Four-port Spatiotemporally Modulated Circulator with Low Modulation Frequency

Abstract

Spatiotemporal modulation has gained significant attention recently for allowing the design of magnetless nonreciprocal components. However, most of the approaches presented to date require relatively large modulation frequencies, which creates significant challenges in their implementation at high frequencies. In this paper, we present a four-port magnetless circulator which overcomes this problem and works with a modulation frequency almost 100 times smaller than the operation frequency. The circuit is based on four Wheatstone bridges of varactors, connected to each other through inductors and modulated with a 90 deg phase difference, which, in addition to allowing operation with a low modulation frequency, is generally easier to realize than other phase differences. The design procedure of the proposed circuit is presented, together with simulation and measurement results, with a good agreement between them. For an operation frequency around 1 GHz and a modulation frequency of only 15 MHz, the proposed circulator can be designed to have high isolation (IX) (>30 dB) and relatively low insertion loss (IL) (<3 dB). The proposed approach can have important applications in high-frequency systems, where fast modulation is generally challenging.