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 pulse expander-compressor for magnifying the range-doppler-coupling effs that accompany the use of frequency-modulation derived phase coded pulse compressors in order to accentuate the doppler-coupling velocity effects on target echoes. The foregoing magnification is accomplished by generating a doppler tolerant polyphase coded waveform with equal time spaces inserted between successive code elements in order to make the time difference between the first and last code elements independent of the number of code elements involved. These equal spaces may be variable in order to allow any desired target radial velocity to produce a phase difference between the first and last code elements of 2.pi..The foregoing may be implemented in a pulse expander-compressor by replacing each delay t.sub.c in the compressor input-signal expansion circuit by a set of N delay elements t.sub.c, and a set of N associated switches, the switches permitting each element in the set to be connected or bypassed, as desired.

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 pulse expansion and compression system, especially useful for radar rang, comprising a pulse coder for expanding an input pulse and a pulse compressor of the matched-filter type. The coder consists of a plurality of delay stages into which the input pulse is fed, a discrete Fourier transform (DFT) circuit to which the output signals of the delay stages are fed by way of respective phase weights and for which every other frequency port is inverted prior to entry to a time-dispersion-means (TDM) comprising an arrangement of adders interconnected by delay stages for differently delaying the output signals from the DFT. The TDM output is fed to a phase modulator and then to the transmitter.The echo signals are conjugated, time-inverted, and passed through the same DFT as the input pulse signal by way of the phase weights. The outputs of the DFT are then inverted at every other frequency port and passed through the TDM, but this time in time-inverted order.

Abstract: A system for polyphase encoding transmitted pulses of energy and for decog the received signals to enhance returns from the range interval being examined during a particular processing period and attenuate returns from contiguous range intervals (pulse compression). The system includes a decoding device which comprises a delay circuit having N distributed outputs including its input for producing a uniform delay between adjacent outputs corresponding to N inputted elements of a received phase-coded signal of length N.sup.2 ; a conjugator circuit coupled to the first N/2 successive outputs of the delay circuit; a first signal-combining circuit coupled to the conjugator circuit and to the last N/2 successive outputs of the delay circuit; a multiplier circuit coupled to the first signal-combining circuit; and a second signal-combining circuit coupled to the multiplier circuit. The decoding device provides a decoding phase shift -.DELTA..phi..sub.k,p to the signal elements of the phase-coded signal wherein.DELTA.

Abstract: A pulse expansion and compression system, especially useful for radar rang, comprising a pulse coder for expanding an input pulse and a pulse compressor of the matched-filter type. The coder consists of a plurality of delay stages into which the input pulse is fed, a discrete Fourier transform (DFT) circuit to which the output signals of the delay stages are fed by way of respective phase weights and for which every other frequency port is inverted prior to entry to a time-dispersion-means (TDM) comprising an arrangement of adders interconnected by delay stages for differently delaying the output signals from the DFT. The adders are connected in N/2-fold cyclically permutated order to the frequency ports, where N is the number of frequency ports if that number is even, and N is the number of frequency ports less one if that number is odd. The TDM output is fed to a phase modulator and then to the transmitter.

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: An impulse interference suppression circuit for use in combination with an -pulse Moving Target Indicator system comprising a gate connected to block the output signal from the MTI system when energized, and a circuit for taking the magnitudes of successive echo return signals, subtracting the magnitudes of consecutive echo signals to remove clutter, comparing the consecutive difference signals from such subtractions against each other, and generating and applying a blocking signal to the gate if the difference between the subtraction difference signals is above a given threshold level.

Abstract: An orthogonalizer wherein a series of complex digital numbers is received, each number having correlated (non-orthogonal) real and imaginary parts; a weight is established which is a measure of the correlation; the product is formed of one of the parts of one of the received complex numbers with the weight; and the product is subtracted from the other part of the one received complex number to decorrelate (orthogonalize) the real and imaginary parts thereof.

Abstract: A device for converting a signal voltage into a multi-bit digital word that efines the voltage magnitude and polarity. The input voltage V to be digitized is used to control the frequency of a voltage controlled oscillator, whose output is defined to be f=f.sub.o +kV. The signal out of the voltage controlled oscillator is fed to differential delay line filters that permit all digits to be derived in parallel. The filters comprise pairs of delay lines of unequal length, each pair feeding a respective phase detector whose output is amplified, and diode-rectified and limited. To increase the accuracy of this device, an automatic frequency control loop can be incorporated to control f.sub.o. This loop zeros V occasionally and reads the output digital word to measure the frequency error and add a correcting voltage to the input voltage V when it is not zeroed for the measurement.

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 canceler for decorrelating one set of signal samples called the main set rom another set called the auxiliary set taken from the same domain. It frequency-translates the signals on their intermediate frequency (i.f.) carrier down close to DC using a local oscillator outside one band edge of the signal and samples the resultant signal at a rate equal to twice the information bandwidth or greater and permits using real rather than complex samples. These samples are then converted to digital information in analog-to-digital converters and are processed digitally at a clock rate equal to twice the information bandwidth or greater. The main signal is processed as above but the auxiliary signal is translated down using the same local oscillator signal and, with the same local oscillator signal phase shifted 90.degree. to obtain an inphase and quadrature signal on the same carrier frequency prior to analog-to-digital conversion.

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 pulse compression system based on the transmission of a step approximat to linear FM pulse, and the subsequent processing of echos therefrom by converting the echo pulses to I and Q baseband signals and then sampling these I and Q signals at the Nyquist sampling rate. It has been discovered that this processing yields a signal with a spectrum substantially identical to the spectrum of a properly sampled Frank coded pulse. These sampled I and Q signals are then compressed by a Fast Fourier Transform compressor to yield a pulse with low sidelobes.

Abstract: A digital pulse expander-compressor for use in pulse compression radars and having the advantage of precompression bandwidth tolerance. The pulse expander-compressor exploys 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 formula ##EQU1## where n is the sequence number of the clock pulse; N is 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 s(k), O.ltoreq.k.ltoreq.N/2-1, by ##EQU2## clock pulse intervals, while delaying the subpulse s(k), N/2+1.ltoreq.k.ltoreq.N-1, by ##EQU3## clock pulse intervals. The subpulse s(k), k=N/2, is not used.

Abstract: A radar system for cancelling radar clutter with a minimum of equipment comprising an N-point Fast Fourier Transform for dividing the radar's doppler space into N contiguous frequency subbands; a delay line disposed at each frequency output port for the FFT for obtaining a set of M+1 consecutive samples from each subband, with the sampling performed at the radar's pulse repetition rate divided by N; a single M degree-of-freedom adaptive-canceller moving-target indicator; and M+1 commutating switches for consecutively applying different sets of M+1 subband samples to the MTI. This operation permits clutter cancellation in each subband with N different frequency zeros placed in the radar's doppler space for each MTI degree-of-freedom.

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.