Abstract: A radar system and technique provide the capability to detect a target of interest and maintain the detection in the presence of multiple mainlobe and sidelobe jamming interference. The system and technique utilize the versatility of digital beamforming to form sub-arrays for canceling jamming interference. Jamming is adaptively suppressed in the sub-arrays prior to using conventional deterministic methods to form the sum, &Sgr;, and difference, &Dgr;, beams for monopulse processing. The system and technique provide the ability to detect a target of interest, provide an undistorted monopulse ratio, m, and maintain target angle estimation, in the presence of multiple mainlobe and multiple sidelobe jammers. Further, this system and technique are not constrained by requiring a priori knowledge of the jamming interference.

Abstract: A method and system for identifying the locations of plural targets lying within a main beam of a monopulse antenna including four ports for generating sum, elevation difference, azimuth difference and double difference signals. The method comprises the steps of forming a monopulse ratio matrix from the sum, elevation difference, azimuth difference and double difference signals; and determining eigenvalues of the monopulse ratio matrix. These eigenvalues are then used to determine the angular locations of the plural targets. Preferably, the eigenvalues are determined by performing an eigenvalue decomposition of the monopulse ratio matrix to generate eigenvalues, and the angles of the targets may be determined from the eigenvalues by the use of a look-up table.

Abstract: A radar system includes a null processor coupled to transmit receive modules. The null processor inserts nulls in the sum pattern at locations for suppressing a jamming source. The null processor determines the difference pattern based upon the product: sum*sin(x), where sum is the sum pattern and x is the azimuth angle.

Abstract: A system for monitoring of the position of at least one portion of an object. The system includes a plurality of transmitters operative to transmit alternating magnetic fields within a three-dimensional space, and at least one positioning sensor arranged to be fixed to at least one corresponding portion of the object whose position it is sought to monitor. Each of the positioning sensors includes a magnetic field receiver having at least one active axis and operative to receive at least one component, lying along the at least one active axes respectively, of the alternating magnetic fields.

Abstract: A monopulse antenna system comprising an inner antenna and an outer antenna disposed symmetrically about a central axis of symmetry. A central aperture is located at the axis of symmetry through which a weapon system may fire or an additional sensor may be located. The inner antenna is preferably annular in shape and produces a relatively broad antenna pattern. The outer antenna is also preferably annular and produces a beam pattern with many lobes. The received signals A and B, from each beam pattern, are combined in a hybrid to produce sum signals (A+B) and difference signals (A−B), which are then processed to produce a target off-axis radius relative to the antenna main beam axis, i.e., the axis of symmetry.

Abstract: A signal process is provided for radar interference mitigation in SAR data and to perform several functions. Initially, the algorithm separately removes the average range bias of the I-channel and the Q-channel data. Next, I- and Q-channels are equalized by properly compensating their phase difference and gain imbalance due to either constant or random timing jitters. The current implementation well compensates relative I/Q timing jitters within two sampling time intervals which, for the FOPEN III receiver, are 4 nanoseconds. Graceful performance degradation of the algorithm is expected when timing jitter exceeds two sampling intervals. For example, phase jitter on the order of 5 sampling intervals will be partially but not perfectly corrected. Following the I/Q equalization, adaptive RFI rejection is performed. The FOPEN III data bandwidth may also be reduced 50% with hardly any information loss.

Abstract: The process is used for suppressing the effect of signals that are received or sent via side lobes of an antenna (PA; HA) of an amplitude or phase monopulse radar device, in which for the purpose of position measurement of a first and, if need be, a second target (T1, T2) detected by the radar beam, three illumination functions Je(Lx), Jk(Lx) and Js(Lx) for the antenna (PA; HA) are provided for each measurement axis, as well as antenna functions Fe(X), Fk(X), and Fs(X) resulting from them. The first, second, and third illumination functions Je(Lx); Jk(Lx), and Js(Lx) are selected in this connection so that a quotient function Qe(X)=Fe(X)/Fs(X) or Qk(X)=Fk(X)/Fs(X), which is linearly or quadratically dependent on the target direction, is produced by normalizing the first and the second antenna functions Fe(X); Fk(X) with the third antenna function Fs(X). The power of this quotient is compared with at least one threshold value th.sub.e or th.sub.

Abstract: A wireless base station equipment includes a transmission power controlling unit for controlling a transmission power of a transmitted signal to be transmitted to a mobile station in accordance with a status of signal reception from the mobile station and a beam tilt angle varying unit for varying a beam tilt angle of an antenna formed with respect to a horizontal plane, based on the level of transmission power control by said transmission power controlling unit.

