Broadband Cyclic-Symmetric Magnetless Circulators and Theoretical Bounds on Their Bandwidth

In this paper, we explore theoretically and experimentally broadband spatiotemporally modulated magnetless circulators realized by combining three-port nonreciprocal junctions with three identical bandpass filters. We develop a rigorous theory for the proposed circuit, which allows optimizing its design and to derive a global bound on the maximum possible bandwidth (BW). We verify our theory with simulations and measurements of a printed circuit board prototype based on a differential wye junction and second-order Chebyshev bandpass filters, resulting in a measured fractional BW of 13.9% at a center frequency of 1 GHz.