The preprocessing is improved by the use of AGC circuits connected one each between the terminal preprocessing cancellers and terminal main-channel cancellers to stabilize the gain of the terminal main-channel cancellers, thus improving the cancellation ratio and transient response of the system.

Abstract: An improved FM pulse compression system which has low range-time sidelobes nd is doppler tolerant. This system is implemented by using an analog-type linear FM modulated transmission pulse and processing the echo from this pulse by means of baseband sampling at the Nyquist sampling rate and then compressing this sampled signal by means of a discrete phase compression circuit. In brief, the present invention comprises a receiver for receiving the FM echo pulse, a sampling and holding circuit for sampling the echo at baseband at the Nyquist sampling rate and then converting to IF, and a discrete phase compression circuit for compressing the appropriate number of sampled outputs from the sampling and holding circuit. If an echo is properly indexed in the phase compression circuit, then a short pulse with a relatively high amplitude is generated.

Abstract: A pulse compression system for use with step approximation to linear FM and rank coded signals to eliminate sampling errors and range time grating lobes while providing large pulse compression ratios comprising: a receiving circuit for receiving echo signals, a converting circuit for converting echo signals from the receiver to I and Q baseband signals without clock sampling, a sliding window discrete Fourier Transform or fast Fourier Transform (FFT) circuit including a taped delay line and a plurality of resistor-type phase weighting networks and adders for generating a plurality of output signals representing the different frequency steps in the signals, a delay circuit for differentially delaying the output frequency steps from the sliding window DFT circuit so the the output steps occur simultaneously, and a summer for adding the differentially delayed outputs to yield a short pulse with a peak amplitude when a coded echo pulse is correctly indexed within the delay line of the DFT circuit.

Abstract: A digital pulse compression processor for reducing the processing loss in rget-echo signals caused by sampling time errors comprising a first processing channel for sampling the echo signal in accordance with pulses from a first clock signal and a second processing channel for sampling the echo signal in accordance with pulses from a second clock signal at the same sampling frequency as the first clock signal but with its pulses interlaced, in time, approximately midway between the pulses of the first clock signal to ensure that the largest sampling error will be one-quarter of a sampling period or less. The sampled signals in each channel are then digitized and compressed, and then processed to form the compressed signal envelope. The resultant signal envelopes from each channel are multiplied together to form a low-sidelobe narrow output pulse.

Abstract: The invention is a configuration of digital open-loop cancelers, each of ch uses a batch window sampling technique, for decorrelating a main input signal from a plurality of auxiliary input signals by using one or more iterations of cancellation. The main signal includes a desirable signal and undesirable interference signals. The auxiliary signals include the undesirable interference signals which are correlated with the interference of the main signal. Samples of the main signal and a first auxiliary signal are fed to a first digital canceler. The canceler batches them, (forms the samples in a group) and measures the correlation between the main signal and auxiliary signal. This measurement, or weight, is applied to each of the samples of the auxiliary signal which were used to establish the weight. The weighted auxiliary samples are subtracted from the main input signal to produce an output residue signal that is uncorrelated with the auxiliary signal.

Abstract: A digital open-loop canceller is used to decorrelate one signal from anot in such applications as coherent sidelobe cancellers and moving target indicators. The invention measures the correlation between a complex main input signal and a complex auxiliary input signal in digital form. It divides the correlation coefficient by the average value of the auxiliary signal magnitude squared, multiplies the ratio by the auxiliary signal and subtracts the result from the main input signal to cancel correlated components.

Abstract: An adaptive N-pulse MTI processor for obtaining optimum clutter cancellation with a minimum of hardware, comprising a first input pulse line; first delay means for providing an interpulse delay T to pulses on this first input line; a first adaptive canceller with its auxiliary input connected directly to take pulses from the first input line, and with its main input connected to take delayed pulses from the first delay means; and N-2 series-connected canceller circuits, with each canceller circuit associated with a different level of pulses. The nth canceller circuit, where 1.ltoreq.n.ltoreq.

Abstract: A method and apparatus exploiting the discovery that the cross-correlation of rows of Frank or P4 matrices of a given spacing sum to zero. In a ranging system, such as a radar, pulses are coded according to the rows of a Frank or P4 matrix, transmitted sequentially and each return processed sequentially through a filter matched to one of the coded pulses. (A different preselected filter is used for each return.) The sequence of filters is chosen so that for returns for a given range interval, each filter is matched to the returning pulse, resulting in outputs from the filters representing auto-correlations of the returned pulses. These outputs are time delayed added coherently to form the compressed pulse, and annunciated as a target hit. Should the filters and returns be mismatched, as with ambiguous stationary clutter returns, the outputs of the filters are cross-correlations which, according to said discovery, sum to zero.