Abstract: The present invention relates to a signal processing method for a radar system. The transmitted signal here includes a polyphase code that is optimized to the desired range/Doppler range and that is repeated periodically over time.

Abstract: Received expanded radar pulses pass through a surface acoustic wave (SAW) weighted filter (64) for sidelobe suppression, and then into a SAW tapped delay line (66). The pulses appear at the taps (66a,66b,66c) of the delay line (66) coarsely aligned in time, pass through individual SAW matched filters (68,84,86,88) for compression and envelope detectors (70,90,92,94) for demodulation, and then into a summer (74) for post detection integration. Individual frequency shifters (78,80,82) are provided between the delay line taps (66a,66b,66c) and the matched filters (84,86,88) for shifting the center frequencies of the pulses and thereby the propagation delays through the matched filters (84,86,88) to provide fine alignment of the pulses in time. The delays through the individual delay line taps (66a,66b,66c) and the frequency shifts of the frequency shifters (78,80,82) are adjustable "on the fly" to compensate for variation of pulse repetition rate (PRF) and interpulse jitter.

Abstract: An impulse radar that forms a predetermined radar pulse train in space by transmitting individual spectral components thereof. Thus, a train of extremely short pulses is obtained without switching a radio frequency signal on and off at a high rate. An oscillator is coupled to a harmonic generator, and a power divider distributes the output of the harmonic generator to a multiplicity of amplifiers. Each amplifier has a phase-locked VCO circuit that provides frequency accuracy, spectral purity, low noise and frequency stability. Thus, each amplifier provides one of the spectral components of the predetermined radar pulse train. The amplifiers are coupled to a multiplexing feed that illuminates a reflector. On receive, the multiplexing feed separates the spectral components of the incoming pulse train. Each spectral component is coupled to its own narrow band receiver, and one receiver is used to amplify and detect each spectral component.

Abstract: A digital pulse compression apparatus comprises a plurality of doppler correction circuits for carrying out doppler correction in the time domain or the frequency domain and for carrying out pulse compression, and a maximum amplitude selecting means for selecting and outputting the maximum amplitude signal out of the compressed signals obtained from the doppler correction circuit at the rate of range bin period. The present invention can supply a pulse compression apparatus having a stable compression performance, even if a doppler frequency of the input signal is not known.

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: An apparatus and a method for enhancing the radar cross section of a target. The present invention is an impulse radar system that implements a method that comprises the following steps. A pilot impulse radar pulse is transmitted at a target. The pilot pulse comprises a plurality of individual pulses having respective distinct frequencies generated by the impulse radar system. A return pulse from the target is received by the impulse radar system and provides information indicative of target scattering centers. The return pulse is used as a calibration signal for generating a phase conjugated pulse. The phase conjugated pulse is then transmitted at the target. Processing a target return signal derived from the transmitted phase conjugated pulse enhances the radar cross section of the target because the waveform of the transmitted phase conjugated pulse is matched to the characteristics of the target.

Abstract: The present invention is a system that performs code compression in stages where each stage includes two processing paths 36 and 38. The two paths allow bidirectional crossover cascade complementary code compression reducing the number processing stages to log.sub.2 N and reducing the number of processing by a factor of N/(2 log.sub.2 N) where N is the length of the code. Each path includes a delay provided by a delay unit 44 and each path arithmetically combines the data from its own path with data from the other path. The upper path 36 uses an adder 40 while the lower path uses an adder/substracter unit 42 which adds or subtracts depending on the phase of the transmitted complementary phase code. The delay provided in each stage increases in a binary progression with the delay of the last stage being N/2. A systolic processor 68 is the preferred embodiment although the invention could be implemented in a programmable digital signal processor.

