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

Abstract

We introduce a new principle for distance measurement in the terahertz-wave range using a resonant-tunneling-diode (RTD) oscillator as a source at 511 GHz and relying on the frequency-modulated continuous-wave (FMCW) radar technique. Unlike the usual FMCW radar, where the sawtooth frequency modulation is applied to the carrier, we propose applying it to a subcarrier obtained by amplitude modulation; this is advantageous when the source cannot be controlled precisely in oscillation frequency, but can easily be modulated in amplitude, as is the case of the RTD oscillator. The detailed principle and a series of proof-of-concept experimental results are presented.

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.…”

“…Basic research into various applications of RTD oscillators has begun, including for imaging [ 36 ], sensors [ 37 ], linear encoders [ 38 ], communication [ 39 , 40 , 41 , 42 , 50 ], and radars [ 43 , 44 , 45 , 46 ], in addition to spectroscopy [ 47 ] shown in the previous section. It is a future task to develop various applications of RTD oscillators.…”

“…The subcarrier modulation method can be extended to other radar systems, such as the frequency-modulated continuous wave (FMCW) radar. A subcarrier FMCW radar using an RTD oscillator and a preliminary experiment for the distance measurement of two targets have been reported [ 45 ].…”

“…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.…”

Discrete Fourier Transform Radar in the Terahertz-Wave Range Based on a Resonant-Tunneling-Diode Oscillator

“…Initially, the positions and shapes of targets in the propagation direction were determined exclusively by using the time-domain spectroscopy, a time-of-flight technique whereby the arrival time of terahertz radiation pulses was used to measure propagation distances. Other ranging techniques now use the frequency-modulated continuous-wave (FMCW) radar principle [ 1 , 2 , 3 , 4 ], the amplitude-modulated continuous-wave (AMCW) radar principle [ 5 , 6 ], interferometry [ 7 ], or computed tomography [ 8 ]. In recent years, a new technique has been added to the arsenal of terahertz-wave ranging: the optical coherence tomography (OCT), either in its original form, the time-domain (TD) OCT, in which a low-coherence (wide-spectrum) light source is used [ 9 ], or the source-swept (SS) OCT, relying on a tunable monochromatic source [ 10 , 11 , 12 ].…”