Abstract: A radar system that enhances the display of moving targets by using negative scan-to-scan correlation to determine which pixels will be displayed at the brightest level. More specifically, a bit image stores a multi-bit scan-to-scan correlated history for each pixel on a display screen, and when new video data is received on a scan, the bit image memory is modified in accordance therewith. A pixel is enhanced to the brightest level only if a return is received from a spacial location from which returns were not received on previous scans. Thus, a target that moves to a new location is displayed at the brightest level because it doesn't correlate with returns from prior scans.

Abstract: Moving target indication unit provided with a doppler filter bank (1) with n output channels A.sub.i (i=0, 1, 2, . . . , n-1), several threshold circuits (24.i) connected to the output channels, a detection and registration unit (7, 14, 18, 23) provided with means (7, 14, 18) for the determination and registration, per azimuth cell, of a parameter for the amount of clutter in an azimuth cell. The said means are further suitable for determining, based on the output signals of the filter bank (1), k (k.gtoreq.2) parameters per azimuth cell and processing per azimuth cell the combination of k parameters to obtain n threshold values, used to set the n threshold circuits.

Abstract: A system for discriminating between signals received on the mainbeam of an antenna system and signals received on the sidelobe of the antenna system. The system utilizes a main antenna and multiple auxiliary antennas. The signals received on the main antenna are coincident on one or more of the auxiliary antennas. The auxillary antenna signals are multiplexed separated for single channel processing. The main antenna signal is compared with each of the multiplexed auxiliary antenna signals. The result of these comparisons are used to determine whether the signal received on the main antenna was received on a mainbeam or a sidelobe.

Abstract: A doppler determination system uses an amplitude comparison of odd and even MTI functions derived from the same signal returns in an MTI radar system to determine the doppler frequency of a target return. The system determines the ratio of the amplitudes of the return of a single canceller circuit with a delay of 2/PRF and the amplitude of the return of a double canceller with two delays of 1/PRF. The ratio is then employed to estimate the doppler frequency of the return. The respective amplitudes of the two MTI circuits are also processed in a 3-dimensional radar application to provide estimates of the target radar cross-section and elevation angle, and with PRF switching to determine the target unambiguous range rate.

Abstract: A radar system adapted to operate with a selected one of a plurality of pulse repetition intervals to produce a corresponding train of transmitted pulses of radio frequency energy in response to a train of trigger pulses and to receive returns from objects in response thereto, with returns from stationary objects producing signals with the same phase shift relative to the phase of a reference signal. The system includes a switching circuit responsive to a signal representative of the selected one of the pulse repetition intervals, for producing charge controlling signals with time intervals between the charge controlling signals and the trigger pulses being selected in accordance with the selected one of the pulse repetition intervals. A pulse forming network, is provided for storing energy in response to the charge controlling signals and for providing output pulses in response to the trigger pulses.

Abstract: The invention relates to a method for frequency-shifting the modulus of the transfer function of a transversal filter.In a transversal filter having three delay lines Z1, Z2 and Z3 in series and four multipliers M'0 to M'3, the multiplier coefficients K0 to K3 of which are intended to eliminate the signals at frequencies in the vicinity of zero frequency and integral multiples of the repetition frequency Fr of the samples X.sub.i, the method consists in replacing the multiplier coefficients K0 to K3 by coefficients K'0 to K'3 which are deduced from the first by multiplying them by fixed coefficientse.sup.3jr, e.sup.2jr, e.sup.jr and 1 with r=2.pi.Fd/Fr.The invention is applicable in particular to the elimination of certain undesirable echoes from radar signals.

Abstract: The invention resides in the fact that the moving-clutter elimination filter is composed of several transversal filters whose n+1 multiplying coefficients K0, K1, . . . , K.alpha., . . . , Kn are fixed and are derived from the coefficients A0, A1, . . . , A.alpha., . . . , An of the fixed-clutter elimination filter by multiplying the latter by the factors:F.alpha.=e.sup.j2.pi.Fd.times.Tr(n-.alpha.).

