Integration Design of Passive Filtering Nonmagnetic Circulator Based on Spatiotemporal Modulation of Microstrip Filtering Delay Networks

A novel filtering nonmagnetic circulator based on the spatiotemporal modulation of microstrip filtering delay network using traditional PCB processing technology is presented in this article. By utilizing switches controlled by periodic signal to realize spatiotemporal modulation of microstrip filtering delay networks with large and flat in-band group delay response, the symmetry of time reversal is broken and thus the nonreciprocity characteristic is realized. By combining the advantages of both circulators and filters, a filtering nonmagnetic circulator is thus constructed. It is worth noting that all the circuit elements are fabricated using the traditional PCB technology, which is easy to integrate with other systems. The working mechanism is investigated theoretically and numerically. Moreover, the transmission characteristics and the group delay of the microstrip filtering delay network, which play a key role in spatiotemporal modulation in the proposed nonmagnetic circulator, are analyzed in detail. The prototype of the proposed filtering nonmagnetic circulator is designed, simulated, fabricated, and measured. The measured results agree well with the simulated ones. The nonmagnetic filtering circulator operates at 930–990 MHz with a relative bandwidth of 6.25%, and good filtering characteristics are also obtained. The maximum isolation of the circulator in the passband is better than −20 dB and the insertion loss (IL) is only 2.6 dB. Due to the compact microstrip filtering delay network with large group delay is used to realize the filtering and delay function in the system, good filtering characteristics are integrated into the nonmagnetic circulator, and the oversize is also reduced.