Digital tracking filter for FM-CW radar

摘要

The paper discusses a method for improving the SNR and hence sensitivity of Frequency Modulated Continuous Wave (FM-CW) radar. In FM-CW radar, a beat signal is generated internally, with its frequency proportional to the altitude. Beat frequency measurement results in error if the input has low Signal to Noise Ratio (SNR). SNR and hence sensitivity of the receiver can be improved using digital tracking filter. This can be achieved using a set of pre-designed band pass filters (BPF) or a suitable adaptive filter. In practical application, the statistical characteristics of signal and noise are usually unknown. The design of fixed filter is based on prior knowledge of both the signal and noise. Adaptive filters, on the other hand, have the ability to adjust their own parameters automatically and have immense potential in radar applications. The adaptive line enhancer (ALE) is applied before the FFT analysis to improve the detection performance. Performance of ALE using LMS, RLS algorithms and a set of block processing algorithms BLMS, BAP are compared. Adaptive filters with different algorithms were simulated in Visual DSP++ before implementing in hardware. The results show that ALE algorithms can be used as tracking filter for SNR enhancement. Processing speed of ALE algorithms were compared using Analog Devices Signal Processor 21060. Block LMS give better performance compared to other algorithms. Tracking filter using ALE BLMS was implemented in signal processing board. Results show that tracking filter using ALE improves the sensitivity of the system.