This chapter has presented the basis of a continuous nonlinear FM waveform design capable of achieving range sidelobe levels of better than -70 dB, suitable for use with a satellite-borne precipitation radar. The waveform shows good Doppler tolerance, with the low sidelobe performance maintained over the full Doppler bandwidth associated with the antenna footprint. A clear-cut waveform design procedure has been presented that does not require the implementation of numerical optimization procedures. It has been shown that slowly varying phase and amplitude errors in the transmitter and receiver have relatively little effect, but rapidly-varying errors result in paired echo sidelobes whose level can be significant. A closed-loop calibration process is therefore essential to remove the effects of errors in the analog portions of the transmitter and receiver. Reference to the original problem (Figure 1) shows that in fact it is only necessary to have low range sidelobes on one side of the radar point target response. There may therefore be scope in designing a waveform to exploit this, trading sidelobe energy from one side of the response to the other. Some early work on this problem has shown promise [7]. In the context of waveform diversity, the work described in this chapter is an example of an application that demands the generation and processing of very precise waveforms, which is only now becoming practical with high-speed digital circuits with large number of bits. More generally, pulse compression processing giving low range sidelobe performance is required in a number of applications in modern radar systems, so these ideas will find wider application than just meteorological radar. In future years it may be expected that interface between analog and digital parts of a radar will migrate further and further towards the antenna, so techniques of this kind will become easier.

Inspec keywords: spaceborne radar; FM radar; radar receivers; numerical analysis; optimisation; radar transmitters; calibration; meteorological radar

Other keywords: radar systems; transmitter; antenna footprint; clear-cut waveform design procedure; closed-loop calibration process; radar point target response; numerical optimization procedures; waveform diversity; receiver; continuous nonlinear FM waveform design; pulse compression processing; Doppler bandwidth; satellite-borne precipitation radar; Doppler tolerance; meteorological radar

Subjects: Radar equipment, systems and applications; Other numerical methods; Optimisation techniques