The chip-cascading solution has been widely used in millimeter-wave (mm-wave) frequency-modulated continuous wave (FMCW) radars to enable large-aperture arrays in multiple-input and multiple-output (MIMO) operations. However, scalability remains problematic during implementation. In this work, we propose a W-band FMCW radar transceiver chip architecture to enable full scalability by adopting an local oscillator (LO) distribution frequency as low as 2.4 GHz for cross-chip synchronization. Implemented in the 40-nm CMOS process, we demonstrate a four-channel receiver chip and a single-channel transmitter chip that can operate from 80 to 90 GHz. Meanwhile, we use a ceramic interposer with integrated patch antennas to package the chips to achieve antenna-in-package (AiP). To reconstruct the 84-GHz FMCW chirp signal from the off-chip 2.4-GHz LO distribution chain, we design an on-chip injection-locking-based x 35 frequency multiplier, while the phase noise and harmonic spur issues during reconstruction have been analyzed and carefully arranged. The measured phase noise and harmonic rejection ratio (HRR) are - 112 dBc/Hz at 1-MHz offset and above 50 dBc, respectively, allowing for an over 100-dB radar dynamic range. We demonstrate a radar system by cascading two receiver chips and two transmitter chips to enable an 8 x 2 MIMO array, and achieve an 11.3 degrees angular resolution through an outdoor experiment. Prototype radar systems enable for advanced chip cascading, which is beneficial for next-generation scalable high-resolution imaging radars.