Abstract: A space vehicle uses a signal received from a global positioning system (GPS) satellite (51, FIG. 1) to determine the attitude of a space vehicle. The signal is received through a pair of antennas (10, 11) and converted to sum and difference outputs by a sum and difference circuit (30). These outputs are then conveyed to down converter/correlators (55), and then to envelope detectors (60). The outputs of the envelope detectors (60) are then converted to a digital format by an analog to digital converter (70). The digitally formatted sum and difference amplitudes are then used by a processor (80) to calculate the required attitude adjustment to the space vehicle.

Abstract: An inertial navigation system (INS) and a monopulse radar system are mounted on a body. The inertial navigation system outputs at least a velocity of the body. Either a synthetic aperture radar (SAR) map or doppler beam sharpening (DBS) map is created using the outputs of the monopulse radar system. The monopulse radar system outputs at least a summation output, an azimuth difference and an elevation difference associated with an object detected in either the SAR or DBS map. The position processor of the system and method of the present invention, however, only inputs the summation output and one of the azimuth difference and election difference. The position processor determines the other of the azimuth difference and the elevation difference by converting the velocity output by the INS into a doppler angle .theta. (the angle between the velocity, a vector, and a line connecting the object and the body) and determining either the azimuth difference or the elevation difference from the doppler angle .theta..

Abstract: A desired signal is received at first and second antennas. Output signals of the first and second antennas are orthogonal-detected by first and second signal conversion circuits and thereby converted into first and second baseband signals. A complex conjugation circuit generates a complex conjugation signal by calculating a complex conjugation of the second baseband signal. The first baseband signal and the complex conjugation signal are multiplied by a multiplier. A direction estimation circuit estimates a direction of the desired signal by effecting an inverse tangent calculation and an inverse cosine calculation on an output signal of the multiplier.

Abstract: A method and apparatus for improving resolution of targets in a monopulse radar beam.

Abstract: A radio transmission system comprises a phased-array radio apparatus for optimizing reception in a multipath transmission environment. In the phased-array radio apparatus, phase shifting is performed after down-conversion of received RF signals. Phase control and beam-forming are simple. By applying a zero-IF or low-IF receiver structure, the complete structure can easily be fully integrated.

Abstract: A method and apparatus for detecting the presence of multipath interference within a radar receiver disposed to form sum (.SIGMA.) and difference (.DELTA.) signals by time-sampling a target return signal is disclosed herein. In accordance with this method there is formed a sequence of complex conjugates (.SIGMA.*) of the sum signals (.SIGMA.). Each of the .SIGMA.* signals is multiplied with an associated one of the .DELTA. signals so as to form a time-sampled sequence of .SIGMA.*.DELTA. signals. A power spectrum representation of the time-sampled sequence of signals .SIGMA.*.DELTA. is then generated, wherein the presence of selected spectral components within the .SIGMA.*.DELTA. power spectrum indicate the existence of multipath interference within the radar receiver. In a particular implementation the .SIGMA.*.DELTA. power spectrum representation is quickly and reliably determined by performing a Fast Fourier Transform (FFT) operation upon the time-sampled sequence of .SIGMA.*.DELTA. signals.

Abstract: A secondary radar uses monopulse reception techniques to improve the estimate of the aircraft position and to improve the reliability of the reply decoding process. Digital signal processing techniques are utilized to replace the analog circuit used in the prior implementations. The secondary radar implements monopulse processing using a half angle phase method wherein the sum and difference signals are encoded in a complete phasor. The detection of the signal and extraction of the azimuth angle data is implemented using a digital receiver concept. The complex phasor is sampled at an intermediate frequency, down converted to baseband and detected. The azimuth angle is computed using arithmetic methods implemented by digital signal processing circuitry.

Abstract: A monopulse signal processor provides target monopulse ratios and thus target angles having an improved accuracy in those situations where a low signal-to-noise ratio subsists and the monopulse ratio is derived from a sequence of pulses. The monopulse ratio value is determined by: ##EQU1## and .SIGMA..sub.Ii is the in-phase component of the sum signal for the i.sup.th pulse, .SIGMA..sub.Qi is the quadrature component of the sum signal for the i.sup.th pulse, .DELTA..sub.Ii is the in-phase component of the difference signal for the i.sup.th pulse, and .DELTA..sub..OMEGA.i is the quadrature component of the difference signal for the i.sup.th pulse.

Abstract: A dual channel monopulse transceiver is described for use at millimeter wavelengths and for the detection of targets for vehicle collision avoidance. A microstrip antenna is located on one side of a plate and a transceiver microstrip circuit coupled to the antenna is located on the other side of the plate. The transceiver includes a reflective balanced mixer, an isolated balanced mixer and a hybrid circuit for connecting the mixers to antenna feed points. Sum and difference signal generating circuits are employed to provide single and split antenna beams for the detection of targets.

