Abstract: A method and system for are provided for detecting one or more radar targets of interest in the presence of jamming signals. A plurality of sub-arrays are formed from an antenna array. Sub-array beams are adaptively formed so as to point one or more nulls in one or more respective directions corresponding to one or more jammers. A super-resolution technique is applied to determine a count of the one or more radar targets and to determine the corresponding direction of arrival.

Abstract: A radar system receiver having an antenna system adapted to receive a jammer signal from both a direct path and from an indirect path. The direct and indirect paths have both differential Doppler frequency and differential time delay induced phase shifts. The antenna system includes a plurality of antenna elements. A plurality of radar receiver sections, each one having a clutter filter, is provided. Each one of the receiver sections is fed by a corresponding one of the antenna elements. An adaptive jammer canceler is fed by the plurality of radar receiver sections for providing a beam forming network to suppress both the direct and indirect paths of the jamming signal.

Abstract: The present invention describes a system for counteracting countermeasures against radar detection. Two known countermeasures are “phase front tilting” and “isotropic scattering.” The invention accomplishes this counteraction by deliberately producing a tilt in the phase front of the transmitted energy. This causes the phase front tilting countermeasure itself to become a tracking signal source for the radar system. The isotropic scatterer types of countermeasures are insensitive to the phase front of the transmitted energy and hence produce return signals which may be distinguished from a true radar echo return signal which is highly sensitive to the phase front of the transmitted energy. Thus this invention provides a radar system having a high degree of immunity to radar countermeasure devices.

Abstract: A radar system and method for detecting and tracking a target of interest in the presence of interference, wherein the interference emits interfering signals, includes a receiver for receiving the interfering signals directly from the interference. The receiver also receives reflected signals, wherein the reflected signals is the interfering signals reflected by the target of interest. The interfering signals and the reflected signals are compared to detect the target of interest. In one embodiment, the reflected signals and the interfering are cross-correlated. The results of the cross-correlation are used to obtain range, position, and velocity information about the target of interest from a range/Doppler map.

Abstract: A system and method for detecting a radar target of interest in the presence of radar jamming interference include a sub-array beamformer, a sum and difference beamformer, a weight calculator, a composite beamformer, and a monopulse ratio calculator. A plurality of sub-arrays is formed from antenna array element data. Respective sum and difference beams are formed for each of the plurality of sub-arrays. A single weight is formulated from the sum and difference beams, respectively. Composite sum beams are formed in accordance with the sum weights and the sum beams, and composite difference beams are formed in accordance with the difference weights and the difference beams. Composite beams are formed such that at least one null of each of the composite beams is steered toward an interference and a boresight gain of each of the composite beams is maintained.

Abstract: In a radar system, sampled aperture data are received from an antenna array. The sampled aperture data include data that do not correspond to echo returns from a beam transmitted by the antenna. A covariance matrix is generating using the sampled aperture data. An eigenvalue decomposition is performed on the covariance matrix. A direction of arrival is determined from which at least one jammer is transmitting a signal included in the sampled aperture data, based on the eigenvalue decomposition.

Abstract: A radar system and method for detecting and tracking a target of interest in the presence of interference, wherein the interference emits interfering signals, includes a receiver for receiving the interfering signals directly from the interference. The receiver also receives reflected signals, wherein the reflected signals is the interfering signals reflected by the target of interest. The interfering signals and the reflected signals are compared to detect the target of interest. In one embodiment, the reflected signals and the interfering are cross-correlated. The results of the cross-correlation are used to obtain range, position, and velocity information about the target of interest from a range/Doppler map.

Abstract: A method and system for are provided for detecting one or more radar targets of interest in the presence of jamming signals. A plurality of sub-arrays are formed from an antenna array. Sub-array beams are adaptively formed so as to point one or more nulls in one or more respective directions corresponding to one or more jammers. A super-resolution technique is applied to determine a count of the one or more radar targets and to determine the corresponding direction of arrival.

