Synthesis of a class of quadrature circuits based on coupled-resonators

This paper presents a technique for the synthesis of hybrid couplers based on coupled resonators. All these circuits are, in general, based on several quarter-wavelength transmission lines and preserve a 90° phase shift among the outputs. The coupled-resonator structure, instead, introduces a selective response that can be controlled in order to obtain filtering functions. This property is seen to be an advantage because a single device can act both as a coupler as well as a filter, leading to a significant mass and footprint saving.