Abstract
Many applications in radar systems require low range side-lobe performance which is achieved by pulse compression processing. Most used chirp signal for this processing is linear frequency modulation (LFM) signal but with a presence of first high side-lobe level. Suppression of this side-lobe requires weighting function causing the reduction in signal to noise ratio at the receiver owing to mismatch loss. Non-linear chirp signals are introduced as a solution and became most practiced signals aimed at reducing side-lobes. In this paper, an overall piece wise non-linear frequency modulation chirp signal is designed by merging two stages, one with linear function and the other with a tangent based non-linear function. Simulation results show significant reduction in the sidelobe level of autocorrelation function when NLFM is generated in this method.
Highlights
Pulse compression is a favorable technique which influences target parameter estimates by employing different signal models such as Frequency modulation (FM) and Phase modulation (PM) [1, 2]
This paper mainly focuses on Non-linear Frequency Modulation (NLFM) signal design by fusing piecewise Linear Frequency Modulated (LFM) and NLFM functions and the resultant function is capable of generating an overall NLFM waveform
The chirp signal of the new NLFM signal and instantaneous frequency variation for different values of α1 are shown in fig 4 and fig 5 for the total duration of τ=10μs(1e7s) and bandwidth β=20MHz(2e7Hz) and the autocorrelation function which is nothing but the matched filter output for different values of α1 is shown in fig 6
Summary
Pulse compression is a favorable technique which influences target parameter estimates by employing different signal models such as Frequency modulation (FM) and Phase modulation (PM) [1, 2]. Since 1940s Linear Frequency Modulated (LFM) signal is the most used pulse compression waveform as it can be generated and bandwidth can be effectively used as the frequency is linearly swept over to cover the entire signal bandwidth. NLFM signals have a vast applicability in radar systems with a good range resolution, good interference mitigation, better signal to noise ratio (SNR), low-cost, and has a spectral weighting function inherently in their modulation function which effectively which gives a pure matched filter output with low side-lobe levels [7, 8]. In the first part of the paper two-stage LFM signal design is described and later the new NLFM signal design methodology is discussed
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