Network analysis and design theory of aperture-coupled cavity-fed back-to-back microstrip directional coupler

A network analysis and design theory of an aperture-coupled cavity-fed back-to-back microstrip directional coupler was presented for the efficient and optimized design. For this purpose, an equivalent network was developed, and simple but accurate calculation of circuit element values was described. Based on this equivalent circuit, design equations of the coupler were derived and applied to design a 10 dB directional coupler. The hybrid optimization method based on the genetic algorithm and the Nelder-Mead method was invoked to treat several design parameters simultaneously. Good agreements between the measured and the specifications fully validated the proposed network analysis and design procedure.