Integrated Conductivity-Modulation-Based RF Magnetic-Free Nonreciprocal Components: Recent Results and Benchmarking

Achieving nonreciprocity and building nonreciprocal components through spatiotemporal modulation of material properties has attracted a lot of attention in the recent past as an alternative to the more traditional approach of exploiting Faraday rotation in magnetic materials. In this letter, we review recent research on spatiotemporal conductivity modulation, which enables low-loss, small-footprint, wide-bandwidth, and high-power-handling nonreciprocal components operating from radio frequencies to millimeter waves and integrated in a CMOS platform. Four generations of nonreciprocal circulators and circulator-based systems will be reviewed. We will also discuss metrics of performance that are important for wireless applications and standards, and introduce a new antenna (ANT) interface efficiency figure of merit (eta(ANT)) to enable a fair comparison between various types of antenna interfaces.