5.1 INTRODUCTION

In the last chapter, we had examined the performance and design aspects of frequency modulated CW signals, the so-called FMCW signal. This signal has found wide application in LPI radars. In this chapter, we shall, investigate the design and performance of phase-coded signals that have also found popularity in LPI radar waveform compression design. In the class of phase-coded signals, there is a wide variety. This class of signals transmits at one frequency, but changes the phase as it transmits in a predetermined order. This is the exact reverse concept as compared to frequency-coded signals that will be studied in Chapter 6, wherein the phase is kept constant and the frequency is varied at each discrete step. Usually, this class comprises codes like Barker, Frank, complementary pairs or P1, P2, P3, and P4 codes. Barker codes fall into a class called binary phase codes, in that they can take only one of two phase values, zero, or one. Frank code and codes like P1 through P4 fall into a class called polyphase codes, in that they can take values other than one. There are also a class of codes called polytime codes T1, T2, T3, and T4 [1]. These code sequences use fixed phase states with varying time periods at each phase state. Due to lack of space we cannot examine polytime codes. The reader is referred to [1] for information on polytime codes and the references listed therein. We shall examine for each...