Abstract: A predetermined radar pulse train is formed in space by transmitting individual spectral components thereof. Thus, a train of extremely short pulses is obtained without switching a radio frequency signal on and off at a high rate. A crystal oscillator is coupled to a harmonic generator such as a comb generator. A power divider distributes the output of the harmonic generator to a multiplicity of final filter amplifiers. Each final filter amplifier has a phase-locked VCO circuit that provides frequency accuracy, spectral purity, low noise and frequency stability. Thus, each final filter amplifier provides one of the spectral components of the predetermined radar pulse train. The final filter amplifiers are coupled by duplexers to a broadband multiplexing feed such as a nested cup dipole feed that illuminates a reflector. On receive, the broadband multiplexing feed separates all the spectral components of the incoming pulse train.

Abstract: A radar system is disclosed which includes a transmitter which produces a long coded radar pulse. The return of the long coded radar pulse is compressed by a long pulse compression filter to produce a short coded pulse and the short coded pulse is compressed by a short pulse compression filter to produce a return pulse for processing by an existing processor designed to process return coded pulses of a particular format. The long pulse transmitter can also transmit a short coded precursor pulse, to improve radar range coverage, along with the long coded pulse by the provision of a switching bypass device which routes the short coded pulse return signal around the long pulse compression filter.

Abstract: Unique stretch and chirp waveform formats are described which allow significant simplification of radar signal generation and receive processing hardware. The new formats produce a non-zero intermediate frequency (IF) to facilitate in-phase and quadrature (I/Q) processing but allows the use of a homodyne type of receiver architecture. That architecture greatly simplifies the receiver hardware because the first local oscillator (LO) signal is simply a sample of the transmitter drive signal and no second LO is required. The non-zero IF is achieved by control of the timing and start frequency of the first LO waveform for stretch processing and timing of the transmit signal gating for chirp processing.

Abstract: A multi-pulse pulse compression radar system transmits two or more radar pulses having different frequency components having a time delay therebetween. A signal conditioning stage time and phase aligns the received signals and provides a composite radar signal having time and phase continuity throughout.

Abstract: A radar ranging system is disclosed which employs a frequency modulated and phase coded transmission signal which can have up to a 100 percent duty cycle and which performs time tracking of the radar target and does not require extreme accuracy in frequency modulation, or extreme receiving antenna to transmit antenna isolation.

Abstract: A radar transmitter chain employing injection locked oscillator, e.g., a magnetron, as an output stage. Problems arise with maintaining the injection locking bandwidth centered on the radar source transmit frequency. This alignment is maintained by allowing the magnetron (38) free running frequency to drift, along with its injection locking bandwidth and then to force the radar source frequency (30) to follow the magnetron frequency. A phase difference measurement (44) between the injection signal (35) and the magnetron output signal (37) provides the control for a feedback loop (60) which may control a tunable VCO (48) or selection from a bank of fixed frequency oscillators (78).

Abstract: A radar system, such as a tracking radar installation or other radar installation which is of the pulse compression type, transmits data during transmission of the radar signal. The data is transmitted by inserting, into the radar signal, at least one short nonpulse interval. The position of the nonpulse interval within the radar pulse can be modulated.

Abstract: An optimization method for sidelobe suppression filters, and a filter utilizing a binary coding waveform are formulated. The method comprises expanding the frequency transfer function of an ideal sidelobe suppression filter into a polynomial series; truncating the polynomial series into a finite-termed polynomial series with unknown weighting coefficients A,B,C,D . . . , using the inverse Fourier transform to convert the finite-termed polynomial series into the corresponding pulse response in the time domain; then using the LP algorithm to minimize the output peak sidelobes to determine all the weighting coefficients A, B, C, D . . . and inserting them back to the inverse transfer function of the optimized filter.

Abstract: A short-range radar system having a unquie method of processing a linear CW signal so as to provide target range information at the time of target detection. The linear FW/CW signal is mixed with a portion of the transmitted signal and with an intermediate frequency ramp signal to produce a difference frequency signal in the form of a frequency ramp which is a function of the range to the target. The ramp signal is then converted to a pulse which is determinative of the range to the target.

Abstract: A synthetic aperture radar system wherein a plurality of beams is formed for receiving echo signals and the spectra of the received signals are synthesized in an azimuth compression unit to improve the cross-range resolution.

