Abstract: A radar system and method for maintaining radar performance of radar system in jammed environment are provided. The radar system has main antenna arrangement for transmitting and/or receiving electromagnetic waves. Main antenna arrangement includes at least one main antenna element and at least one main electronics module for transmitting and/or receiving signals to/from at least one main antenna element. The system has auxiliary antenna arrangement for transmitting and/or receiving electromagnetic waves, auxiliary antenna arrangement includes at least one auxiliary antenna element and at least one auxiliary electronics module for transmitting and/or receiving signals to/from the at least one auxiliary antenna element. System has a controller connected to main antenna arrangement and to auxiliary antenna arrangement. Controller is configured to transmit first radar waveform from main antenna element, and transmit second radar waveform from auxiliary antenna element.

Abstract: A novel and useful system and method by which radar angle and range resolution are significantly improved without increasing complexity in critical hardware parts. A multi-pulse methodology is described in which each pulse contains partial angular and range information consisting of a portion of the total CPI bandwidth, termed multiband chirp. Each chirp has significantly reduced fractional bandwidth relative to monoband processing. Each chirp contains angular information that fills only a portion of the ‘virtual array’, while the full virtual array information is contained across the CPI. This is done using only a single transmission antenna per pulse, thus significantly simplifying MIMO hardware realization, referred to as antenna-multiplexing (AM). Techniques for generating the multiband chirps as well as receiving and generating improved fine range-Doppler data maps. A windowing technique deployed in the transmitter as opposed to the receiver is also disclosed.

Abstract: A novel and useful system and method by which radar angle and range resolution are significantly improved without increasing complexity in critical hardware parts. A multi-pulse methodology is described in which each pulse contains partial angular and range information consisting of a portion of the total CPI bandwidth, termed multiband chirp. Each chirp has significantly reduced fractional bandwidth relative to monoband processing. Each chirp contains angular information that fills only a portion of the ‘virtual array’, while the full virtual array information is contained across the CPI. This is done using only a single transmission antenna per pulse, thus significantly simplifying MIMO hardware realization, referred to as antenna-multiplexing (AM). Techniques for generating the multiband chirps as well as receiving and generating improved fine range-Doppler data maps. A windowing technique deployed in the transmitter as opposed to the receiver is also disclosed.

Abstract: Techniques are disclosed for determining the presence of pulse jams in an identification friend or foe (IFF) system. In an embodiment, a plurality of jamming pulse rates are determined. Each of the plurality of jamming pulse rates is a count of jamming pulses entering the IFF system during a corresponding integration period. Each of the plurality of jamming pulse rates is a count of jamming pulses associated with non-valid signals entering the IFF system. An average jamming pulse rate is computed based on the plurality of jamming pulse rates. The average jamming pulse rate is then compared against a pulse jam threshold to determine whether a pulse jam is present (or not present) in the IFF system.

Abstract: A technology is provided for reducing pulsed radio frequency interference. The GPS signal may be received at a GPS device. The GPS device may include a GPS receiver. The GPS signal may include a plurality of sign and magnitude bits. Pulsed RFI may be detected in the GPS signal based on samples of the magnitude bits in the GPS signal. The pulsed RFI received at the GPS receiver may be reduced by communicating a blank signal when the samples of the magnitude bits indicate the pulsed RFI.

Abstract: Anti jamming system comprising a tunable negative jamming signal feedback loop for feedback suppression of a received jamming signal, including an receiver receiving an jamming signal followed by a replica jamming signal generator for generating an replica jamming signal. The receiver comprising a zero IF PLL receiver having a synchronous demodulator and a phase detector, signal inputs thereof being coupled to said input means and carrier inputs coupled to in-phase and phase quadrature oscillator outputs, respectively, of a local voltage controlled oscillator (VCO), said VCO receiving a tuning control signal for tuning the zero IF PLL receiver at the carrier frequency of the jamming signal. The VCO is included in a phase locked loop (PLL) comprising subsequent to the VCO, said phase detector and a loop filter.

