Title: Improvement in the Operating Bandwidth of Coplanar Waveguide Circulator
Abstract: CPW circulator is highly compatible with microwave integrated circuits. CPW circulator, however, has an inherent drawback in that the ground conductors are inevitably disconnected by the Y-shaped configuration of the junction. Therefore, the operation characteristics of the CPW circulator have been inferior to those of other circulators. In this paper, a three-legged top plate conductor covering over the ferrite disk like an air bridge is proposed to improve the operation characteristics. With this scheme the ground conductors are tightly connected with one another, and the ferrite disk can be better coupled with the magnetic field outside. The CPW circulators with the top plate were manufactured and their performances measured. As a result, we obtained an isolation ratio of more than 20dB, an insertion loss of less than 1dB, and a bandwidth of greater than 250MHz each at 11GHz, performances that compare favorably with those of conventional CPW circulators.