The Intrinsic Impedance and Its Application to Backward and Forward Coupled-Line Couplers

The even-odd-analysis of a reciprocal and twofold symmetrical four-port provides four eigenimpedances. A method for the derivation of the intrinsic impedance of the network from these eigenimpedances is shown. Once the conjugate complex of its intrinsic impedance is presented to the external ports of the network, it will be a quadrature coupler. The usefulness of the intrinsic impedance is shown exemplarily by two detailed examples: the improvement of the directivity of microstrip coupled-line couplers and the development of forward coupled-line couplers. Approaches for the broadening of the bandwidth are shown. All couplers presented achieve superior performance regarding directivity, return loss, and bandwidth.