Lumped-element equivalent circuit models for distributed microwave directional couplers

In this paper, we propose the lumped equivalent circuit models for the distributed coupled line directional and branch line directional couplers. Firstly, we have developed the conversion topologies from distributed microwave circuits to the lumped element circuits. Secondly, as applications of the proposed topologies, we have generated two 3 dB lumped-element directional couplers from their distributed versions. It was found that the derived S-parameters for the lumped-element couplers agree well with those of the corresponding distributed ones at the center frequency as well as within a certain bandwidth. This technology can be applied to construct highly integrated directional couplers in the WiFi/WiMAX RF applications in order to save valuable PCB space.