Design of Compact Filtering 180-Degree Hybrids With Arbitrary Power Division and Filtering Response

The design of filtering 180° hybrids with arbitrary power division and filtering response (filter order) is proposed in this paper. By integrating a 180° hybrid and bandpass filters into a single component, the overall circuit size can be reduced. The design theory based on the coupled resonator technique was detailed and validated experimentally through the fabrication of the third-order filtering 180° hybrid with a 0-dB power-dividing ratio and the second-order filtering 180° hybrid with a 6-dB power-dividing ratio. The power-dividing ratio can be arbitrarily determined through proper design of the coupling coefficients between the resonators. In addition, net-type resonators were selected to ensure compactness of the filtering 180° hybrids. The prototype sizes of the two example circuits were only approximately $0.25\lambda _{g} \times 0.12\lambda _{g}$ and $0.12\lambda _{g} \times 0.12\lambda _{g}$ , demonstrating highly compact circuit sizes. Moreover, isolations better than 30 and 21 dB within the operating passbands for the two circuits were achieved.