Abstract: Anti jamming system comprising a tunable negative jamming signal feedback loop for feedback suppression of a received jamming signal, including a receiver receiving an jamming signal followed by a jamming signal replica generator for generating an replica jamming signal. The receiver comprising a zero IF PLL jamming signal receiver having a synchronous demodulator and a phase detector, signal inputs thereof being coupled to said input means and carrier inputs coupled to in-phase and phase quadrature oscillator outputs, respectively, of a local voltage controlled oscillator (VCO), said VCO receiving a tuning control signal for tuning the zero IF PLL jamming signal receiver at the carrier frequency of the jamming signal. The VCO is included in a phase locked loop (PLL) comprising subsequent to the VCO, said phase detector and a loop filter.

Abstract: Techniques for detecting jammer signals in a received signal are described. In one aspect, high-speed current mirror resistive compensation circuits and output impedance boosting circuits are utilized to increase amplifier bandwidth in an improved wideband amplifier circuit. In another aspect, a dual transistor configuration including common source topology, averaging capacitors and a comparator circuit is utilized to improve the sensing of signal peaks in a peak detector block, which can be used together with the wideband amplifier circuit and a digital jammer detection circuit to detect jammer signals. The digital jammer detection circuit aids in the determination of the presence of jammer signals within the received signal, the determination of which may be variable due to programmability of the digital jammer detection circuit as described.

Abstract: The present invention is a dramatically enhanced RF link for low-data-rate applications (1-100 bps), using one or more transmitters to communicate with one or more receivers, at dramatically enhanced ranges. The receiver of the present invention can rapidly search, detect, and lock in on narrow band signal transmissions, that may be present in a much larger frequency band and which may be changing frequency during the duration of the message. These receivers enable ultra-low noise floor detection of longer range, more highly attenuated, signal transmissions, by decreasing the receiver bandwidth.

Abstract: A hybrid serial/parallel bus interface has a data block demultiplexing device. The data block demultiplexing device has an input configured to receive a data block and demultiplexes the data block into a plurality of nibbles. For each nibble, a parallel to serial converter converts the nibble into serial data. A line transfers each nibble's serial data. A serial to parallel converter converts each nibble's serial data to recover that nibble. A data block reconstruction device combines the recovered nibbles into the data block. The data block is employed by a gain controller.

Abstract: A method for passively detecting the presence of radar signal emitters, in which an ESM unit receives radar signals with a number of antennas, each antenna covering a sector of the surrounding terrain. In order to conserve bandwidth, a technique is used, in which receiving channel is slit into a number of sub-bands. Each sub-band is converted to an IF channel. The individual IF channels are combined into a common IF channel in an adder. This process is repeated once more in order to bring the signals down to baseband, where they are digitized and processed to find the direction to and the identity of the emitter source. A number of ESM units are connected to a control center. In the control center the position of the radar emitter is determined by triangulation. In addition, the identity of the emitter is determined by comparison with known emitter signatures stored in a database.

Abstract: A method is provided for more accurate and reliable sensing of phenomena that are potentially obscured by noise, spoofing or jamming, that is deliberate attempts to obscure the phenomena by false signals or noise in response to the stimuli being provided and/or a detector being activated.

Abstract: A method and apparatus for limiting the effect of interfering transmission on a Global Positioning System (GPS) receiver is disclosed. A first mode of operation of the GPS receiver is provided wherein the AGC of the receiver is operated in a linear state. A second mode of operation of the GPS receiver is provided wherein the AGC of the receiver is operated in a non-linear state. A first signal is provided indicating a presence of a jamming signal. In response to the first signal the GPS receiver is switched from the first mode of operation to the second mode of operation.

Abstract: This invention relates to radar signal processing. In particular, this invention concerns signal processing of agile Pulse Repetition Time (PRT) sampled signal transmitted using spread spectrum technique. This invention solves, in particular, the incompatibility between Doppler processing and spread spectrum such providing an improved anti-jamming technique without narrowing the Doppler range. The method for deconvolution comprises combining the pulses with the same carrier in a burst, transforming the obtained signals from time to frequency domain, and deconvolving the obtained spectra. In a first embodiment of this invention, such a deconvolution method is adapted to irregular PRT sampled signal comprises an irregular samples to regular zero-padded samples conversion step between the combination and the transformation steps.