Abstract: A radar system including a blanker and a sidelobe canceler is described including an open loop nulling circuit for introducing one or more nulls in the main beam and a blanker beam. With this arrangement, the blanker can be operated even in the presence of strong sidelobe jamming without the conventional problems attributable to noise amplification. Also described is an antenna configuration for implementing the open loop nulling, including a pair of orthogonal linear arrays. One of the arrays is omnidirectional in azimuth and directional in elevation and the other array is omnidirectional in elevation and directional in azimuth in order to point the main and blanker beams in the direction of jammers. In one embodiment, the radar system further includes a spoofer and the crossed linear arrays process the spoofer signals on transmit and process blanker signals on receive.

Abstract: A wideband adaptive digital beamforming technique for maintaining a high range resolution profile of a target in motion in the presence of jamming utilizes a sequence of adaptively calculated narrowband jamming cancellation weights. The adaptive weights are calculated such that the desired frequency dependent gain is maintained toward the target center. These adaptive weights tend to preserve the range profile quality and low range sidelobes. This technique also tends to eliminate signal cancellation problems as well as adaptive weight modulation effects.

Abstract: A signal processing circuit is disclosed for providing fuze-on-jam capability in a target detecting device, while in the presence of continuous wave or continuous wave noise jammer signals. A target detection system will protect the target detecting device from noise jammers and continuous wave radars or continuous wave jammers by providing a circuit which samples the negative or positive bias produced by the noise modulated CW signal and produces either positive or negative polarity as seen by the antenna. If negative pulses are produced, they will actuate the target detecting gate and guard circuit and after the missile has passed the critical angle of the antenna the phase change will then produce firing in the normal manner. The sampled output is fed into the target detecting mixing circuit and no interference with normal operations of the target detecting device occurs while a fuze-on-jam or CW capability is provided.

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 tracking radar receiver as described herein is relatively invulnerable to image frequency jamming. Partial image-rejection down-converters down-convert RF signals to IF signals in each of various sum and difference receiver channels. Image frequency components of the IF signals exhibit a predetermined amplitude and phase relationship relative to corresponding real frequency components for each of the channels. Thus, phase and amplitude tracking between the various channels is achieved even when image frequency signals are received.

Abstract: A method and system for using the main diagonal elements of the Cholesky factor of the spatial covariance matrix to estimate the number of jammers present, by evaluating the AIC (or other) test function using the Cholesky diagonal elements in place of covariance eigenvalues. The Cholesky factor is often available as a by-product of adaptive beamforming.

Abstract: The present invention relates to a method for the protection of mobile military facilities, in particular military bridges, against target-seeking guided weapons equipped with various threat sensors, wherein the mobile military facilities are equipped with active and passive anti-sensors for detecting a threat by approaching target-seeking guided weapons and computing their trajectories and determining suitable intercept coordinates for deploying countermeasures. Moreover a mobile dirigible launcher furnished with various decoy effective agent ammunitions is provided in the surroundings of the facility to be protected and/or immediately on the said facility.

Abstract: There is provided an autonomous off-board defensive aids system (100) for use with a host craft (102), for example, with combat aircraft or submarines. More particularly, the host craft (102) deploys a plurality of controllable off-board units (104, 106) to counter an offensive threat or to engage in autonomous offensive actions. The controllable off-board units (104, 106) implement active stealth facilities: each off-board unit (104, 106) having a receiver unit for detecting impinging detection pulses, for example radar or sonar pulses, and a transmitter unit for generating an artificial detection pulse profile, for example “spoofing” or masking the presence of the host craft. The controllable off-board units are of two types: tethered (104) and free moving (106). The off-board units (104, 106) can have conventional propulsion apparatus, for instance, propellers, rockets or jets. Off-board units (104, 106) each have control apparatus which allows the off-board units (104, 106) to co-operate.

Abstract: A silent radar system which detects a target and its position without the countermeasure operator located at the target being able to detect the presence of the radar. The silent radar operates by transmitting signals with specific characteristics which allow optimum processing by the radar while taking advantage of the limitations inherent in typical signal receiving equipment. The silent radar transmits low energy per cycle signals which are wideband, purely random noise, e.g. spread spectrum signals.

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: In a jamming cancellation system wherein a balanced modulator receives as two inputs thereto: the desired plus jamming signals, and the AM difference frequency produced by the beating of the desired and jamming signals, jamming suppression, in an environment containing two jamming signals, is achieved by peak detecting the output from the AM difference frequency producing means and applying same directly to the receiver video input or upconverting same to the receiver r.f. frequency and applying same to the system receiver.

