Quasi‐optimal Rat‐Race Coupler Design With Arbitrary Port Impedance

ABSTRACT This paper presents a novel design method of quasi‐optimal rat‐race coupler with arbitrary port impedance. The arbitrariness of the port impedance is fully considered in the design of the rat‐race coupler, which can avoid the additional configuration of matching network when connecting with other components. An integrated design equation for the rat‐race coupler is derived using the even–odd mode method. Combined with the quasi‐optimal theory, the dual‐band, broadband, and compact design methods of arbitrary port impedance rat‐race coupler are proposed, and the different characteristics can be achieved by only adjusting the parameters without any structure change. Three rat‐race couplers are fabricated using double‐sided parallel‐strip line (DSPSL) for experimental verification, and the results are in great agreement with the theory.