Abstract: The invention relates to a method of interference suppression in a radar system (10) and also to a system (10) operating according to the method. The system (10) incorporates a first antenna (40) and associated electronic circuits for emitting interrogating radar radiation towards a remote scene (S). Moreover, the system (10) also incorporates a second antenna (45) and associated electronic circuits for receiving interrogating radiation reflected from the scene (S) and generating correponding first and second processed signals. The first and second processed signals correspond to a broader main beam response of the antenna (45) and to a narrower main beam response thereof respectively. By mutually comparing the first and second processed signals, the system (10) is operable to identify those second processed signals affected by interference from the scene (S).

Abstract: An apparatus for electronic warfare signal simulation which is used in an external test system to simultaneously test a plurality of “victim” communication systems for vulnerability to jamming. The test system includes a remote radiator of a signal free of jamming effects, and a remote radiator of one or more radio frequency control signals which represent one or more predetermined jamming threats in the low and mid bands.

Abstract: This invention relates to radar signal processing. In particular, this invention concerns signal processing of agile Pulse Repetition Time (PRT) sampled signal transmitted using spread spectrum technique. This invention solves, in particular, the incompatibility between Doppler processing and spread spectrum such providing an improved anti-jamming technique without narrowing the Doppler range. The method for deconvolution comprises combining the pulses with the same carrier in a burst, transforming the obtained signals from time to frequency domain, and deconvolving the obtained spectra. In a first embodiment of this invention, such a deconvolution method is adapted to irregular PRT sampled signal comprises an irregular samples to regular zero-padded samples conversion step between the combination and the transformation steps.

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 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 weaker signal receiving system inclusive of stronger nearby-sourced interference signal cancellation capability. Stronger interference signal cancellation is accomplished by actively canceling or subtracting from the received signal an intermediate signal in which the weaker signal has been attenuated but the stronger signal remains. Attenuation of the weaker signal in this intermediate signal is accomplished in a feedback loop arrangement by an amplitude-responsive signal processing element embodied from for example a ferrite material such as yttrium iron garnet disposed in a physical wave propagating and wave amplitude sensitive film. The cancellation or subtracting is accomplished using received signals and without need for a direct output sample of the stronger signal at its source. Military aircraft use of the disclosed system in the microwave and other spectral regions with transmission mode as opposed to reflection mode signal amplitude discrimination by the ferrite device is included.

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: The invention relates to an antenna installation with an omni-directional antenna (M) and with an auxiliary antenna (A1) the reception signals from which can be combined in respect of amplitude and phase in such a way that a reception miniumu is produced in a desired orientation in space.

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 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 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: An automated interactive antenna patterning apparatus depicts adaptive array antenna patterns and selects adaptive antenna array characteristics. The apparatus comprises an antenna modeling means building an adaptive antenna description, representing a number of antenna elements, means for determining angle-of-arrival, means for rank-ordering, means for sorting, means for antenna patterning and data output means providing composite antenna patterns for each array receiver. The adaptive antenna patterning apparatus better determines adaptive null steering antenna patterns produced in the presence of numerous interference sources.

Abstract: The device, a microwave pulse signal amplifier, includes an input (E), designed to be connected to a wideband reception head (A, H) suitable for picking up pulse emissions, on which continuous emissions can be superposed, a detection stage (1), connected to this input (E), and providing a rectified signal (SP1), and means for processing (2) the rectified signal (SP1) to establish a rectified pulse signal (SP4), rid of at least part of the effects of possible continuous emissions. The level of the continuous emissions is evaluated by a feedback loop (20, 21) activated (22) when there are no pulse emissions, and is subtracted from the level of the rectified signal (SP1).

