Magnet-less Circulators Based on Spatio-temporal Modulation of Bandstop Filters in a Delta Topology

摘要

In this paper, we discuss the design rationale and guidelines to buildmagnet-less circulators based on spatio-temporal modulation of resonantjunctions consisting of first-order bandstop filters connected in a deltatopology. Without modulation, the junction does not allow transmission betweenits ports, however, when the natural oscillation frequencies of the constituentLC filters are modulated in time with a suitable phase pattern, a syntheticangular-momentum bias can be effectively imparted to the junction and atransmission window opens at one of the output ports, thus realizing acirculator. We develop a rigorous small-signal linear model and find analyticalexpressions for the harmonic S-parameters of the proposed circuit, whichsignificantly facilitate the design process. We validate the theory withsimulations and further discuss the large signal response, including powerhandling and non-linearity, and the noise performance. Finally, we presentmeasured results with unprecedented performance in all metrics for a PCBprototype using a Rogers board and off-the-shelf discrete components.