Radar System Studies Using Simulation Techniques

Abstract

<p>Pulse-compression is a technique used in radar to transmit a long pulse while retaining the range resolution of a short pulse. The echo from the target is compressed in the matched filter of the radar receiver and the range resolution becomes equal to the width of the central peak of the autocorrelation function of the transmitted signal. A range tracking loop and a range surveillance moving target indicator (MTI) radar using pulse-compression techniques are studied in this thesis. The antenna of these systems is assumed to point along a constant azimuth to simplify the radar surroundings so that the nonlinear aspects of the circuits may be investigated.</p> <p>In a range tracking loop the nonlinearity arises in the delay error feedback process, while in an MTI radar it arises through the limited dynamic range of the circuits used. This thesis presents a computer simulation study of these nonlinear radar systems using Monte Carlo techniques. The computer used in the study is of an interactive kind with oscilloscope display.</p> <p>A new range tracking loop referred to as the decision-directed delay-lock loop has been developed using the fast Fourier transform (FFT) for cross-correlation with a stored replica of the transmitted signal. The loop uses all the lagged products of the FFT cross-correlation output, ans is shown to have a wide dynamic range for large steps of input delay. Using signals already available in the loop, additional features such as automatic feedback gain control and a mechanism for detection of unlocking are built into the loop.</p> <p>The MTI pulse-compression radar has been investigated to determined the effect of a linear-limiting intermediate frequency (IF) amplifier on the signal-to-noise ratio (SNR) at the MTI output. For this study the FFT was used for the purpose of matched filtering and for generating various types of coherent clutter. It has been shown that large SNR losses due to the time-varying effective gain of the clutter-captured limiter may occur at some ranges with particular types of clutter spatial distributions.</p>