Abstract: A system and method that provides for all-weather precision guidance of conventional air-to-surface weapons. The system and method employs a coherent monopulse radar disposed on a launch platform and a noncoherent passive (receive only) radar disposed on the weapon. The synthetic aperture radar generates a synthetic aperture radar monopulse map of an area around the target. The radar is used designate the location of the target, and transmit a sequence of alternating sum and simultaneous azimuth and elevation difference patterns centered on the target. The weapon includes a guidance system and seeker that is responsive to guidance commands transmitted by the synthetic aperture radar. The guidance system and seeker receives reflections of the alternating sum and combined azimuth and elevation difference pattern from the target, and the sum pulse is used by the weapon to acquire and track the azimuth and elevation difference pattern null on the target to fly an optimum trajectory to the target.

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: 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: 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 for correction errors in radar systems that operate using a crossfeed principle (CFR), in which echo signals are directly received from flying objects, such as an aircraft. In particular, the present invention is used in connection with low-flying objects, in which radar signals are indirectly reflected from the surface of the earth to an antenna of the radar system. Correction terms are determined and weighted, using correction factors, so as to improve the capability of the crossfeed radar system to accurately determine the exact elevation of the flying object. The correction factors that are used to improve the accuracy of the radar system are based upon sea state numbers, or Beaufort numbers, which vary in relation to the shape and/or structure of the reflecting surface.

Abstract: Radar apparatus for determining the height of a low-elevation target, the target being illuminated by a transmitter (7) and an antenna (3) via a TR-switch (6). Electromagnetic radiation reflected directly by the target and indirectly by the target via the earth surface is received by the antenna (3) and processed in a sum receiver (9, 10, 11), connected via the TR-switch (6) to the antenna (3), into complex sum signals, and in a difference receiver (12, 13, 14), into complex difference signals. A signal processor (15), receiving the complex sum signals and the complex difference signals, is provided with an algorithm which determines the height of the target. The algorithm enables the determination of the target height while the antenna remains directed at the target.

Abstract: A method of and an apparatus for measuring the null angle in the difference vs. sum pattern and in the difference pattern of a monopulse antenna. The null angle of the monopulse antenna in the radiation pattern is acquired by transmitting an RF signal from a plurality of antenna elements to the monopulse antenna, acquiring the sum signal and difference signals in the directions of the respective antenna elements and acquiring the null angle in accordance with the sum and difference signals. The apparatus comprises a rotator for changing the direction of the monopulse antenna and a transmitting antenna facing the monopulse antenna for transmitting a test signal to the monopulse antenna.

Abstract: In a surveillance radar, a process is disclosed which can determine the angular positions of multiple jammers with the use of a monopulse agile beam antenna. It involves collecting and processing jammer data received via a monopulse antenna, in order to determine jammer location, and to resolve two jammers within the main beam when present. A feature is the use of the ratio of the imaginary and real parts of the difference/sum ratio as a discriminant to select a subset of multiple measurement data points, from which the individual jammer angular locations can be determined, when two jammers are present, by averaging upper and lower percentiles of the real difference/sum ratio data points of that subset.

Abstract: A secondary surveillance radar system in which monopulse processing is used to obtain angle estimation of azimuth bearing, the improvement residing in a precision method, involving a monopulse qualifier signal, for identifying the maximum unambiguous off-boresight azimuth (OBA), while ensuring reduced sensitivity to Omni channel variations; the monopulse qualifier signal is developed from coherently combining the IF limited signals derived from the Sum+JDelta and Delta+jSum signals, such that two amplitude varying signals are created, such signals bearing a direct relationship to the Sum and Difference antenna pattern ratios and being independent of antenna signal power.

Abstract: A phase dependent radar guidance system, the receiver (18) of which separates returns into a channel (22) where returns are summed (S) and a further channel (24) where the returns are differenced (jD). The S and jD signals are combined (26) and formed into two further channels as S+jD and s-jD, both of which are passed through AGC controlled amplifiers (28, 30) into a phase angle detector (32) which provides the target (14) angle .beta. to boresight (20). A test signal is applied to the receiver (18) with jD=O, the output value of the phase angle detector (32) for various values of AGC attenuation are stored by a digital processor (34), and the processor (34) modifies measured target phase value with the stored values to correct for AGC amplifier-induced errors.

Abstract: A monopulse receiver includes a monopulse antenna and arithmetic unit for providing a monopulse sum signal, S, an azimuth difference signal, y, and an elevation difference signal, p, an imbalance correction circuit to provide a first composite signal defined as (y+jp) and a second composite signal defined as (y-jp), wherein j is an indicator of being in quadrature with the monopulse sum signal, and for interleaving the first and the second composite signal for providing a composite difference signal, D, and a combiner for providing a third composite signal defined as [S+D] and a fourth composite signal defined as [S-D].

