Broadband Cyclic-Symmetric Magnet-less Circulators and Theoretical Bounds on their Bandwidth

TL;DR

This paper presents a theoretical and experimental study of broadband magnet-less circulators using spatiotemporal modulation, deriving bounds on their bandwidth and demonstrating a prototype with nearly 14% fractional bandwidth at 1 GHz.

Contribution

It introduces a rigorous theory for broadband cyclic-symmetric magnet-less circulators and establishes a fundamental bandwidth limit, validated through simulations and experimental measurements.

Findings

Achieved a measured fractional bandwidth of 13.9% at 1 GHz.

Developed a global bound on the maximum bandwidth for these circulators.

Validated the theory with a PCB prototype based on a differential wye junction.

Abstract

In this paper, we explore theoretically and experimentally broadband spatiotemporally modulated (STM) magnet-less circulators realized by combining three-port non-reciprocal junctions with three identical bandpass filters. We develop a rigorous theory for the proposed circuit, which allows to optimize their design and to derive a global bound on the maximum possible bandwidth (BW) for cyclic-symmetric magnetless circulators. We verify our theory with simulations and measurements of a printed circuit board (PCB) 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.