Phase-Coded Stepped Frequency Linear Frequency Modulated Waveform Synthesis Technique for Low Altitude Ultra-Wideband Synthetic Aperture Radar

This paper discusses a new waveform synthesis technique particularly suitable for low altitude ultra-wideband (UWB) synthetic aperture radar (SAR) systems. The proposed technique synthesizes a phase coded UWB chirp by transmitting a burst of coherent phase-coded sub-band chirp pulses and combining the collected echoes using a special digital signal processing (DSP) algorithm. A lab prototype is built for the feasibility study and validation of the proposed technique. From the results, it is clearly shown that 1) the proposed technique can synthesize UWB chirp pulses; 2) the proposed DSP algorithm can combine the collected sub-band echoes into an echo of a wider bandwidth; and 3) the proposed technique can improve the range resolution of the SAR system without altering much of its system design. The main advantage of the proposed technique is that it can improve the range resolution of an existing SAR system without the need to increase the baseband bandwidth of the system.