Software-Defined Six-Port Radar Technique for Precision Range Measurements

A software-defined radar measurement system on the basis of a six-port receiver technique is proposed and described in this paper. The system makes use of a hybrid scheme of two performance-complementary operating modes, namely, frequency-modulated continuous-wave (FMCW) and two-tone continuous-wave signals. Generally, the FMCW-based measurement technique is deployed to give an approximate range value of target while the two-tone continuous-wave (CW)-based measurement technique can accurately determine the range that may, however, be ambiguous. The six-port circuit is used for the receiver as a precision phase detector in two-tone CW function and at the same time as a mixer in FMCW function. Various waveforms are generated in direct digital synthesizers and processed by different algorithms in a digital signal processor. The switching between the frequency-modulated CW and two-tone CW functions is controlled by software to improve the resolution and ensure a reliable operation. A system prototype is designed and made for a C-band demonstration. The Schottky diodes used as power detectors in the six-port are calibrated so that they can be used beyond the square-law region, thus allowing a higher power level and a better dynamic range. Measured results validate the proposed software-defined platform and accurate range results are confirmed.