Abstract: A waveform generator (12') is responsive to a reference clock signal input for producing an output waveform which is a linear FM waveform. A reference clock signal is supplied to the generator which performs a double integration to obtain the phase of the output signal. The phase resulting from the double integration is used to obtain the sine of the phase using a lookup table. The sine of the phase is input to digital-to-analogue (D/A) converter, and the output from the D/A converter is filtered using a bandwidth matched to the bandwidth of the transmitted signal. The generator is useful in radar systems for area mapping and target identification.

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 pulse compressing apparatus for use in a radar system receives an input signal data stream which has been received by the radar system and which corresponds to a transmitted long pulse. A weight coefficient generator generates the same number of weight coefficients as the number of input signal values in the input signal data stream. The same number of arithmetic units is provided and the weight coefficients are sequentially transferred to each arithmetic means where they are processed with the input signal values. The results of the processing from the arithmetic units are added together to produce a compressed pulse output.

Abstract: An improved radar receiver transmitter uses a single oscillator frequency shift keyed system in which the oscillator shifts rapidly between a pulsed output frequency and a local frequency such that the system can transmit at one frequency and shift fast enough such that when the echo pulse is received, the transmitter is operating at the local frequency desired. The two signals are demodulated in a mixer to establish the desired intermediate frequency which then may be processed to produce the desired output. Extremely fast shifting is accomplished by a gallium arsenide oscillator in conjunction with a varactor diode which responds to a modulator pulse.

Abstract: A coherently interruptible frequency hopped chirp waveform generator has a ignal generating synthesizer and a chirp generator with digitally stored chirp samples in which both are phase locked to a reference clock and responsive to a timing and control circuit. The digitally stored chirp signal sample is D/A converted and mixed with a fixed frequency signal generated by the synthesizer forming translated chirp signals. The translated chirp signals are output, being controlled by a timing and control circuit so that a plurality of coherently interruptible and frequency selectable chirp sub-pulses are formed.

Abstract: A method and a device which make it possible, simultaneously and in a perfectly identical manner, to process n analog signals (E.sub.1, E.sub.2 . . . ) of short duration. The device comprises n processing channels (V.sub.1, V.sub.2, . . . ) each receiving an analog signal and each possessing in series, a processing circuit (11, 12; 21, 22; . . . ) for frequency transfer (F.sub.1, F.sub.2, . . . ), and a delay circuit .tau..sub.1, .tau..sub.2, . . . (13, 23, . . . ) respectively. A set of switches (C.sub.1, C.sub.2, . . . , C'.sub.1, C'.sub.2, . . . ) interconnect the inputs and outputs of the various elementary processing channels (V.sub.1, V.sub.2, . . . ) in order to pass each signal through all the n elementary channels (V.sub.1, V.sub.2, . . . ) successively and sequentially, for a processing cycle. This permits the fine analysis of the echo signals received from a target consisting of several bright points, by a pulse compression radar.

Abstract: A transmitting channel includes a pulse generator unit for generating frequency or phase code modulated pulses having a common centre frequency. The pulses are transformed to a transmitting frequency in the transmitting channel. An antenna, which is connected to the output of the transmitting channel, radiates the transformed frequency pulses and receives return signals. A receiver channel processes the return signals. The receiver channel includes a pulse compressor unit for compressing the return signals. Each pulse to be transmitted consists of two or more sub pulses, at least one of the sub pulses being substantially longer than at least another one of the sub pulses. Each sub pulse is coded with a different compression code. The compression code of each sub pulse having a low cross-correlation property with the compression codes of all other sub pulses, all sub pulses having the same center frequency.

Abstract: In a radar system, comprising a digital expander, two analog modulation signals are generated with two digital to analog converters and raised to an intermediate frequency range through a quadrature modulator. The amplitude and phase ripple of the output signal occurring in the quadrature modulator due to limited carrier and image frequency suppression are compensated through a multiple regulating circuit. To this end, if necessary calibration signals, of constant amplitude and different phase positions, are generated sequentially by means of the two digital to analog converters and the amplitude of their output signals measured in an amplitude detector. Setting values for the multiple regulating circuit are determined from the averaged amplitude measured values in a phase and amplitude correction unit which via setting elements set the requisite offset and phase and amplitude symmetry values until the deviations of the output signal in amplitude and phase disappear.

