Kai-Bor Yu

Adaptive digital beamforming for angle estimation in jamming

A radar digital beamforming (DBF) architecture and processing algorithm is described for nulling the signal from a mainlobe electronic jammer and multiple sidelobe electronic jammers while maintaining monopulse angle estimation accuracy on the target. The architecture consists of a sidelobe jamming (SLJ) cancelling adaptive array (AA) followed by a mainlobe jamming (MLJ) canceller. A mainlobe maintenance (MLM) technique or constrained adaptation during the sidelobe cancellation process is imposed so that the results of the SLJ cancellation process do not distort the subsequent mainlobe cancellation process. The SLJ signals and the MLJ signals are thus cancelled sequentially in separate processes. This technique was developed for improving radar processing in determining the angular location of a target, and specifically for improving the monopulse technique by maintaining the accuracy of the target echo monopulse ratio in the presence of electronic jamming by adaptive suppression of the jamming signals before forming the monopulse sum and difference beams.

Adaptive digital beamforming radar for monopulse angle estimation in jamming

This paper describes a digital beamforming architecture for nulling a mainlobe jammer and multiple sidelobe jammers while maintaining the monopulse angle estimation accuracy. It involves two-stage processing using adaptive digital beamforming followed by a mainlobe jammer canceller. A mainlobe jammer blocking matrix and constrained adaptation are employed during the adaptive sidelobe cancellation so that the results of sidelobe jammer cancellation process do not distort the subsequent mainlobe cancellation process. This technique is developed to determine the angular location of a target by maintaining the estimation accuracy of the monopulse ratio in the presence of jamming.

Phase-only nulling for transmit antenna

This paper describes a technique for transmit antenna nulling for low-cost large sparse phased array radar system. Radar system described includes an array of elemental antennas, each with a transmit/receive (T/R) module. The T/R modules are operated at or near maximum output to achieve maximum CD-to-RF efficiency. A phase controller controls the phase shift, which are imparted by each module to its signal, to form a mainbeam and its associated sidelobes. A perturbation phase generator adds phase shifts computed, to form wide nulls in the sidelobe structure. The nulls are achieved at very minimal loss of gain, in the order of fraction of a dB. The speed of obtaining these nulls in real time allows a rapid steering of these nulls in a hostile environment. The thinned aperture allow designing a light weigh mobile system. In radar context, these nulls may be placed on a source of ground clutter, a set of jammers or a set of undesirable radio sources.

Fast recursive subspace updating for detection and angle estimation of multiple sources

This paper is concerned with detection of a number of sources and estimation of their corresponding direction-of-arrival using eigenvalue decomposition updating with subspace structure constraint. The covariance matrix is a low rank matrix plus a noise diagonal matrix. In addition to cleaning up the data, the subspace constraint enables the author to develop an efficient algorithm for updating the principal subspace and the noise eigenvalue.<<ETX>>

Adaptive digital beamforming architecture and algorithm for nulling mainlobe and multiple sidelobe jammers

This paper describes a digital beamforming architecture for nulling a mainlobe jammer and multiple sidelobe jammers while maintaining the angle estimation accuracy of the monopulse ratio. A sidelobe jammer canceling adaptive array is cascaded with a mainlobe jammer canceller, imposing a mainlobe maintenance technique or constrained adaptation during sidelobe cancellation process so the results of sidelobe jammer cancellation process do not distort subsequent mainlobe cancellation process. The sidelobe jammers and the mainlobe jammer are thus cancelled sequentially in separate processes. This adaptive digital beamforming technique is for improving radar processing for determining the angular location of a target, and specifically to an improvement in the monopulse technique so as to maintain accuracy of the monopulse ratio in the presence of jamming by adaptive suppression of jamming before forming the sum and difference beams.

Subarray-based phase-only transmit nulling for jamming and clutter suppression

In this paper we describe a method of obtaining nulls in a phased array system using sub-array based phase-only nulling concepts. Phase-only nulling in phased-array antennas is appealing because the phase shifters can be employed for the dual purpose of beam-steering and nulling of unwanted interference such as jamming, radio frequency interference and clutter. The technique is applicable to transmit as well as receiver nulling in the situation when the amplitude control is not available. The application here is on transmit nulling for jammers decoying and surface clutter suppression in the upper beams. Instead of phase of the entire array, a small set of sub-arrays on the periphery of the array are considered. This implementation allows minimal modification of the phase control structure of the phased array system. Phase-only nulling also has an obvious advantage for transmitting nulling if we want to weight uniformly for maximum output. The problem is solved by formulating it as an optimization problem with side constraints. The method is quite general and can be applied to symmetric as well as non-symmetric arrays with real or complex beams. Based on the analysis the system is then designed and results illustrated for a case similar to the proposed advanced Aegis system. The system simply consists of sub arrays which can be part of the main array clustered together, each cluster receiving only a single phase-change instruction for nulling in presence of jamming, in real time, involving very minimal computation, once the location of jammers are determined. The null-depths achieved shows a performance of about 50 dBs or more. Presently there are many radars which can b represented as circular arrays, with minor modifications, can be retrofitted with hardware for nulling in presence of multiple jammers or to suppress clutter.