6.1 INTRODUCTION

In this book we have reviewed two LPI radar signal waveforms, FMCW and phase-coded. The complexity of FMCW technology is minimal and it is very popular because of this reason. There are only two major obstacles that can be construed as a disadvantage in FMCW radars. These are the high time side lobes of the order of 13 dB down from the peak response and the nonlinearity in waveform generation for high bandwidths (and consequently high resolutions). The advantage of this waveform, however, lies in its Doppler tolerance, making it eminently suitable for use in aircraft target tracking radars. Phase-coded waveforms, on the other hand, are very easily adaptable to digital signal processing, being digital in nature, and polyphase codes produce relatively low time side lobes and as we have seen in some cases of polyphase codes, no time side lobes in the CW mode. The only problem is that these radars are relatively costly because of the complexity. The sub-pulse width defines the high range resolutions one can achieve using this waveform and unlike LFM waveforms, there are fewer constraints of nonlinearity in phase-coded waveform generation. The disadvantage with this waveform is that it has relatively poor Doppler tolerance against fast targets. We now study a third LPI waveform, which has found popularity in vehicular radars. This is the frequency hopped (FH) waveform. Generally, this class of signals transmits one frequency at each step. In doing this, it leaves the phase of the signal alone, that...