Page 310 - Fundamentals of Radar Signal Processing

TABLE 4.2 Sample Minimum Peak Sidelobe Biphase Codes

4.10.2 Polyphase Codes
Biphase codes, as noted previously, have poor Doppler tolerance. They also
suffer from precompression bandlimiting effects. As is shown in Fig. 4.51, the
spectrum of a typical biphase code not only exhibits the desired mainlobe
spreading, but also a very slow falloff of the far sidelobes. This is a direct

consequence of the sharp phase discontinuities. Practical receivers will have a
noise-limiting bandpass filter that will bandlimit the biphase waveform
spectrum, smoothing the phase transitions. This has the effect of mismatching the
received waveform relative to the correlator, reducing the peak gain and
widening the mainlobe.

FIGURE 4.51 Matched filter output for a 16-bit Frank code.