Abstract: The invention relates to a coherent radar comprising a magnetron (MAG), a modulator (MOD) for pulsing the magnetron, a stable local oscillator (STALO) and a mixer (B.sub.1) for producing an intermediate frequency signal of incoming echoes and an intermediate frequency oscillator (MFO) and a phase sensitive detector (D) for detecting the echo pulses and producing a so called bipolar video signal. The modulator (MOD) and the intermediate frequency oscillator (MFO) are mutually time controlled in such manner that the front flank of the modulator pulse and thereby the magnetron pulse always appears in a predetermined phase position of the output signal of the intermediate frequency oscillator. According to the invention the oscillations of the magnetron are phase locked to an external signal in two steps. This is effected by applying a signal derived from the stable local oscillator to the tuning cavities of the magnetron before triggering.

Abstract: A pulse radar system including an RF exciter for generating a repeating sequence of internal pulses of RF energy of different frequencies. A transmit circuit responsive to the internal pulses of RF energy generates a transmit radar signal comprising a transmit repeating sequence of transmit intervals during which pulses of RF energy are transmitted. A single receiver responsive to the repeating sequence of internal RF pulses receives radar return signals based on all of the RF frequencies in a receive repeating sequence of receive intervals which do not occur at the same time as said transmit intervals.

Abstract: A swept-frequency radar system transmits pulses consisting of swept-frequency subpulses of nonuniform duration separated by short nontransmitting periods during which an array antenna is resteered. The pulses reflected from a target are processed by a method including estimating the target ranges, producing a reference signal at the time at which the pulse reflected from the target is expected to return. The reflected pulse is phase detected by means of the reference pulse to produce phase detected signals which include information relating to the error between the actual range and the estimated range. The phase detected signals are Fourier transformed to produce range error information. The nonuniform subpulse durations reduce the magnitude of range sidelobes.

Abstract: A Doppler matched binary pulse compressor having means to initiate operation, means to generate a Doppler matched filter bank, means to compress the pulses from the Doppler matched filter, either linear or soft limited, means to estimate the signal phase in real time and means to select overall optimal filters in real time. The foregoing includes a phase estimator having a quadrant detector and means to scale the quadrature components while preserving the signal phase, means to reduce accuracy computations to 45.degree. or less of the first quadrant, and means to reconstruct the phase to place the signal in the proper quadrant.

Abstract: The invention relates to a method for radar mapping an area and a radar equipment for wideband exploration at frequencies below 300 MHz. A large number of frequencies, for instance 1000, are distributed over a frequency band between for instance 12.5 and 200 MHz, and approximately corresponding to terms in a geometrical series but being different harmonics to a certain fundamental frequency. This is accomplished by a synthesis generator (1) coupled to a phase control device (7) and the generated frequencies are each amplified in a separate amplifier (2), the outputs of which are guided in groups to a number of antennas, tuned to different frequency bands and fewer than the number of frequencies. The reception is carried out in a similar way from the antennas with pre-amplifiers and a mixer (3) each and an A/D-converter (4) and a registration device (5). The equipment is meant to use the principle of so called synthetic aperture (SAR).

Abstract: The surface acoustic wave device which generates two coherent signals from a single input. The inventive device has three interdigital transducers (IDT) spaced upon a single piezoelectric substrate. The central IDT has three sets of interdigital fingers.A power splitter and an amplifier are connected between the central IDT and one of the other IDT's to form a recirculation loop. An input signal burst applied to the central IDT produces two coherent outputs at the remaining IDT and the power splitter.

Abstract: Pulse-compression method employing space-coding, according to which a plurality of pulsed signals are emitted, simultaneously, for a time (1/.DELTA.f), at frequencies which are uniformly graded by an increment (.DELTA.f), the pulsed signals which are returned by any target being spatially compressed, the compression factor being equal to the number of signals which were emitted simultaneously.

