Microelectromechanical magnet-free non-reciprocal devices for in-band full-duplex applications

Abstract

In modern communication systems, the self-interference between the transmitter nodes and the receiver nodes is suppressed by either transmitting and receiving at different time slots (i.e., time division duplex) or at different frequency bands (i.e., frequency division duplex). Transmitting and receiving at the same time in the same frequency band (i.e., in-band full-duplex) can double the spectral efficiency directly at the physical layer of the RF front-end. The operation of full-duplex requires a circulator to suppress the self-interference between the transmitter and receiver. A circulator is a three-port non-reciprocal device that only allows the signal to transmit at one specific direction. Traditionally, Lorentz reciprocity is broken by applying magnetic bias to ferrite materials, therefore conventional circulators are bulky and expensive. In this dissertation, this problem is addressed by replacing the magnetic bias with periodic spatiotemporal modulation. High-Q MEMS resonators and MEMS filters are spatiotemporally modulated to break the time-reversal symmetry and reciprocity. Two different modulation schemes (angular momentum biasing and delay line based modulation) are discussed and developed, both demonstrating excellent performances in terms of insertion loss (IL), isolation (IX), return loss (RL), bandwidth (BW), linearity (in terms of P1dB and IIP3) and power consumption. Compared to the previous work based on the periodic modulation of either transmission lines (TLs) and lumped elements (LCs), the use of high-Q MEMS resonators and MEMS filters significantly reduces the modulation frequency. Besides ultra-low power consumption, the low modulation frequency prevents the leakage of the RF power into modulation paths and enables the use of RF switches with high power handling, therefore addresses such limitations associated with previous demonstrations on time-varying magnet-free circulators. Furthermore, other non-reciprocal devices based on similar spatiotemporal modulation methods are also summarized in this dissertation, including RF gyrator and RF isolator. With the developed non-reciprocal device, the full-duplex radio can be achieved without the need of bulky and expensive magnet devices.