Magnetic-free Circulator Based On Spatio-Temporal Modulation Implemented via Switched Capacitors for Full Duplex Communication

Conventional microwave circulators rely on ferro-magentic materials to break the time-reversal symmetry, and thus realizing a non-reciprocal passive device. In terms of system design, the use of ferromagentic materials renders the circulator integration with other transceiver blocks difficult, because they are still incompatible with CMOS fabrication processes. Recently, the concept of spatio-temporal modulation has been introduced to break the time-reversal symmetry, alleviating the need of ferromagnetic materials. In this paper, we present the design of a magnetic-less linear passive circulator based on spatio-temporal modulation of lumped first order LC resonators connected in a Y topology. Unlike other approaches, in this work the spatiotemporal modulation is implemented using switched capacitors, which yield a much simple circuit and has the advantage of high linearity. As a proof of concept, we designed a circulator at 1 GHz that shows an isolation of 44 dB with an insertion loss of 2.9 dB.