United States of America As Represented by the Secretary of the Air Force

Hazeltine Corporation

US Government As Represented by the Secretary of the Army

Raymond J Masak

Herbert F Baurle

Anthony M Kowalski

Frank M Torre

James J Maune

William F Frost

Raymond J Lackey

Anthony F Kowalski

John F Crush

In a microwave communications link, an antijamming antenna system with enhanced main beam nulling is realized by providing gain in the difference port output of a monopulse antenna compared to the sum port. As a consequence interference signals are nulled out at much closer angles to the desired signal than is the case when the gain is the same in both channels. The gain is introduced when a dominant jammer is detected. Detection of a dominant jammer is identified for the conditions in which the monopulse sum channel power level exceeds the sum of the difference channel power levels and the system processor output signal/noise ratio is unsatisfactory.

Method and means for providing enhanced main beam nulling in antijamming antenna

A beamforming adaptive control loop is simultaneously employed in combination with a null-steering adaptive control loop to enhance the signal/interference ratio resulting in an increase in the messasge quality. The loops may employ temporal processing in which case on-epoch sample/hold filters and off-epoch sample/hold filters form separate loops which enhance the desired signal and cancel the undesired signal, respectively. The correlated output from the beamforming loop is added to the correlated output of the null-steering loop and mixed with the incoming signal.

Beamforming/null-steering adaptive array

In order to recover the original audio modulation samples when using a continuous code change, sampled data, spread spectrum waveform structure, a dedicated message matched filter is used to process data from multiple emitters within the same range interval. The dedicated message matched filter is matched to an incoming signal only at the precise time of the message epoch. The matched filter coding corresponding to the arrival time of message epochs as derived from synchronization acquisition circuitry is rapidly switched so that one dedicated message matched filter can be used to process data from multiple users simultaneously.

Dedicated message matched filter

The amplitude of a signal to be modulated on a carrier wave is sampled every T seconds. The sampled amplitudes are converted into phase representative pulses of pulse rate 1/T. Each phase representative pulse corresponds to the difference between a first phase corresponding to the sampled amplitude and the phase of Nth previous phase representative pulse, where N is an interger greater than 1. The discrete phase representative pulses are phase modulated onto the carrier wave. Conversion is accomplished by detecting the sampled amplitudes, applying the detected amplitudes as an address to a ROM to provide corresponding differential phase information, and modulating the differential phase information onto the carrier. To demodulate the signal from the carrier wave, the carrier wave is delayed for NT seconds and the delayed signals are subtracted from the undelayed signals. The resulting signal is linearly detected by an envelope detector to develop an output signal representative of the original modulating signal.

Differential phase modulation

A beamforming adaptive control loop is simultaneously employed in combination with a null-steering adaptive control loop to enhance the signal/interference ratio resulting in an increase in the message quality. The loops employ spectral processing in which case bandpass filters and notch filters form separate loops which enhance the desired signals and cancel the undesired signals, respectively. The correlated output from the beamforming loop is added to the correlated output of the null-steering loop and mixed with the incoming signal.

Improved gain control in a multiplexed adaptive array processor having main and a reference channel receiver is achieved by means of an AGC circuit controlling the gain of the reference channel receiver over its dynamic range, an AGC circuit slaved to the reference channel receiver AGC circuit controlling the main channel receiver, and a separate AGC circuit controlling the output of the main channel receiver.

Coherent dual automatic gain control system

A hand off integrator apparatus utilizing first and second recirculating integrator units in series to integrate a series of input pulses in order to detect the presence of weak signals in a high background noise environment.

Hand off integrator apparatus for signal detection

An apparatus for cancelling undesired signals affecting an antenna system. The apparatus includes a plurality of adaptive modules. Each module provides sum and difference signals from a pair of antennas in the system. Each difference signal is weighted by an adaptive controller coupled to the difference signal and the apparatus output signal. All sum signals from the modules are sum and all weighted difference signals from modules are summed and the total weighted difference signal is subtracted from the total sum signal to provide an apparatus output. The adaptive controller is a multiplexer associated with each of the difference signals of the modules, a reference receiver receiving a multiplexed information and a correlator coupled to the received information and the apparatus output. The correlator controls the weights affecting each of the difference signals of each module. The output of the subtractor is decoded by a main receiver.

