Two-step windowing for both sidelobe suppression and SNR maximization of radar range profiles

A matched filter compresses wide chirps into narrow pulses to improve range resolution in radar imaging. The frequency response of the matched filter should be the conjugate spectrum of the chirp to maximize the signal-to-noise ratio (SNR) of the output. Usually, the chirp has a rectangle-like amplitude spectrum, and thus the matched filter should have a rectangle-like amplitude response. This, however, causes high sidelobes of the output. To suppress sidelobes, the amplitude response of the matched filter can be designed as a proper window. This, however, reduces the SNR because the amplitude response of the matched filter is not matched with the amplitude spectrum of the chirp any longer. This paper presents a novel scheme for both sidelobe suppression and SNR maximization. A proper window is selected to suppress sidelobes, but it is applied in two steps to maximize the SNR. First, the amplitude spectrum of the chirp transmitted by the radar is designed to be proportional to the square root of the window, and thus the amplitude spectrum of the chirp echoed from a scatterer is proportional to the square root of the window. Then, the amplitude response of the matched filter is also designed to be proportional to the square root of the window. Because the output of the matched filter to the chirp has an amplitude spectrum which is proportional to the window, the sidelobes of the output are suppressed. Besides, the SNR is maximized because the amplitude response of the matched filter is matched with the amplitude spectrum of the chirp. Simulated experiments confirm the effectiveness of this scheme.