A 250GHz Autodyne FMCW Radar in 55nm BiCMOS with Micrometer Range Resolution

The increasing demands for compact, low-cost, and high-resolution radar systems have pushed the operation frequency to the terahertz range due to the shorter wavelength and larger available bandwidth [1–5]. However, the best-reported range resolution cannot go below 1.5mm with a 100GHz bandwidth [1], which is not enough for many industrial applications like small-defect detection and surface screening. Moreover, most previous works [3–5] are based on conventional transceiver architectures that use separate antennas for TX and RX or use parallel multi-antenna designs to increase the frequency bandwidth [1]. These structures not only increase the chip size but also degrade the radar performance when they are placed at the focal point of a collimating lens. This degradation occurs due to the separated antenna phase centers, which are not well located at the collimating lens focal point, causing a multi-beam radiation pattern. To overcome these challenges, we have adopted an autodyne FMCW radar structure [6, 7] with a phase processing method on the radar IF signal [7]. The autodyne is an oscillator that simultaneously carries out functions of generating the transmission and mixing the transmitted and reflected signals. There is no separate path for the RX signal in the autodyne, as the radiated and reflected signals exist at the same point of the autodyne circuit. Hence, it utilizes a combined antenna with a single-phase center for both transmitting and receiving parts. Besides, the phase processing method allows us to measure short ranges with an error no more than one-tenth of one-percent, which in terahertz frequencies provides micrometer resolutions [7]. Using these approaches, this paper demonstrates an autodyne FMCW radar with 66.7GHz bandwidth from 191GHz to 257.7GHz with a minimum range resolution of $54 \mu \mathrm{m}$. Across state-of-the-art, this design improves the range resolution by 28 times.