Magnet-Free Circulator Using BAW Filters Based on Spatiotemporal Modulation for Full-Duplex Applications

This paper presents the design and measurement of a magnet-free circulator based on bulk acoustic wave (BAW) filters, employing spatiotemporal modulation techniques for full-duplex communication systems. BAW filters are recognized for their high-quality factors, which allow for a reduced modulation frequency compared to previous LC implementations. The appropriate modulation frequency and amplitude facilitate the routing of electromagnetic signals to the desired port without using a magnet. Simulations were conducted using the Advanced Design System (ADS). Commercial off-the-shelf BAW filters and varactors were integrated onto a Rogers RT/duroid 5880 substrate. The measured results of the proposed circulator indicate an insertion loss (IL) of 9 dB, isolation of 18 dB from port 1 to port 3, a 15 dB isolation bandwidth (IX-BW) of 8 MHz, and a return loss (RL) of approximately 33 dB at 2.5 GHz with 19 MHz sinusoidal modulation signals.