Abstract: A method of processing in a two-channel monopulse receiver and processor is shown to include the steps of: (a) forming composite signals equal to [S+(p+jy)] and [S-(p+jy)] where S in a monopulse sum signal and p and y are, respectively, pitch and yaw error signals; (b) alternately passing the composite signals through a two-channel amplifier; and (c) separating the components in the resulting amplified composite signals for conventional monopulse processing and smoothing to eliminate the effects of any imbalance (in phase or amplitude) between the channels in the two-channel amplifier.

Abstract: The invention relates to a method for improving the angular resolution of a monopulse radar.Starting from the sum signal S, a direction signal .theta..sub.b, and a signal representing the quadrature angle-error measurement .vertline..epsilon..sub.q .epsilon., the method consists of calculating in a first device 201 a signal .DELTA..theta. representing the wingspan of the target, then of calculating in a second device 202 two measuring signals .theta..sub.A and .theta..sub.B representing respectively the direction of the external limits of the target, as well as a signal Q representing the quality of these measurements and finally of carrying out an adaptive filtering operation on the measurements in a third device 203, in order to obtain filtered estimates for .DELTA..theta., .theta..sub.A and .theta..sub.B.

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: Device for angle measurement for inclusion within a monopulse amplitude comparison radar receiver for particular application within secondary radars. In essence it consists of a log (.SIGMA.) signal comparator (9) against a detection threshold, which is meant to enable further processing; of two-analog-numerical converters (10, 11), a codes (12), receiving outputs .SIGMA. and .DELTA. from converters above, which provides the calculation of target azimuth.

Abstract: Radar systems that operate in accordance with the crossfeed method require an exact balancing of the individual Doppler frequency evaluation channels in the receiver. According to the invention, a special method is used first to make the amplitude levels in the individual channels equal to one another and then to determine and balance the phase differences between the channels. A radar system using this method is also described.

Abstract: An active array system is disclosed with electronic roll stabilization of the difference patterns, and with arbitrary partitioning of the phase scanned aperture with no hardware changes. The array system comprises a large number of radiating elements forming the array, with individual transmit/receive active modules coupled to each radiating element. In each active module, the received signal is amplified and then divided into three signal components. Two of the signal components are passed through a bi-state phase shifter for selectively phase shifting the signal component by 0 to 180 degrees. The selectively phase shifted receive signals are then coupled to the respective azimuth and elevation difference channels. The third signal component is coupled to the sum channel network. The respective sum and difference channels all provide summing functions on the respective sum and difference signals from each module.

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: There are derived from the sum and difference signals of a monopulse radar receiver a pair of signatures that quickly and reliably, e.g., unambiguously, indicates when a target being tracked moves out of the center of the antenna main beam. The sum and difference signals are combined in phase quadrature to form a first vector signature signal. The sum and difference signals are also combined in phase quadrature to form a second vector signature signal so that the phase difference between the signature signals varies with the amplitude of the difference signal. The first and second signatures are compared to detect the phase difference therebetween. Commutated signatures are used to determine the direction of target displacement from the antenna boresight and/or to verify the accuracy of the out of beam indication.

Abstract: A microwave deviation measurement receiver particularly applicable to airborne secondary radars making deviation measurements with two logarithmic amplifiers which increase the reliability of deviation measurements for targets close to the direction of aim of the radar. A programmable phase shifter preferably is controlled to compensate for aircraft movements by shifting the phase of the sum or control signal.

Abstract: The method of the invention, applied for example to estimating the parasite phase .phi..sub.a between the azimuth sum .SIGMA..sub.a and difference .DELTA..sub.a channels, consists in calculating the expressions S=.SIGMA..sub.a .multidot..SIGMA..sub.e * and D=.DELTA..sub.a .multidot..SIGMA..sub.e * for different successive measurements made by the radar, then in calculating the expressions [S.sub.(k+1) -S.sub.(k-1) ].multidot.D*(k) for different successive times k-1, k, k+1 and in averaging the result of this expression or different times k, it being understood that the radar antenna sweeps in azimuth and that the radar wave emitted is polarized circularly, the single pulse azimuth and elevation receivers receiving respectively only one of the circular polarization types: right hand or left hand.

Abstract: A secondary surveillance radar system in which monopulse processing is used to obtain angle estimation of azimuth bearing, involving a monopulse processor, two independent phase detectors in respective A and B channels, the arrangement being such that a log amplifier is provided in each of the respective channels and the outputs of these log amplifiers are coupled to the independent phase detectors, whereby a resultant signal is obtained giving target deviation from boresight in either direction based on differences in phase between signals appearing in the respective channels.

Abstract: The sum and difference ports of a conformal phased array monopulse antenna are fed in such a manner as to correct for the degraded radiation pattern which would otherwise occur as a function of scan angle.