Development of Efficient Radar Pulse Compression Technique for Frequency Modulated Pulses

Abstract

Radar systems use Pulse Compression techniques to enhance the long range detection capability of long duration pulse and the range resolution capability of short pulse. Frequency and phase modulation techniques are used to increase the BW of long duration pulse to achieve better range resolution with limited peak power. Towards this purpose Linear FM chrip is the very common form of waveform. This waveform has a matched filtered Response (or ACF) with side lobe level is about -13dB. It may be improve by using methods such as windowing, adaptive filtering and optimization techniques. Windowing is used in LFM pulse Compression to reduce the side lobes. But the output SNR can be reduced by 1 to 2 dB due to windowing, this leads to reduce the false alarm rates in object detection applications. Using a train of stepped frequency pulses is an efficient method that achieves large overall Bandwidth and at the same time, maintains narrow instantaneous bandwidth. In this method a frequency step frequency step is added between successive pulses. One of the benefits of this method is that it allows us to use the duration between pulses to control the mid frequency of the other narrow band components of the radar system. Introducing frequency step between consecutive pulses is an efficient method to enhance the bandwidth of pulse train. The large value of frequency step gives large total bandwidth and better range resolution. However, if the product of frequency step and pulse width becomes more than one, the stepped frequency pulse-train ACF experiences unwanted peaks, referred to as “grating lobes”. A way to reduce these grating lobes is to use LFM pulses of some bandwidth B in place of the fixed frequency pulses. We can derive a relationship between frequency step, bandwidth and pulse duration such that nulls are placed at points where the grating lobes have been located by analyzing ambiguity function and ACF expression.