Magnetic-Free Radio Frequency Circulators Using Bulk Acoustic Wave Filters

Communication systems require efficient nonreciprocal circulators, but traditional methods using external magnetic fields are bulky, expensive, and not CMOS-compatible. Recent research has demonstrated alternative approaches using coupled LC resonators with spatio-temporal modulation, providing strong nonreciprocity with reasonable loss and bandwidth. However, it requires a large area. This letter proposes a compact solution using three identical bulk acoustic wave (BAW) filters in a wye configuration. The BAW circulator demonstrates efficient nonreciprocal signal flow in a compact size, shrinking the need area to 16%, making it suitable for future communication systems. Our findings also include that BAW filters offer a smaller footprint, low loss, and high noise rejection. Modulated by varactors with a phase difference of 120 °, the BAW filters provide 15 dB isolation by rotating the RF signal. We showcase a 3.5 GHz BAW circulator achieving 15 dB isolation with a 17.5 dBm modulation at 35 MHz, offering a wider bandwidth than reference designs. Further optimization and integration of BAW circulators hold promise in advancing miniaturization and efficiency in communication systems.