Abstract: The extraction of radar targets, in particular airplanes or cruise missiles, from clutter is typically based on the target's velocity relative to the ground. Equipment using this principle is usually referred to as a doppler processor or moving target indicator. In situations where severe clutter is encountered, as for example where a look-down radar is trying to find low-flying cruise missiles, extraction of the target solely through its velocity relative to the ground is generally unsatisfactory. A similarly situated human observer looking down can recognize a target both from its motion and the characteristic shape of a fuselage with wings. The principle of this "shape recognition" or "pattern recognition" is here applied to radar by utilizing the so-called radar signature of the target.

Abstract: A radar system mounted on a moving vehicle uses a displaced phase center antanna (DPCA) and associated processing for taking the difference between the two signals received by the displaced antennas to provide moving target indication (MTI) by cancellation of the returns from stationary targets. The presence of moving targets is identified by threshold processing within discrete frequency bands. DPCA processing ordinarily results in amplitude nulls or "blind speeds" for targets moving at particular radial velocities. According to the invention, the two signals received by the displaced antennas are summed, weighted and divided into frequency bands which extend through the expected null region in a form of Doppler processing. Threshold processing is performed on DPCA processed signals within certain frequency bands outside of the null regions and on Doppler processed signals within other frequency bands, thereby substantially eliminating the blind speeds.

Abstract: A moving target indication (MTI) radar which includes TACCAR circuitry or similar means for shifting the frequency of the transmitter/local oscillator, includes a main directional antenna, and subordinate antenna elements for detecting returns from sidelobe directions. The signals from the subordinate antenna elements are modulated, and modulated return pulses are identified and employed to eliminate false pseudo moving target signals which would otherwise be received from the side lobes of the main antenna.

Abstract: A processor adapted for use in conjunction with a monopulse radar system for discriminating between ground and airborne moving targets and comprising: Doppler filter circuits for detecting moving targets; angle measurement circuits which respond to the received sum and elevation difference signals so as to provide an indication of the relative angle of each moving target and of the ground; and means for identifying a detected target as a ground or an airborne target as a function of whether the angle of the target is substantially the same as or different from that of the ground.

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 surface acoustic wave (SAW) radar doppler shift detection system is provided by transmitting a modulation signal having an up-chirp component followed by a downchirp component from a dispersive array SAW assembly to a target, and then receiving the radar return from the target by a receiver which also employs a similar dispersive array assembly. Dispersive array assemblies are constructed with two in line dispersive arrays. The dispersive arrays of the transmitter is positioned relative to two input SAW transducers and two output SAW transducers such that a pulse signal supplied to the two input transducers results in an expanded signal of the output transducers. The expanded signal acts as a modulation signal which is multiplied by an RF and transmitted. The receiving array assembly detects the radar return signal, and, after it is multiplied down to the SAW frequency, compresses it.

Abstract: A moving target indicator device comprising a first clutter removing circuit for responding to a radar having a variable transmit repetition time and for removing clutter having a Doppler speed of nearly zero from a radar received signal having stationary clutter and moving clutter. The device further includes a correction circuit to keep the amplitude components and the phase components of the first clutter removing circuit output substantially constant. A second clutter removing circuit removes clutter having a constant amplitude component and phase component from the output of the correction circuit.

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 eliminating fixed echoes in a pulse radar. The device is provided with a demodulator unit where intermediate frequency signals of the radar are demodulated into video-frequency signals. The video-frequency signals are utilized in a utilizing unit provided with a display unit. A processing unit of the video-frequency signals is connected between the demodulator means and the utilizing unit. The processing unit is constituted with a range unit sampling circuit, a Doppler filtering unit and a video-frequency signal dynamic compressing unit connected in series.

Abstract: A circuit for generating an output signal L indicative of the mean clutter level at a selected location in the field of view of a radar apparatus, particularly the sea surface which exhibits a swell pattern. The circuit includes processing circuits which generate weighting coefficients (a.sub.1, a.sub.2, . . . a.sub.N) used to weight the amplitudes of returns derived respectively from a group of N discrete locations which precede in range and or succeed in range the selected location. The circuit generates the elements r(n) of a matrix [r] which represents the auto correlation function of the amplitude of returns derived from w discrete locations encompassing the group of N locations. Circuit then uses the matrix [r] to compute the weighting coefficients (a.sub.1, a.sub.2. . . a.sub.N) which are stored at 13 applied to respective multiplying circuits to weight corresponding amplitudes accessed to respective locations of a shift register.

