ARRAY PATTERN DISTORTION AND REMEDIES IN SPACE-TIME ADAPTIVE PROCESSING FOR AIRBORNE RADAR

Space-time adaptive processing (STAP) for airborne early warning radar has been a very active area of research since the late 1980's, An air borne rectangular planar array antenna is usually configured into suba rrays and then partial adaptive processing is applied to the outputs o f these subarrays, In practice, three kinds of errors are often encoun tered, i.e., the array gain and phase errors existing in each element, the channel gain and phase errors, and the clutter covariance matrix estimation errors due to insufficient secondary data samples, These er rors not only degrade the clutter suppression performance, but also ca use the adapted array patterns to suffer much distortion (high sidelob es and distorted mainbeams), which may result in the rise of false-ala rm probability and make the adaptive monopulse tracking and sidelobe b lankering more difficult, In this paper, the causes of the above three kinds of errors to array pattern distortion are discussed and a novel quadratic soft constraint factored approach is proposed to precisely control the peak sidelobe level of adapted patterns. The soft constrai nt factor can be determined explicitly according to the peak sidelobe level desired and the known or desired tolerant error standard deviati ons. Numerical results obtained by using high-fidelity simulated airbo rne radar clutter data are provided to illustrate the performance of t he proposed approach, Although the method is presented for STAP, it ca n he directly applied to the conventional adaptive beamforming for rec tangular planar arrays used to suppress jammers.