Amplitude-modulated continuous-wave radar in the terahertz range using lock-in phase measurement

Abstract

We present the principle and the experimental verification of a distance measurement method based on the propagation of terahertz waves. The method relies on modulating the amplitude of a resonant-tunneling-diode (RTD) oscillator used as terahertz-wave source and on measuring the phase of the detected wave by applying a quadrature mixing technique. The distance measurement is found to have a residual error as small as 0.063 mm (standard deviation), which is a record for an RTD-based terahertz-wave radar system. This is almost five times better than our previous record of 0.29 mm, when an oscilloscope was used for phase measurements; additionally, the quadrature mixing brings about numerous practical benefits, such as greatly reduced cost, size, weight, complexity, and power consumption.

Terahertz Emitter Using Resonant-Tunneling Diode and Applications

“…Through this operation, a low value of NEP (7.7 pW/Hz 1/2 ) has been obtained [51]. The application of RTD oscillators to THz radar has also been studied [43][44][45][46]. The THz radar has the advantage that it can be used in environments with poor visibility, due to the transparency of THz waves.…”

“…3D transparent imaging is also possible by combining THz radar and two-dimensional (2D) imaging systems. Figure 13 shows a simplified schematic diagram of a system and measurement results of THz radar using an RTD oscillator [43,44]. This system uses the amplitude-modulated continuous wave (AMCW) method.…”

“…The time of flight (ToF) of the THz wave from RTD to SBD is determined by the phase difference between the demodulated and reference signals, from which the distance to the object is obtained. THz radar system using RTD oscillator [43,44]: (a) Simplified schematic diagram of THz radar system using RTD oscillator with the amplitude-modulated continuous wave (AMCW)-SG: signal generator, and (b) error evaluated for the distance measurement with the AMCW using two modulation frequencies.…”

“…Currently, oscillation up to 1.98 THz has been obtained at room temperature [ 32 , 33 ], while structures for higher frequency and high output power are being studied [ 34 , 35 ]. Studies aiming toward several applications, such as imaging, spectroscopy, wireless communications, and radars, have recently begun [ 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 ]. In this paper, we review recent developments and applications of THz sources using RTD oscillators.…”

Subcarrier Frequency-Modulated Continuous-Wave Radar in the Terahertz Range Based on a Resonant-Tunneling-Diode Oscillator

“…In recent reports [12,13], we described a new terahertz-wave radar technique based on the principle of the amplitude-modulated continuous-wave (AMCW) radar, which we verified experimentally using an RTD oscillator as the terahertz-wave source. While that radar system is able to measure absolute distances with a precision below 100 µm by determining the phase of the modulation signal at two modulation frequencies, it has one particularly limiting disadvantage: it can only measure one distance at a time.…”