Multi-beam, Scalable 28 GHz Relay Array with Frequency and Spatial Division Multiple Access Using Passive, High-Order N-Path Filters

P. P. Khial, S. Nooshabadi, A. Fikes, A. Hajimiri

A 28 GHz scalable relay array that independently re-routes multiple beamformed data-channels in different frequency bands is presented, allowing for frequency and spatial division multiple access. The array is implemented at the element-level with a 65 nm CMOS RFIC that has two transmit-and-receive branches. Each transmit-and-receive branch provides phase delay, true time delay, and amplitude control for up to 3 frequency channels independently and simultaneously. The baseband signal chain is enabled by a dual function N-path filter architecture that is passive and inductorless yet provides high-order filtering with complex roll-off and performs phase shifting. The resulting array consists of a 2-chip, 4-branch prototype that independently steers 3 frequency multiplexed incident data beams into different spatial directions, with true time delay control in each beam. A radiative measurement shows the router supporting a simultaneous throughput of 625 Mb/s 32-QAM data across 3 frequency channels that are independently spatially steered.