Millimeter-wave full-duplex wireless: Applications, antenna interfaces and systems

Millimeter-waves offer significantly wider channel bandwidths (BW) than RF and are drawing significant interest for short-range wireless personal area networks (WPANs), vehicular radar and next generation (5G) cellular communication. Full-duplex is another emergent technology which can theoretically double the data capacity by transmitting and receiving simultaneously on the same frequency. This paper reviews recent developments at Columbia University on millimeter-wave full-duplex which merges these two emergent technologies. In this context, potential applications for millimeter-wave full-duplex links are described. A 60GHz full-duplex transceiver and 25GHz magnetic-free non-reciprocal passive circulator implemented in 45nm SOI CMOS are discussed. The 60GHz full-duplex transceiver employs polarization-based antenna and RF cancellation to achieve almost 80dB self-interference (SI) suppression. The 25GHz circulator is based on spatio-temporal conductivity modulation and achieves 3.2dB insertion loss, >18.3dB isolation (limited by the measurement setup) over a 4.6GHz 1dB insertion loss (IL) BW, and an input P1dB of >20dBm. Finally, topics for future research are discussed.