Abstract: A coded phase modulation communications system which relates to communications systems in which undesired detectability of the radiated signal is materially reduced, and wherein the vulnerability of the system to interfering signals, such as, intentional jamming signals, is substantially reduced. In the system, a radio frequency communications signal is phase modulated by a random or random appearing, but repeatable pattern of noise signal. The received signal is modulated by an identical noise signal, which when synchronized with the original noise modulation results in erasing the noise, and thereby recreating the original, continuous, communications signal. The noise source of the system is a pseudo noise generator that may be readily synchronized with an identical noise source or sources. The pseudo noise generator provides an apparently orderless noise-like sequence that may be exactly reproduced at the same or at a remote location or locations.

Abstract: A system for instrumenting time sampled predicting interference suppression, particularly in a side-lobe canceller system. Main and auxiliary channel signals are supplied to a canceller loop where correlating weights are sampled just prior to a radar pulse transmission on command of a radar pretrigger pulse. A sampling circuit stores both current and past weights and combines the current weight with the integral of the difference between the current and past weight to form predicting weights over each pulse repetition period. The predicting weights are used to form a translating signal for operating on the auxiliary channel interference signal so that it will cancel the interference in the main channel. By sampling just prior to radar pulse transmission and forming the predicting weights, cross modulation of clutter and antenna scan error can be reduced in order that a side-lobe canceller may be used compatibly with Moving Target Indicators.

Abstract: A radar system (10) which transmits a random noise signal. The transmitted signal is embodied as an electromagnetic signal and is directed at an object or target. The object or target reflects at least a portion of the electromagnetic signal which is returned to the radar system. An image of the electromagnetic random noise signal is stored in memory (16) and compared with the returned modulated signal. Based on the correlation value, a determination is made regarding the object or target. In a particular implementation, the radar system is used in a target detection device (TDD) (10) in order to determine the distance from the target or object to the device and the relative velocity of the target or object and the device. When the target or object reaches a predetermined distance and also satisfies any other system requirements, the TDD (10) initiates a detonation signal which causes detonation of the missile or warhead.

Abstract: A radar receiver adapted to detect and track a narrow band jammer is shown to include logic circuitry adapted successively to sense jamming signals from such a jammer to determine the extant frequency of the speed gate when the amplitude of the automatic gain control signal increases and to determine whether or not the received signals are coherent, and, finally, if the received signals are not coherent, to produce a tracking control signal effective to cause tracking of the narrow band jammer.

Abstract: A radar system including a main antenna and a smaller auxiliary antenna, the main antenna having a radiation pattern with a main lobe and relatively small sidelobes, and the auxiliary antenna having an omnidirectional radiation pattern. A received signal in the sidelobes of the main antenna and the corresponding received signal of the auxiliary antenna are spectrally divided by sets of bandpass filters with the signals of corresponding ones of the bandpass filters being processed to null out a signal such as a jamming signal received via a sidelobe of the main antenna pattern. The processing includes inphase and quadrature detection of a partially cancelled signal with the resulting complex error signal being applied as a modulation of the signal of the auxiliary antenna to be subtracted from the signal of the main antenna to produce the cancelled sidelobe signal.

Abstract: (U) A system for protecting a strategic bomber approaching the field covered by an airborne surveillance radar is shown to include: A search receiver arrangement to detect interrogating pulses from such radar before detection by such radar is possible and to determine the range of such radar and an air-to-air guided missile adapted first to home on the source of the interrogating pulses and then to be guided to intercept by an active radar seeker.

Abstract: A jamming suppression system which includes a plurality of receivers for receiving electromagnetic radiations and a separate notch filter coupled to each receiver for filtering selected frequencies from electromagnetic radiations received by each of the receivers. In accordance with one embodiment of the invention, a spatial combiner responsive to the outputs of each of the notch filters extracts essentially jam-free information from the electromagnetic radiations. In accordance with a second embodiment of the invention, a plurality of spatial combiners, each responsive to the outputs of each of the notch filters, extracts essentially jam-free information from the electromagnetic radiations. The notch filters are adaptive notch filters for on-line selection of their filtering action. One of the notch filters is a master filter and the remainder of the notch filters are slave filters controlled by the master filter.