Adaptive array having an auxiliary channel notched pattern in the

A sidelobe canceller using only a widely spaced auxiliary array can lose performance for multiple jammers located at angles corresponding to the grating lobe structure. The degradation is independent of the number of control loops used. A closely spaced auxiliary array cannot resolve and process closely spaced jammers but is less susceptible to grating lobe occurrences. Its performance can degrade for closely spaced jammers while the widely spaced array has the resolution capability required. A dual array approach comprised of both widely and closely spaced subarrays was simulated and tested. Each subarray automatically compensated for the deficiencies of the other. The computer simulations predicted the precise nature and locations of these geometrical conditions when the system was tested. Auxiliary channel preprocessing can successfully be used with the dual array approach to simultaneously minimize the differential level problem for multiple jammers. Without preprocessing of the auxiliary array, little, if any cancellation may be achieved against weaker jammers.

Multiple loop sidelobe canceller

A combined adaptive sidelobe canceller and frequency filter system eliminating the narrow band interfering signals by use of the adaptive frequency and eliminating the broad band interfering signals by the adaptive sidelobe canceller.

Combined adaptive sidelobe canceller and frequency filter system

A radar system having means for effectively eliminating or cancelling intering signals characterized by the side lobes of the radar antenna received signals. An adaptive side lobe canceller system is combined with a frequency selective limiter such that the adaptive side lobe canceller is sampled by the output of the frequency selective limiter to derive a weighting signal from the adaptive control circuit. The weighting signals effectively provide simultaneous cancellation of both broad and narrow band interfering side lobe signals.

Combined side lobe canceller and frequency selective limiter

An adaptive signal processing system for enhancing the signal-to-interfere characteristics on both receive and transmit using an in phase-quadrature correlator to control phase and amplitude adjust circuits located in the antenna signal paths. The amplitude adjustment provides amplitude balance control with variable delay lines between a quadrature hybrid and a sum-difference hybrid. The analog outputs of the correlator are digitized to control incrementally adjustable delay lines of the phase and amplitude circuits in binary steps.

Adaptive steerable null antenna processor

An adaptive signal processing system for enhancing the signal-to-interfere characteristics on both receive and transmit, using an in-phase quadrature correlator to control phase and amplitude adjust circuits located in the antenna signal paths. To increase the dynamic range, automatic gain control circuits are included in the reference and feedback signal paths to the correlator.

Steerable null antenna processor with gain control

A sidelobe canceller in which the undesired signals in the main antenna channel are cancelled at RF using signals from multiple auxiliary antennas, where each auxiliary antenna signal has been weighted in a vector modulator while at RF. The weighting is determined in a single wideband IF loop by multiplexing the multiple auxiliary antenna signals through the same auxiliary receiver, correlator and demodulator. The demodulated output signal from each auxiliary antenna is sampled and retained as a weighting to adjust the vector modulator for the corresponding auxiliary antenna. A timing and control circuit coordinates the multiplexing and sampling functions.

Multiplexing of multiple loop sidelobe cancellers

Multiple interference signals in an electromagnetic wave communication system are individually discriminated against by a beamport sidelobe canceller comprising a multichannel auxiliary system in which spatial filtering of the angular sectors of interest is performed prior to sidelobe cancellation. Each spatial filter of the auxiliary system has its own adaptive control and only those interfering signals appearing in its assigned sector are operated on by that loop. The output of the main communication system receiver is summed with the outputs of the auxiliary system channels to produce a system output and an adaptive control loop feedback signal. The feedback signal initiates the generation of a cancellation signal in any adaptive control loop in which correlation of interference signals occur in both the main communication system received signal and the signal received by the auxiliary system channel to which that loop is connected.

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East Northport, NY, United States of America

Raymond J Masak