A Costas-Based Waveform for Local Range-Doppler Sidelobe Level Reduction

Nadav Neuberger,Risto Vehmas

doi:10.1109/lsp.2021.3067219

Abstract

Target masking due to high sidelobes in the range-Doppler domain is a common problem in radar signal processing. Masking occurs when there is large variation in targets' signal-to-noise-ratio levels, caused by differences in either range or radar cross section. In this letter, we consider the design of a waveform to reduce the masking of far range targets caused by near range targets. Our method is based on a time-frequency concatenation of a Costas sequence with shifted parts of itself. It allows the user to design a low sidelobe region in the range-Doppler domain. Moreover, it approximately preserves the desirable uniform sidelobe level and thumbtack behavior of the Costas ambiguity function. We demonstrate a 20 dB sidelobe level reduction within the desired region compared to a normal Costas code with the same bandwidth and pulse length.

Highlights

T HE ability of a radar system to estimate the range and Doppler of multiple targets heavily depends on the waveform of the transmitted signal
The range-Doppler (RD) response of the waveform is quantified by the ambiguity function (AF), which represents the theoretical matched filter (MF) output as a function of time delay and Doppler frequency
When multiple targets with different signal-to-noise ratio (SNR) levels are present, the MF sidelobes of a strong target may mask the response of a weaker target – preventing its detection

Summary

Introduction

T HE ability of a radar system to estimate the range and Doppler of multiple targets heavily depends on the waveform of the transmitted signal. The range-Doppler (RD) response of the waveform is quantified by the ambiguity function (AF), which represents the theoretical matched filter (MF) output as a function of time delay (range) and Doppler frequency (radial velocity). It encapsulates the detection performance, range and Doppler estimation accuracies and target resolution capability of the waveform. Depending on the operational scenario, target masking may be Manuscript received December 17, 2020; revised February 28, 2021; accepted March 12, 2021.

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