A 242-267 GHz Bistatic Superheterodyne Radar System for Precision Terahertz Sensing and Imaging in 65-nm CMOS

A state-of-the-art radar system suitable for terahertz (THz) sensing and imaging is presented. The system is composed of a bistatic superheterodyne transmitter-receiver (TX-RX) pair, designed and fabricated in a 65-nm CMOS process, driven by three coherent external sources and measured using a lock-in amplifier. The TX and RX chips each employ a wideband multiplier and amplifier chain to achieve a peak output radiated power of −2 dBm and a radar bandwidth of 25 GHz. A novel fully integrated dual-slot cavity backed antenna is designed based on characteristic mode analysis and coupled mode theory. The antenna achieves a 30 GHz wide gain, polarization and impedance bandwidth with front-side radiation and 18 dB polarization discrimination over the entire band. The three stage power amplifier (PA) is fed by a four-way slot-line-based balanced power divider. Miniaturization and symmetry enforcement are used to achieve 0.65 dB of insertion loss and less than 0.02° of phase imbalance over an ultra-wide bandwidth of 50 GHz centered at 125 GHz. For the RX, a two-stage superheterodyne architecture is used to improve the noise figure (NF), which is measured to be 15 dB at its minimum. The system architecture enables the entire wide-band scattering data of all targets to be downconverted onto a single continuous wave (CW) signal, whose amplitude and phase are measured with very high sensitivity and accuracy using a lock-in amplifier. The measured range and velocity accuracy are <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$40~\mu $ </tex-math></inline-formula>m and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$80~\mu $ </tex-math></inline-formula>m/s, respectively, which are shown to agree well with theoretical estimates. Finally, the system’s phase accuracy and long-term phase coherence are tested in a high-resolution inverse synthetic aperture radar (ISAR) experiment with several targets. The resulting images show a cross-range resolution that is at the theoretical diffraction limit (i.e., <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\approx }\lambda /2$ </tex-math></inline-formula>). To the best of our knowledge, this article reports the first coherent imaging radar system above 200 GHz in CMOS.