Design of Sum-Difference Power Combiners with Second-Order Filtering Functions

A design approach for sum and difference power combiners with filtering capabilities is introduced. It is based on a symmetric configuration that can be straightforwardly analyzed using ABCD matrices of the even and odd networks. The resulting four-port scattering matrix is compared to the respective transmission functions of a second-order filter which relates prototype coefficients to inverter values. The method is demonstrated at the example of a 23.9 GHz substrate integrated waveguide (SIW) combiner with sum and difference ports. Good agreement between results obtained from CST and a mode-matching technique validates the design approach.