ContinuousWave Signals

Continuous wave (CW) radar is one of the earliest forms of radar. It is found today mostly in short range radar applications such as proximity fuzes, radar altimeters, atmospheric probing, ground penetrating radar and automotive applications. The CW signal is also useful in velocity measuring radars such as airborne Doppler navigation radars, artillery muzzle velocity and police radars. In military applications CW waveforms are sometimes referred to as ?>low probability of intercept?> (LPI) waveforms, because of their low peak power.

This chapter discusses many modulation waveforms of the CW signal. Modulation increases bandwidth which is inversely related to the range resolution. The periodic ambiguity function (PAF) is a natural tool to describe the delay-Doppler response of CW periodic signal, and it is revisited in this chapter.

An important family of modulation waveforms are periodic phase codes with ideal periodic autocorrelation (PACF). They all yield PACF with zero delay sidelobes. Examples reconsidered here are P4, Frank and Golomb bi-phase.

Frequency modulation is also found in CW radars. These waveforms do not yield zero delay sidelobes, but with proper weighting (on receive) the sidelobes can be reduced. Among the frequency modulations discussed are: sawtooth, sinusoidal and triangular waveforms. Methods to control the delay peak response by utilizing harmonics of the periodic modulation are described.

Simple implementation of CW radar receiver is described. It is based on mixing the received delayed return with the original transmitted signal. This kind of processing belongs to the family of stretch processors discussed in an earlier chapter.