Magnet-less Circulator with Bulk Acoustic Wave Filter Delay Elements

Recent applications like quantum computing and in-band full duplex communication systems demand non-reciprocal components that are magnet-less, integrable, linear, and compact. This resulted in a lot of research interest in time variance based non-reciprocity. This paper reports the design and measurement of a four port non-reciprocal circulator using sequentially switched delay line (SSDL) elements. Bulk Acoustic Wave (BAW) filters are used as the time delay elements as they exhibit High-Quality factors, which resulted in a reduction in the modulation frequency compared to the previous LC demonstrations. The switching action of Single Pole Double Throw (SPDT) switches is synchronized with the delay of the BAW filters to route the electromagnetic signal to the desired port, without using a magnet. The commercial off-the-shelf BAW filters and SPDT switches are integrated on a Printed Circuit Board (PCB) and measured the S - parameter responses. The proposed circulator shows broad low insertion loss (IL) of 6 dB, and high isolation (IX) around 31 dB at 2.59 GHz with a BW of 60 MHz.