Optimaization of a wideband multisection quadrature directional coupler

In this paper, lumped elements equivalent circuit models are proposed for the distributed backward line and branch line directional couplers. Firstly, the conversion topologies have been developed from distributed microwave circuits to the lumped element circuits. Secondly, as applications of the proposed topologies, two 3dB lumped-element directional couplers have been generated. 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 the bandwidth.