Abstract: A Radar Digital Data Processor has been developed which produces I (phase) and Q (quadrature) data obtained by sampling the receiver IF of a radar with a single A/D converter. A sampling technique was developed for this application to allow operation with radars employing a noncoherent transmitter such as a magnetron. Representative field results are presented employing spectral analysis proving the viability of the sampling technique for Doppler processing.

Abstract: A radar signal processor and methods of operating same for determining the differential sideband power of reflected energy received in a frequency window by a radar receiver, which processor contains a generator of orthogonal signals, a mixer for multiplying these orthogonal signals times quadrature signals, an integrating circuit for integrating the mixer outputs over a predetermined time interval, a multiplier for multiplying the integrals from the integrating circuit together, and a circuit to average the products from the multiplier over time.

Abstract: Apparatus is provided for the automatic in-line measurement of background noise for MTI radar with automatic suppression of samples not originating from noise. The background noise level is determined by making use of summing and shifting operations only, and the suppression of samples not originating from noise is obtained by utilizing the information derived from a normal radar detector so that samples identified as true targets shall not contribute to the calculation of background noise level.The apparatus comprises a multiplexer circuit (22), a first shifting circuit (23), a storage element (24), a second shifting circuit (25), an inverter (21), and a counter (26).

Abstract: A pulse doppler radar having variable repetition rates, noise pulses resulting from echos received from stationary multiple-time-around objects are removed by subjecting the reflected pulses to a coherent integration modified by means of a simplified vectorial addition of the reflected pulses, using an integration circuit consisting of a plurality of filters.The signal amplitude produced at the output of each filter is individually compared to the mean value of signals produced by all other filters, and a target indication is produced when the mean value is exceeded by the amplitude of a signal from an individual filter.

Abstract: An adaptive detection threshold system for moving target detector and moving target indicator radar systems. The threshold system uses data from the echo input signal to reconstruct a threshold level closely resembling the output clutter residue in doppler filters due to point clutter sources. At least three azimuth data values are used, with the values being from adjacent coherent processing intervals and separated in azimuth a distance approximately equal to the beamwidth of the antenna system. The data at the same range from the three azimuths is combined to form an estimate of the residue at the output of a doppler filter, assuming that the echo is caused by point clutter. Compensation for radar instability and changes in scan rate or interpulse period is included. Data from conventional constant false alarm rate processing designed to control alarms from distributed interference, such as weather echoes, is also used to compensate the residue estimate.

Abstract: A multiple range interval clutter cancellation circuit for MTI radars is disclosed, for assuring cancellation of narrow band clutter in the second or further range interval, while preserving wideband cancellation in the nearer range intervals and economizing on the number of fill pulses. The circuit includes two clutter cancellers. One canceller has a relatively narrow band clutter rejection bandwidth, and effectively a higher number of fill pulses in relation to the clutter rejection bandwidth and effective number of fill pulses for the second canceller. The outputs of the two cancellers are subjected to an AND gate function, such that only targets which pass through the clutter rejection bandwidth of both cancellers are reported as a target. The circuit obtains the elimination of returns from ambiguous range interval clutter with less transmitted energy and time than conventional canceller circuits.

Abstract: A radar target simulator apparatus and method especially useful with a pulse compression radar located in a remote, unattended, and unpowered, terrain. Provision for generating signals which will pass through moving target indication (MTI) and minimum velocity threshold circuits are included. Transmission of the detected simulated target data through narrow-band communications lines, such as telephone lines, is contemplated. The capability for minimum discernible signal and radar power output evaluations are also provided.