Abstract: An interrogation-answering system is employed in conjunction with a primary radar wherein a single joint transmitter is utilized both for generating the interrogation signals and the simple primary radar signals.

Abstract: A radar transmission, reception and signal processing system generates high esolution synthetic aperture radar ground maps from air or space platforms using waveforms in which frequency is changed pulse-to-pulse. The transmitted radar signal is comprised of a series N bursts with n pulses per burst wherein each of the pulses is a fixed frequency step, .DELTA.f, either above or below one or the other of the n pulses, i.e. the n pulses comprises an ordered set and further, preferably, wherein the set of n pulses is arranged in time as a random permutation of the ordered set. In each of the k sample gates for each burst the n complex samples of reflectivity are inverse Fourier transformed from frequency domain samples of reflectivity to synthetic range domain profiles to result in an array of aligned range profiles in each of k coarse range delay positions.

Abstract: The present invention includes an apparatus that prebiases a transmitted radar signal. The prebiasing of the transmit signal automatically aligns the return signals in one dimension or dimensionally transforms the return signals thereby removing the need for one of the dimensional processing operations of a conventinal two dimensional return signal interpolator. A map function generator produces small frequency (phase) changes in the transmitted signal during each pulse over the entire integration or exposure period. The map function generator produces a parabolic frequency change control signal applied during the integration period. The control signal is divided into segments where each segment controls a single transmit pulse. The control signal modifies a linear frequency modulation control signal. conventionally produced by high resolution radar systems.

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 method of preventing interference between `friendly` pulse doppler radars when in action against a common target or adjacents targets. Despite considerable separation of the radar r.f's the pulsed signals have repeated sideband pulses which may be taken by another radar as a doppler-shifted echo. This problem is to a large extent alleviated by frequency modulating the r.f. transmission at a very low cycle rate of the order of one cycle per second and at a modulation rate sufficient to indicate to a receiving radar that the source could not be a target accelerating at such a high rate.

Abstract: A solid state radar transmitter pulse modulator system capable of generating high power operating pulses having pulse width and pulse repetition rate agility and being programmable for output pulse current over a substantial range of peak current values to produce corresponding values of transmitter output power. A multi-stage cascade cross-field amplifier (CFA RF chain) is employed, each stage having its own pulse modulator comprised of one or more standard modules paralleled at the output to drive the corresponding CFA stage provides fail-soft operation. Means are included for protecting solid state circuits in the event of CFA or other component failures, for dynamically matching CFA and pulse transformer impedances, and for preventing BH curve "walk-up" during operation.

Abstract: The invention comprises a weather radar system in which a magnetron transmitter is controlled in frequency by injecting therein a low power locking signal from a stable frequency source. Frequency lock between the source and the magnetron is maintained without requiring injection signals of excessive power by an automatic frequency control (AFC). The AFC determines the frequency and phase error between the injection signal and the magnetron output and adjusts the frequency of the source so as always to be within a narrow band of frequencies centered about the natural frequency of the magnetron. Over the long term, therefore, the frequency of the source will vary by an amount equal to the change in the natural frequency of the magnetron occurring during that time. Over the short term, however, the difference in frequency between the injection signal and the magnetron output is zero, while the phase difference is less than 90.degree..

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 multi-arm frequency sweep generator 10 provides frequency sweep characterized by precise waveform control (linearization), steep slopes, and a high repetition rate. An impulser (12) generates pulses which are distributed by a multiplexer (14) to the multi-arms of the frequency sweep generator. Each arm includes a reflective array compressor (RAC) 16 for dispersion a throughgoing pulse into a frequency sweep of low enough slope that it can be effective corrected by means of complex multiplying digital-to-analog converters (18). The corrected sweeps are summed by a demultiplexer (20). A compressor RAC (22) compresses the summed output to provide sweeps with slopes steeper than would normally be correctable by the MDACs.

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.