Abstract: A circuit for use in anti-radar missile seekers or radar counter-measure eivers to convert the signals received from continuous wave radars into pulse signals so that the signals may be more readily detected and can be processed in the same signal processing circuitry used against pulse radars. The received signal is mixed with a frequency swept local oscillator signal, fed to a dispersive delay line and then detected.

Abstract: A method of operating a radar to track echo signals from a target in the presence of a barrage jammer is shown to comprise the steps of actively determining the apparent direction of the combination of echo signals from a target and jamming signals, passively determining the actual direction and average power of a barrage jammer, calculating, from the foregoing, the actual direction of the target and instituting range and angle tracking of the target when the target is clear of the jamming signals.

Abstract: This array antenna with anti-jamming in reception for radioelectrical or ultrasound waves is provided with radiating elements fitted out individually or in groups with amplitude-controlled and phase-controlled passive or active modules enabling aiming at transmission as well as at reception by analog beam-forming. It possesses a reception anti-jamming circuit carrying out successively two reduced, adaptive computational beam-forming operations, one in elevation which is performed on a grouping, in horizontal alignments, of the reception signals of the radiating elements and working on the reception signals by modifying the settings of the controlled modules and the other in relative bearing, performed on a grouping, in vertical alignments, of the signals of the radiating elements that which it phase-shifts and adds up to form a reception channel for the total antenna.

Abstract: An intermediate frequency sidelobe canceller of the kind including a cancellation loop and switch means for sampling and holding correlation weights present in the loop, affording enhanced cancellation and reduced loop lock-on time. This capability is achieved by provision of means for control of the sample-hold switch means so as to limit duration of the sampling interval to an optimum value substantially shorter than the loop stabilization time. Such shorter sampling interval may be either of fixed duration or adaptively controlled in response to one or more loop operating parameters.

Abstract: Apparatus and method for eliminating an interference signal from a desired signal where a difference of polarization exists or can be made to exist. The desired signal is received on a first antenna of appropriate polarization and the interference signal is received via another port of the same antenna or a second antenna polarized ninety degrees away from the first. The signal received via the other polarization is adjusted for amplitude and phase so that all interference will be cancelled when both signals are subtracted in a summing junction. In the case where the interference and desired signals do not have polarization differences, provision is made to change the polarization of the desired signal.

Abstract: Suppression of jamming from multiple sources is achieved by detecting the AM difference frequency produced by the beating of a desired signal and the smaller of the multiple jamming signal with the stronger jamming signal and applying same to one input of a single-sideband modulator while simultaneously applying the received signal (containing both the desired signal and the jamming signals) to the other input to the single-sideband modulator whereby the larger jamming signal is suppressed. The sum and difference outputs of the single-sideband modulator containing the upper and lower sidebands, respectively, of the desired signal plus the smaller jamming signal are each processed by a jamming cancellation circuit to suppress the smaller jamming signal and their outputs combined to receive the desired signal.

Abstract: A radar or GPS receiving system uses an antenna array to produce multiple antenna beams directed toward multiple targets or spacecraft. Stand-off jammers produce signals which tend to be received on the sidelobes of the antenna beams and to disrupt system operation. An array of autonomous or adaptive nullers process the received signals to produce weights which adjust the antenna nulls to direct them toward the jammers. The antenna nulls of one beam pattern are compared with the nulls of other beam patterns. Normal between-sidelobe nulls will not occur at the same angle on all of the patterns, but those nulls generated by the nullers will occur at the same angle. The directions to the jammers are deemed to be those directions in which all beam patterns have nulls.

Abstract: A transceiver system comprises transceivers and a controller in communication with the transceivers. Each of the transceivers comprises an emitter, a receiver operatively connected to the emitter, a primary data path operatively connected to the receiver, a secondary data path operatively connected to the receiver, a statistical unit operatively connected to the secondary data path and the controller and a display device operatively connected to the primary data path.

