Distance measurement using a subcarrier frequency-modulated continuous-wave radar based on a resonant-tunneling-diode oscillator

We have previously introduced a new principle for distance measurement using terahertz waves, similar to the frequency-modulated continuous-wave (FMCW) radar, but where the sawtooth frequency modulation is applied to an amplitude modulation subcarrier of the terahertz wave instead of the carrier itself. The method is particularly useful when the terahertz-wave source is a resonant-tunneling-diode (RTD) oscillator, which can be more reliably modulated in amplitude than in frequency. This report describes using the new principle in a typical radar configuration as well as ways of achieving a better accuracy.