Abstract: Clutter suppressors and methods of clutter suppression for radars which employ the doppler effect for enhancing signals due to moving targets relative to signals due to clutter caused by land, sea or rain. Specifically, the disclosure concerns suppressors and methods of clutter suppression for cw doppler, pulse doppler and MTI (moving target indication) radars. The suppressors reduce the occurrence of radar output due to clutter by permitting and prohibiting radar output on the basis of the strength of signals that contain doppler frequency components of the radar echo.

Abstract: A surface acoustic wave (SAW) device in a pseudo-coherent moving target indicator uses a common input transducer to delay both reference and signal inputs to a mixer by varying amounts. The mixer produces a Doppler signal which is processed within a single range cell. The SAW device may contain additional delay paths which drive other range cells. Power splitting and amplification sections of the moving target indicator are minimized through use of the SAW device.

Abstract: A flat plate reflector at one station, responsive to ambient vibrations, is illuminated by a narrow beam of radio frequency waves transmitted from a second location, the transmitted waves being modulated in direct proportion to the ambient vibrations and reflected back to the second station for analysis.

Abstract: An adaptive radar signal processing apparatus for a radar system wherein filter coefficients are switched for individual regions so that optimum filter characteristics can be obtained for the individual stationary clutter region, moving clutter region, clear region, etc. thereby providing suppression of undesired signals which is adapted for each region.

Abstract: A radar system comprises means for forming a transmission pulse signal as m sets of n pulses, the individual sets having respective PRPs Ti (i=1, 2, . . . , m) moving target detection means, and angle measurement means utilizing beam-to-beam amplitude comparison and interpolation for a given moving target. Beam-to-beam amplitude comparison and interpolation is carried out at least twice for one target by making use of a pair of video signals with the same PRP processed by the moving target detection means. The angle measurement is achieved through a predetermined correlation processing over thus obtained interpolated angle values for a target.

Abstract: An N-point Fourier transform circuit for a moving target indicator system including a delay circuit with 2N-2 delays, N frequency filters, a processor for forming a main signal and N-1 auxiliary signals via time sample manipulation, a Gram-Schmidt adaptive canceller circuit for decorrelating the N-1 auxiliary signals from the main signal, and a first and second commutating switches. The first switch tracks a given set of N time samples through the delay circuit. The second switch switches the given set of N time samples through a different successive frequency filters of the N frequency filters every transmission. The first switch tracks in synchronism with the second switch and switches to obtain a new given set of N time samples every NT seconds.

Abstract: A coherent-on-receive MTI radar receiver system for use with cooperative or non-cooperative radar transmitters of either the coherent or noncoherent, simple magnatron type and scanning antennas. The receiver includes coherent digital signal processing with provision for normalizing or compensating phase variations in the transmitter carrier pulses.

Abstract: An MTI radar provided with a MTI processor which includes a single erasing circuit for erasing a vector signal due to a stationary target from among all the input vector signal of reflected waves both from a moving and a stationary target; and an arithmetic circuit for removing any other variations than ones from the moving target by calculating the inner product of the post-single-erasing vector signal and a pre-erasing vector signal.

Abstract: A receiving section of a surveillance radar equipped with a power oscillator in its transmitting section comprises several registers for the storage of values, perferably in complex digital form, representing the starting phase of a continuous wave at the instant of transmission of an outgoing pulse, these values being used thereafter to establish coherence with an incoming echo pulse at a time when the power oscillator is no longer able to do so on account of unavoidable frequency drifts or because of intervention of a new recurrence period. Thus, the stored values permit the correct detection of targets at the far end of the range and/or the cancellation of second-time-around clutter echoes. The continuous wave may be generated by a coherent oscillator, phase-locked during each recurrence period by the outgoing pulse, or a separate crystal-controlled oscillator of highly stable frequency.

Abstract: A space-time adaptive filter system is provided for eliminating unwanted signals from a radar or communication system. The filter system receives a main channel and several auxiliary channels wherein the target signal is not correlated between the various signal channels. Correlated noise components are eliminated by decorrelating the signals. The adaptive filter includes a Gram-Schmidt processor for sequentially decorrelating the auxiliary signals from the main signal. Each decorrelation element of the Gram-Schmidt processor comprises a transverse orthonormal ladder filter.