Abstract: A moving target simulator system for pulse Doppler radar includes a processor for processing received radar signal and transforming the signal into patterned pulses before subjecting the patterned pulses to an 180 degree phase-shift by a phase-shifter. The system also includes a reference signal provided by a corner reflector located in proximity of the simulator. The reference signal and a phase-shifted signal from the simulator are processed by the radar equipped with a phase corrector circuitry to correct a phase drift problem associated with the use of a small antenna with the simulator.

Abstract: A duty dithering method for use with electronic support measures and radar warning receivers, and the like, that provides for improved probability of intercept at low utilization levels. The electronic support measures (ESM) system and radar warning receiver are controlled by a multi-system sensor manager having an ESM scheduler. In accordance with the present method, a maximum duty cycle is chosen for the ESM system. The chosen duty cycle is allocated to the ESM system each frame by the ESM scheduler. At the beginning of each frame, the ESM scheduler picks a random offset and subtracts it from the maximum duty to compute an ESM duty for that frame. The ESM scheduler commands data collections based on the computed duty for that frame. This step is repeated each frame.

Abstract: Disclosed are global navigation satellite system (GNSS) receivers, including digital spatial nulling arrays, and a method of providing antenna pattern outputs using the same. The digital spatial nulling array receives multiple antenna element inputs. A fast Fourier transform (FFT) is applied to the multiple antenna element inputs to obtain frequency domain representations of the multiple antenna element inputs. The antenna pattern outputs are provided by the spatial nulling array as a function of the frequency domain representations of the multiple antenna element inputs.

Abstract: Apparatus for steerable nulling of a radiation pattern of a main lobe and at least one side lobe with at least one null point produced by an antenna array of n elements relative to wideband radio frequency signals having a carrier wave modulated with pulse signals, while receiving the radio frequency signals from, or transmitting to, a desired station and at least one interfering station. An interference rejection processor (IRP) that has n inputs, each connected to a respective element of the antenna array, is connected between the receiver or transmitter and the antenna array. The IRP steers the effect of the antenna radiation pattern such that the at least one null point substantially corresponds to the reception of the radio frequency signal from, or transmission to, the interfering station. The antenna array has an aperture bandwidth, E, such that the IRP is implemented using only phase delay of the radio frequency signals to steer the radiation pattern.

Abstract: A mobile communication system aiming at immediately recovering from radio disturbances which are frequently caused in a communication device mounted on a mobile unit. This mobile communication system is provided with an antenna for transmitting and receiving an electromagnetic wave, a tracking device for adjusting a pointing direction of the antenna to a direction in which an electromagnetic wave arrives, a receiving device for demodulating a received electromagnetic wave, a transmitting device for modulating information, which is to be transmitted, to an electromagnetic wave, a handset for displaying information to a user and for receiving an instruction from a user, and a control unit for controlling the tracking device, the receiving device, the transmitting device and the handset. Further, the control unit forming the heart of this system has a countermeasure device, a display unit and a fault inferring device.

Abstract: Radar apparatus provided with a transmitting unit (1), having a transmit phase shifter for providing each transmitted pulse in a burst with a selected phase shift, and a receiving unit (7), having a receive phase shifter (9) for cancelling the selected phase shift upon reception. This enables unimpeded radar transmissions and causes an operational repeater jammer to be misled.

Abstract: Monopulse radar operation is improved by nulling a single mainlobe jammer and multiple sidelobe jammers while maintaining the angle measurement accuracy of the monopulse ratio. A sidelobe jammer cancelling adaptive array is cascaded with a mainlobe jammer canceller, imposing a mainlobe maintenance technique or constrained adaptation during the sidelobe jammer cancellation process so that results of the sidelobe jammer cancellation process do not distort the subsequent mainlobe jammer cancellation process. The sidelobe jammers and the mainlobe jammer are thus cancelled sequentially in separate processes.

Abstract: This radar incorporates a single channel, two-dimensional correlator, providing simultaneous correlation in the range/doppler plane. In conventional radar processors, separate channels are used to measure range and doppler. Range track is normally established first and the range signal is then used to enable, or correlate with the doppler channel. In this invention, this correlation is performed simultaneously in a single channel and truly represents the combined ambiguity function, rather than an attempt to merge two separate ambiguity functions. A purely random sequence of binary bits (+1 and -1's) is used to control the phase of each segment in the transmitted signal (either pulse or CW) as opposed to systems using pseudo-random sequences generated by various means such as linear shift register generators. A digital random number generator is used to produce a set of purely random numbers which, when applied to a rule, generates a random sequence of binary bits, plus or minus 1's (.+-.

