Broadband, Fast, and Linear Chirp Generation Based on DDS for FMCW Radar Applications

A broadband chirp generator for a linear frequency modulated continuous wave (FMCW) signal based on direct digital synthesis (DDS) is presented. This synthesized signal is used as the transmitting signal in an FMCW radar application for monitoring rapidly varying targets in short range. DDS technology is utilized in order to meet the requirements regarding temporal and spatial resolution of the system and to overcome deficiencies of conventional voltage controlled oscillator (VCO) technology. A method is presented in which the limited bandwidth of a commercial DDS chip is extended by a factor of four, resulting in an output signal bandwidth of more than 5 GHz and a chirp sweep time on the order of microseconds. The idea, the hardware setup of the frequency multiplier chain, and measurement results of the resulting chirp signal are presented. The results focus on the chirp linearity, the spectral purity, the output power level, as well as the dynamic range.