Abstract: A plurality of threshold detectors is provided to pass analog signals of predetermined and varying threshold values. An analog to digital converter converts these analog signals to binary 1s and 0s. A target detected on each radar beam sweep is a 1 and no target is a 0. These binary numbers are then stored in a reversible up-down counter. At the first signal received, the counter counts up on hits (binary 1) and counts down on misses (binary 0). When the contents of the counter reaches a predetermined count, a target's leading edge is declared. At this time, the counter is then reset and proceeds to count up on misses and down on hits until the aforesaid predetermined count is attained, wherein a trailing edge is then declared.

Abstract: A Reduced Radar Cross-Section RF Seeker Front-End interrogates a potential arget by issuing interrogation radiation toward the target and receiving and analyzing a portion of the radiation that reflects back from various surfaces of the targeted object while, at the same time, the Front-End reduces the likelihood of its own discovery by the enemy. The Front-End accomplishes the reduction by absorbing radiation directed toward it by an enemy radar or anti-tactical missile rather than allowing the radiation to be reflected back. Such absorption greatly diminishes the availability of signature reflection that belligerents rely on to identify hostile forces on the battlefield.

Abstract: A soliton rejection filter circuit is provided, for use in RF signal procing, for isolating a low level signal in the presence of stronger nearby interfering signals and detecting its modulation over a wide communication bandwidth centered at a relatively low RF frequency. The soliton filter circuit includes a nonlinear transmission line and a filter circuit.

Abstract: A technique for improving sidelobe canceller performance by blocking the canceller output signal upon sensing reduced main channel interference accompanied by an increased sidelobe canceller output. Two signal processing networks form the difference between successive output signals from a radar antenna and sidelobe canceller respectively. The difference signals are multiplied together and the product used to control passage and preclude utilization of the canceller output signal when reduced jamming interference occurs.

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: Two wide dynamic range detection circuits are disclosed, which are capable of detecting low-level desired signals in the presence of nearby strong interfering signals. Each circuit includes an attenuator scheme for attenuating the interfering signal while passing the desired signal. The first attenuator scheme uses a YIG filter in combination with an automatic gate arrangement. The second attenuator scheme uses a two-channel arrangement. The first channel uses a chirp-Z processor to derive a pulse-type transform signal in response to the strong interference signal. The second channel includes a YIG filter followed by a programmable notch filter which is controlled by the interference-signal pulse from the first channel. Following the programmable notch filter in the second channel is a chirp-Z processor followed by a gate arrangement wherein the gates are switched "OFF" under control of the interference-signal pulse from the first channel.

Abstract: Improved radar system performance in a jamming environment is achieved by detecting the AM difference frequency produced by the beating of the desired radar signal with the jamming signal and applying same to one input of a balanced modulator while simultaneously applying the received signal (containing both the desired radar signal and the jamming signal) to the other input of the balanced modulator whereby the output from the balanced modulator contains the desired signal but not the jamming signal.

Abstract: Disclosed is a real time interference signal rejection circuit which utils a conventional chirp-Z analyzer to generate a critical number and stop a counter circuit. The critical number is then read by a microprocessor which calculates new tap values from a set of predetermined tap values to reprogram a programmable filter.

Abstract: A process for cancelling the effects of noise jamming in a radar system having a dual-polarization monopulse antenna, a computer processor, and target detection algorithms, wherein the noise jamming produced by a hostile electronic countermeasure on a target is cancelled so as to detect the target in the optimum detection channel. The process consists of the steps of receiving signals from multiple monopulse polarization aperture combinations of the radar antenna, sampling the signals from the radar antenna, digitizing the sampled signals, calculating combination values based upon the samples of the digitized signals, computing several potential target detection channel signals based upon the combination values and samples of the digitized signals, applying the detection channel signals to the computer processor and selecting the optimum detection channel signal for detection of the target using the computer processing whereby the signal is then applied to target detection algorithm of the radar processor.

