Three-dimensional terahertz imaging using an amplitude-modulated resonant-tunneling-diode oscillator

We report on a three-dimensional imaging system obtained by combining an amplitude-modulated continuous-wave (AMCW) radar with two-dimensional mechanical scanning. The system is based on a resonant-tunneling-diode (RTD) oscillator emitting at 660 GHz and modulated at 4.5 GHz. The axial distance measurement relies on determining the phase of the demodulated signal by means of an IQ mixer. With careful calibration, the distance measurement error was reduced to 20 µm.