High linearity and wide-bandwith LFMCW generator for THz radar system

Bandwith and linearity directly determine range resolution of FMCW radar. In this paper, one way is proposed to generate high linearity and wide-bandwith LFMCW signal based on high speed DA convertor and FPGA, as a chirp generator for THz radar system. Because DDS can not acquire high output frequency, a modified module is presented called parallel DDS to produce high output frequency. Features of Linear Frequency Modulated Continuous Wave (LFMCW) signal and THz radar system are briefly illustrated. How to get amplitude data from parallel DDS quickly to send to high speed DAC is described. The block diagram, schematic of the chirp generator and parallel DDS structure are illustrated in detail. 400MHz spanning bandwith with central frequency in 1.5 GHz is acquired and sweeping time can be shorten to several us. Through THz radar Tx chain, 400 MHz bandwidth is 12 times multipled. The final transmitted bandwidth from THz radar is 4.8GHz, so the range resolution of 3.125cm can be achieved. Actually, the bandwidth of this LFMCW generator can be achieved to 800MHz At last, circuit board output signal is tested and signal purity, phase noise, linearity of this generator are showed and analyzed. At last the experiment of distance detection is also showed to prove this generator can be used in practical case.