Pseudorandom Code Waveform Design for CW Radar

Certain surveillance radar applications require that the transmitted signal be continuous wave (CW) and wide bandwidth to meet range and range-rate resolution, and also performance requirements in clutter, multiple targets, or other interfering environments. Although an unmodulated CW radar is well suited for making range-rate (Doppler) measurements, a modulation of the transmitted signal is generally required to make range measurements. We describe the use of a pseudorandom code (PRC) which modulates the radar transmitter carrier to meet the range resolution and measurement requirements. The tradeoffs for selecting the PRC code parameters are presented together with a functional description. It is shown that in order to achieve the desired performance, it is necessary that Doppler ambiguities be avoided. This generally causes the range measurement to be ambiguous. The range ambiguity can be removed by staggering the code clock frequency during the time on target. Special emphasis is placed on an algorithm which allows range measurements to be made to an accuracy of one code bit.