Design And Processing Of Hybrid Modulated HF Radar Waveform

Over-The-Horizon (OTH) HF radars work at heavily congested HF band. It is quite difficult to find broad clear frequency bands for system requirements. The randomly discontinuous spectra (RDS) signal is employed to combat spectrum congestion .However, the spectra discontinuity of the signal gets rise to high range sidelobes when matching the reflected echo, which is much more difficult for targets detection. So how to suppress the sidelobes of the randomly frequency-hopping signal is the key problem of this signal application.The directions of sidelobe suppression are two. On the one hand is the using of mismatch filters to suppress sidelobe; on the other hand, is to find the radar waveform with low sidelobes.There are three main indexes to measure the performance of the Sidelobe suppression filters. The three main indexes are: Peak Sidelobe Level, Integrated Sidelobe Level and Loss in Process Gain. They are defined as the ratio of the largest sidelobe power to peak response, the ratio of the total sidelobe power to peak response and the loss of signal to noise ratio caused by mismatch filter compared with the matched filter.The article first uses the method of mismatching signal processing technique on the basis of two-dimension signal processing scheme, using the Interactive Reweighed Least Square (IRLS) filter for suppressing the range sidelobes of randomly frequency-hopping signal. This sidelobe suppression filters are only designed to reduce the sidelobe to the level as low as possible, and the loss of Signal-to-Noise Ratio is not specially considered. In some cases, the Signal-to-Noise Ratio is large enough to influence the detection of signals.Against the loss of the SNR arose by mismatching (LPG: loss in process gain), the sidelobe suppression fillers with LPG arbitrarily given are proposed in this paper, and the design approach of optimal peak sidelobe level filler and optimal integrated sidelobe level filler with constant LPG is given. The non-linear constrained optimization theory is utilized to solve the problem and get the filter coefficients.Introduce the features of Phase-coded signal. The characteristics of Taylor Code and the P4 Code are analyzed in detailed. In order to improve the viability of the system, a new waveform which is called phase-coded modulated by frequency hopping signal (PCMFHS) is proposed. The design principles and thought of the PCMFHS are given. Signal processing principle and simulation result is discussed.