An interference-matched notch filter for narrowband RFI suppression in SAR

Abstract

Narrowband radio-frequency interference (NBI) degrades synthetic aperture radar (SAR) images. Frequency-domain notch filtering is a common countermeasure, but a hard (rectangular) notch trades interference rejection against raised sidelobes, and a fixed apodized (tapered) notch cannot suit emitters of different bandwidth. This paper presents a simple, low-complexity notch whose shape is matched to the measured interference spectrum. Based on the classical Wiener idea, it estimates each emitter’s power spectral density from the averaged SAR range spectrum and applies a parametric minimum-mean-square-error gain whose roll-off follows that emitter; the filter is linear, needs no per-scene tuning, and costs about one spectral multiplication per pulse. On a 2-D SAR simulation with emitters of differing bandwidth it gives the lowest point-target peak sidelobe ratio (PSLR; about −15.1 dB), integrated sidelobe ratio (ISLR; about −7.2 dB) and image normalised mean-square error (NMSE; about −7.0 dB) among a hard notch and a fixed apodized notch. The contribution of this paper lies in the per-emitter spectrum-matched notch design and the comparative evaluation of the proposed method’s effectiveness against other approaches.