Ultra-Low Sidelobe Nonlinear Frequency Modulated Waveform based on Inverse Error Function

초록

An inverse error function (IERF)-based nonlinear frequency modulated (NLFM) signal is investigated for pulse compression with a very low sidelobe level (SLL) and efficient use of the frequency spectrum. With a time-bandwidth product (TBP) of 200 and a pulse width of 60 μs, a simple IERF-based NLFM signal produces a correlation result with a peak sidelobe ratio (PSLR) of −46.14 dB and an integrated sidelobe ratio (ISLR) of −31.25 dB. However, these PSLR and ISLR values are still not suitable for weather radars and imaging radars. Additionally, there is a problem of Tx energy leaks outside the bandwidth, which could interfere with radars operating in adjacent bands. To address these issues, a modified IERF combining a pulse shaping function of raised cosine is proposed. A parameter study is performed, and hybrid optimization combining genetic algorithm and Nelder-Mead search is used to find the optimal solution. With this approach, even without amplitude windowing, a PSLR of −97.23 dB and a one-sided occupied spectrum bandwidth of only 20.07 MHz based on the cutline of −90 dB attenuation. In addition, excellent Doppler tolerance was observed with a reduced correlation peak of only 0.35 dB and a 2.24 dB increase in PSLR.

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