Abstract: An improved radar receiver having side lobe blanking and coherent side lobe cancellation circuits in the main receiver channel and a control arrangement that overcomes the conventional problem that the side lobe blanking circuit will also blank a noise jammer signal even after the coherent side lobe canceller circuits have acquired the jamming energy. In this system, the side lobe blanking circuits are mechanized with a logarithmic amplifier and with a fast time constant circuit in an auxiliary receiver channel. The fast time constant is selected to match or be slightly longer than the acquisition time constant of the coherent side lobe cancellers. This implementation allows the side lobe blanking circuits to be energized at all times, thus simplifying the operational control of the system. In some arrangements in accordance with the invention the fast time constant may be varied as a function of the amplitude of the jamming signal in the main channel.

Abstract: A method and apparatus for communicating radio frequency signals that may reduce the susceptibility of the signals to jamming. A digital voice signal may be interleaved and transmitted with error correction signals related to the voice signal. The transmission may use frequency hopping with each hop including appropriate synchronization signals, data signals and error correction signals. The received signal at the receiver portion of the signal may contain means for removing both nonexcisable and excisable interference. The nonexcisable interference may be identified and removed by (1) assuming different jamming patterns, (2) decoding to resolve the received signals for each of the assumed jamming patterns, and (3) voting all of the resolved signals to determine which assumed jamming pattern produces the best results. An adaptive filter for removing excisable jamming may applied when such jamming is detected.

Abstract: A radar apparatus is provided with a jamming indicator (11), the jamming indicator (11) having the same bandwidth as the preselector filter (15) of the radar receiver (5).

Abstract: A real-time rejection circuit for passing low level desired signals in the resence of one or more strong, interfering signals. A chirp-Z transform system separates the various frequency components of a received signal into frequency segregated time domain signals. A power splitter separates the time domain signal into two paths. One path includes a modulator or switch that is normally biased "ON" for passing the time domain signal. The second path includes a diode detector that produces pulses of sufficient strength when a strong interfering component is present to override the bias and turn the modulator "OFF" for a sufficient period of time to attenuate the unwanted frequency components in the other path. The modulator output will primarily contain the low level desired frequency components that are passed through an inverse transform device for producing a frequency domain signal of the desired signal uncorrupted by unwanted signals.

Abstract: The method consists in the step of masking the energy influence of the aliased spectrum of a jammer received in the useful band of each of the reception channels of a radio station during a determined time interval surrounding the change-over instant of each antenna. The masking is done either by means of attenuators with diodes placed at the input of each of the reception channels and controlled during the determined time interval or by memorizing, at least during the time interval, the gain of the intermediate frequency amplifiers before the change over takes place, by opening the automatic gain control loop of the intermediate frequency amplifiers to stabilize the gain of each amplifier, during the change over, at its memorized gain value.

Abstract: A method and a device for reducing the power of jamming signals received by the secondary lobes of the main antenna AP of a radar transmitting at a random frequency f.sub.E (n), with which is associated a number of secondary antennas ASl, . . . ASN. The signals used for the calculation in circuit (10) of the weighting coefficients (Wl to WN) to be applied to obtain a signal resulting from the weighted linear combination of the secondary signals Dl, . . . DN to be subtracted from the signal Do in the main channel (VPD) relative to the transmission frequency f.sub.E (N+1) are those (V.sub.0, V.sub.1, . . . V.sub.N) processed in the main and secondary auxiliary channels (VPA, AsAl, . . . ASAN) relative to the transmission frequency f.sub.E (n+1) of the next recurrence train during the period of radar reception of the recurrence train corresponding to the transmission frequency f.sub.E (n) for the jammed range slots selected by circuit (15).

Abstract: A first embodiment includes a set of diffraction gratings on the face of a wheel, each grating being set at an angle to select a different spectral line. The wheel is rotated, and as each grating moves into the end-reflector position of the laser's optical path, the laser is fired. Alternate embodiments include a small spinning fold mirror that reflects the beam in a circle about the axis of the laser.

Abstract: A short pulse radar receiver having a detector with a threshold automatically adjustable with the level of noise and interfering signals. Interfering signals at signal levels which exceed the maximum for which a threshold may be achieved to prevent a false alarm are attenuated prior to coupling to the variable threshold detector by an attenuator variable automatically in accordance with the received signal level.