12.1 Principles of Phase Coding

The next two chapters elaborate on the two primary methods of obtaining range resolution by means of pulse compression. This chapter expands on phase coding of a single-frequency carrier, while Chap. 13 emphasizes pulse coding by shifting the carrier frequency during the waveform. Since the compressed pulse is generally the output of a matched filter, the properties of the output waveforms (in the absence of a Doppler shift) can be discussed in terms of the autocorrelation function of the transmit signal. When there is a Doppler shift, the complete ambiguity function must be discussed. The various forms of phase coding (or phase modulation) provide an excellent basis for general studies of signal processing and can provide for an intuitive grasp of the significance of the ambiguity diagram.

While many of the concepts in this chapter are also applicable to amplitude coding, the emphasis is on the transmission of a constant-amplitude sinusoidal carrier that is divided into N equal segments, each of duration ?. The majority of the material deals with binary phase (biphase) coding, for which the phase of the sine wave in each segment is set at either 0 or 180 from an arbitrary reference. This is expanded in Sec. 12.5 to include polyphase waveforms, in which each segment can have any one of M possible phases.

Phase coding can be further divided into two general classes depending on the duty cycle of the transmit...