Abstract: Frequency domain, pulse compression CW radar apparatus comprises a frequency synthesizer which provides RF and IF CW signals and linear frequency modulator (LFM) which provides a saw tooth LFM ramp signal with the f.sub.LFM. A mixer combines the f.sub.LFM signal with the f.sub.RF signal to provide a CW radar signal having a frequency, (f.sub.RF +f.sub.LFM) for transmitting by a transmitter. A receiver receives time-delayed CW radar return signals reflected, for example, from clutter at a one range and from a target at another range. A second mixer down-converts the clutter and target return signals to an intermediate frequency for processing and a third mixer extracts the f.sub.LFM signal from the intermediate frequency clutter and target return signals to provide, in a frequency-time domain, rectangular wave, clutter and target signals.

Abstract: A system for generating a sequence of pulses of carrier having individually selectable frequencies employs a pulsed oscillator for providing a single pulse of a carrier signal having a predetermined frequency. The single pulse is applied to a dispersive filter imparting a delay to signals dependent of their spectral content. The relatively broad spectrum of the single pulse is converted by the dispersive filter into a swept frequency pulse of much longer duration than the input pulse to the filter. The expanded signal is mixed with a set of mixing frequencies to provide a set of expanded signals, each of which is then gated to attain spectral portions having desired average values of frequency. The expanded signals are then summed together and applied to a compressive filter which operates in the mirror-image format to the dispersive filter.

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 device for determining the frequency range and chirp rate of chirp radars or other sources of frequency-modulated signals includes a compressive receiver (16, 22, 24) for time-compressing single-frequency signals and a discriminator (26) for generating an output that represents the instantaneous frequency of the compressive-receiver output. For narrow-band signals, the frequency-modulated components in the output of the compressive receiver do not last long enough to cause a response from the discriminator (26). When the input of the compressive receiver is a chirp signal, on the other hand, the resultant compressive-receiver output lasts long enough to cause a discriminator response, and its time of occurrence and rate of frequency change are indications of the frequency range and chirp rate of the compressive-receiver input. The discriminator (26) accordingly generates an output whose slope is an indication of the chirp rate of the compressive-receiver input.

Abstract: In a radar system comprising equipment for transmitting frequency modulated pulses and compressing the received signals in a filter for frequency-dependent weighting, the weighting is asymmetrical in a manner such that the leading sidelobes of the pulse compression signal are reduced and the lagging sidelobes are raised. The reduced leading sidelobes can easily be reduced below an amplitude threshold so that the main echo lobe within the pulse compression signal is reliably acquired for determining the closest target distance. The invention may advantageously be applied to ground tracking radars.

Abstract: A decoding device for use in pulse compression radars to decode a novel pe code that has the advantage of precompression bandwidth tolerance. The novel code type is described by the following formula (where .DELTA..phi..sub.k,p is the phase change at the kth subpulse of the pth subsequence within the width of a phase-modulated pulse):.DELTA..phi..sub.k,p =(2.pi./N) [k+pN][p-(1/2)(N-1)]k=0, 1,2, . . . , N-1p=0, 1,2, . . . , N-1 (N any integer)The input signal is fed into multi-stage I and Q shift registers. Each stage in the shift register is fed into an adder, correlation being effected by first multiplying the real and quadrature parts of the signal stored in the stages of the I and Q shift register by a preselected multiplying factor, the sequence of multiplying factors corresponding to the time-reversed and negative phases of the transmitted pulse. The sum signal at the output of the adder corresponds to the auto-correlation function of the received signal.

Abstract: This concept makes use of the orthogonal nature of Group-Complementary Co to achieve improved polarization isolation between the vertical and horizontal radiation in a circularly polarized or dual linearly polarized antenna system while achieving zero time-sidelobe responses in pulse compression. Two channels of a radar system are established with each being encoded using an orthogonal Group-Complementary Code. One channel is associated with the vertical polarization of radiation while the second is devoted to the horizontal polarization. With a leading or lagging 90 degree phase relationship between the two channels, right hand or left hand circular polarization can be established according to the code of each channel which controls the relative phase. Such a technique of pulse compression and group complementary coding offers improved polarization isolation between channels while achieving zero-time sidelobes in pulse compression.

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.