Radio Frequency Magnet-free Circulators Based on Spatiotemporal Modulation of Surface Acoustic Wave Filters

TL;DR

This paper introduces a compact, high-performance, magnet-free RF circulator using spatiotemporal modulation of surface acoustic wave filters, enabling efficient full-duplex communication without bulky magnetic components.

Contribution

It presents a novel SAW filter-based circulator with reduced modulation frequency, low power consumption, high linearity, and a new quad configuration for increased bandwidth.

Findings

Achieved broad bandwidth and high isolation on a chip scale.

Reduced modulation frequency by at least 20 times compared to previous works.

Demonstrated low-loss, high-Q SAW filter-based non-reciprocal band.

Abstract

In this paper, a new generation of magnet-free circulators with high performance is proposed. Circulators are crucial devices in modern communication systems due to their ability to enable full-duplexing and double the spectral efficiency directly in the physical layer of the radio-frequency (RF) front-end. Traditionally, Lorentz reciprocity is broken by applying magnetic bias to ferrite materials, therefore conventional circulators are bulky and expensive. In this paper, this problem is addressed by replacing the magnetic bias with periodic spatiotemporal modulation. Compared to previous works, the proposed circulator is constructed using surface acoustic wave (SAW) filters instead of transmission lines (TL), which reduces the modulation frequency by at least a factor of 20 and ensures ultra-low power consumption and high linearity. The miniaturized high quality (Q) factor SAW filters also lead to a low-loss non-reciprocal band with strong isolation (IX) and broad bandwidth (BW) on a chip scale, therefore addressing such limitations in previous magnet-free demonstrations. Furthermore, compared to the conventional differential circuit configuration, a novel quad configuration is developed, which doubles the intermodulation-free bandwidth.