Fast and Accurate THz Permittivity Measurement Using a Self-Heterodyne Technique and Multitone Signal with Nonuniform Intervals

A permittivity measurement system operating in the terahertz waveband around 300 GHz achieves fast measurement by using a self-heterodyne technique to measure phase differences. Errors are reduced because a multitone technique with nonuniform frequency intervals enables us to apply a phase-unwrapping method to the self-heterodyne system. For multitone signal generation, just single-frequency oscillators and local oscillator leakage from a modulator are used. The system achieves a measurement time of 0.03 ms at one point, which is 1/200 compared to a conventional system using a vector network analyzer. With the same measurement time, the maximum measurement error can be reduced to less than half compared to the conventional two-tone self-heterodyne system.