A Magnetic-Free RF Circulator Based on Spatiotemporal Modulated LN/SiO₂/Sapphire Surface Acoustic Wave Delay Lines

In this study, we explore the design and implementation of a magnetic-free radio frequency (RF) circulator using spatiotemporal modulated thin film surface acoustic wave delay lines. The four-port circulator is designed based on two tightly packed low-propagation loss acoustic delay lines (ADLs) on a single LN/SiO2/sapphire (LNOS) chip with sequentially-switched delay line (SSDL) topology, complemented by two external switch modules composed of commercially available RF switches. The ADLs are characterized by a low insertion loss (IL) of 5.54 dB, a wide 3-dB bandwidth of 5.45%, and a large group delay of 110 ns at 880 MHz, operating in shear horizontal (SH) mode. The implemented circulator achieves a nonreciprocal contrast of 18.2 dB and 20.8 dB between IL of 10.8 dB and isolation of 29 dB (port 3 to port 1) and 31.6 dB (port 4 to port 1) over an isolation bandwidth of 6% (53.6 MHz), with a low modulation frequency of 2.27 MHz.