Quad-Junction Self-Biased Circulator with Wide Operational Bandwidth

The choice of hexaferrites has always been crucial in the design of self-biased circulators, as it directly affects the device's performance. The available hexaferrite materials are only suitable for operation in high-frequency bands. At low frequencies, they often cause high insertion loss (IL) and limited bandwidth. This paper introduces a novel approach to the design of self-biased circulators. Parallel connection of two hexaferrite junctions with opposite directions of internal magnetic bias achieves a fractional bandwidth (FBW) of 3.67% for self-biased circulators operating in the C-band. This FBW is 2.5 times the traditional single-junction self-biased circulators. The self-biased circulator presented in this paper, operating in the frequency range of 5.35-5.55GHz, exhibits return loss (RL) and isolation both exceeding 20dB, with insertion loss below 1dB over 50% of the operational bandwidth.