Low-cost 3-D imaging recently becomes increasingly attractive because of its enormous potential in security applications. In particular, waves in the low terahertz (THz) range provide powerful capabilities for 3-D imaging due to the large available bandwidth and improved angular resolution (compared with radio frequency and mm-wave signals), and good transmission (<0.01 dB/m) through extreme weather conditions (compared with infrared and visible light).
We propose a comb radar architecture to increase the bandwidth to more than 0.1 THz without using ultra-wideband components. It utilizes equally-spaced signal tones with frequency modulation; the generated IF signals are then combined in the digital domain. The proposed comb radar architecture has many advantages compared with conventional Frequency-Modulated Continuous-Wave (FMCW) radar in silicon: peak performance is maintained across a large bandwidth, finer Doppler frequency resolution, larger intermediate frequency (thus smaller flicker noise) and higher linearity. Similar to our previous frequency-comb-based THz spectrometer, in this radar, all components including antennas can be integrated on a single chip, our solution has merits of low cost small volume, and lightweight.
We show the architecture of the proposed comb radar. It consists of multiple channels with a suitable bandwidth in each channel, leading to an aggregated bandwidth that is larger than 0.1 THz. Note that the number of channels is not limited by the architecture, so the aggregated bandwidth is only limited by the bandwidth of a single channel. The FMCW signal is fed into the first channel directly and up-converted through single sideband mixers to the subsequence channels step by step. The transmitter and the receiver share one on-chip antenna to save the area and power. The mixer first receiver utilizes the transmit power as local oscillator signal and down-converts the received echo signal to IF for further image processing. In addition, since backside radiation has asymmetric radiation pattern and multiple reflections in the attached silicon lens, front- side radiation is desired. To this end, we adopt a substrate-integrated-waveguide antenna utilizing its multiple high-order resonance modes in orthogonal directions. Compared with patch antenna, the new on- chip antenna design has much wider bandwidth (>10% fractional bandwidth).