Magnetic-free electrical circulator based on AlN MEMS filters and CMOS RF switches

This work reports the demonstration of a novel magnetic-free electrical circulator topology that facilitates the development of in-band full duplexers (IBFD) for simultaneous transmit and receive (STAR) RF applications. It uses CMOS-integrable components such as AlN MEMS filters (first-order in this work at 1.2 GHz) and CMOS RF switches, hence showing a compact approach that can be used in handheld devices. The linear time-invariant (LTI) AlN MEMS filter networks are parametrically modulated via a switching matrix to break its reciprocity. The modulation frequency and duty cycle were optimized so that the circulator can provide up to 15 dB of isolation over the filter bandwidth (2.2 MHz). The proposed prototype is a very compact solution for the implementation of magnetic-free circulators, which also intrinsically offers low noise and high linearity.