18.1 A W-Band Transceiver Array with 2.4GHz LO Synchronization Enabling Full Scalability for FMCW Radar

Closing the angular resolution gap between CMOS radar and optical imaging systems can enable an entirely new cost-effective radar-centric perception solution, but requires extremely large transceiver (TRX) arrays to achieve LiDAR-like angular resolution. Multi-chip cascading of mm-wave radars [1–3] has become the norm to enable these large TRX arrays, but the size of these arrays is still limited due to challenges in achieving low-cost signal distribution across a large aperture. Today, multi-chip radar cascading solutions use mm-wave LO frequencies (20GHz [1], [2], 40GHz [3]) along with on-chip frequency multipliers with modest multiplication factors (×4 [1], [2], ×2 [3]). However, operating at these frequencies is cost-prohibitive and severely limits the size of the array [1]. For example, for a 64-TX and 64-RX array, the calculated path loss on a Rogers 3003 substrate in an H-tree distribution network reaches 87dB at 40GHz, which requires more than 70 amplifiers with 15dBm output power and 25dB gain alongside the distribution network to compensate the loss. Moreover, maintaining phase coherency required for FMCW systems is also infeasible for such amplifier implementations. Thus, enabling truly scalable TRX arrays requires signal distribution at much lower LO frequencies, which introduces fundamental performance challenges.