Abstract: A radar apparatus that is provided with auxiliary antennas (5, 10) of an omnidirectional nature. In addition to customary ECCM applications, such as side-lobe suppression and side-lobe blanking, the auxiliary antennas (5, 10) are also used for the emission of frequency-shifted pulses which are emitted simultaneously with radar transmitter pulses. To this effect, the radar apparatus is provided with auxiliary transmitters (8, 13). Furthermore, auxiliary receivers (6, 11) have been provided for analyzing the responses of jammers to the frequency-shifted pulses.

Abstract: Method and apparatus for enabling a pulse echo radar to generate a false signal in both time and frequency based passive Doppler ESM location systems. The latter false signal causes the ESM system to mislocate the radar. The radar's reference oscillator frequency is varied to create false passive Doppler information at an intercept receiver. These variations are predetermined changes in RF and PRF frequencies for the radar and are relatively small compared to those frequencies.

Abstract: A method and apparatus for controlling the output characteristics of a radar emitter for thereby preventing the location of the emitter using Doppler techniques. The emitter's RF frequency and PRF are under the control of a random signal generator which causes the emitter to emulate common signal corrupting influences.

Abstract: A radar jamming detection system is suitable for recognizing and distinguishing the presence of jamming and, particularly, terrain bounce jamming. The radar system includes a transmitter and a receiver. The receiver receives true radar skin return signals, in addition to ground clutter signals and jamming signals. The true radar skin return signals and ground clutter signals are recognizable in accordance with a predetermined receiver passband. Estimated target location, velocity and frequency data, as provided by a cueing radar, is used to set up the receiver passband for the radar detection system. Ground clutter range and angle measurements are used to determine an estimated ground range at the jammer angle, which is then compared with the cue range to determine if the received signals are terrain bounce jamming signals.

Abstract: Aircraft survivability embedded data recorder for threat data. The embedded threat data recorder stores active threat data generated by aircraft survivability equipment sensors. Threat data from a radar warning receiver, a pulsed radar jammer, continuous wave radar jammer or missile approach detectors are recorded by the embedded threat data recorder. The threat data for each sensor is correlated between each sensor to ensure that redundant threats are eliminated. The threat data recorder represents the recorded threats on a display for mission briefing, evaluating countermeasure effectiveness, or identifying new threats. The embedded threat data recorder also provides downloading of threat data into a threat data transfer cartridge for use in off-line threat analysis. Data can be provided to other platforms, satellites and ground base stations. Data can be recorded on a multifunction display and data compression techniques may be used. The tape may also be played back in the aircraft.

Abstract: A new adaptive interference technique is disclosed which not only increases the cancellation bandwidth but also reduces the convergence time for the adaptive process. This new technique departs from the prior art in adaptive interference cancellation in that an estimate of the interference arrival direction coupled with a predetermined antenna response is used to establish the weight settings in the adaptive cancellation circuitry. This circuitry incorporates variable true time delay components to achieve interference cancellation over a broad bandwidth with a rapid convergence time.

Abstract: Received IFF reply-frequency signals are examined to determine whether they re being interfered with by enemy sources, and indication of the extent of detected interference is provided.The number of correct replies received from selected range bins surrounding and including the center one in which a target leading edge is first declared is counted and compared with the count of the number of friend-accept decisions made based on replies from the selected range bins. The level of interference is then indicated by the ratio between the two counts.

Abstract: Apparatus and method for eliminating an interference signal from a desired signal where a difference of polarization exists or can be made to exist. The desired signal is received on a first antenna of appropriate polarization and the interference signal is received via another port of the same antenna or a second antenna polarized ninety degrees away from the first. The signal received via the other polarization is adjusted for amplitude and phase so that all interference will be cancelled when both signals are subtracted in a summing junction. In the case where the interference and desired signals do not have polarization differences, provision is made to change the polarization of the desired signal.