Wideband Doppler Radar Using a 18.5 GHz Microwave Direct Digital Synthesizer

This paper presents the design and realization of a Doppler radar system based on a direct digital synthesizer (DDS) operating at 18.5 GHz. The Doppler radar presented here relies directly on the signal generated by the DDS. This represents a major difference to other radar systems, where a DDS is used only for PLL stabilization of a VCO. The specification of the DDS as well as the design of the radar system will be presented here. First Doppler radar measurement results in the frequency band from 5-10GHz will be shown using a speaker membrane as a target oscillating with a frequency of up to 100Hz. The radar system shows excellent performance with a low noise floor and the ability to resolve small frequency differences down to 0.3 Hz. It is also demonstrated that the radar exhibits a perfectly linear ultra-wideband tuning characteristics, which eliminates the need for VCO tuning linearization.