New Design of Waveguide Directional Coupler Using Genetic Algorithm

In this letter a novel design method for waveguide directional coupler is proposed based on genetic algorithm. Using the proposed method, a waveguide directional coupler with desired coupling coefficient (
$C$
), has been designed, so that maximum mean value of directivity (
$D$
) is achieved in the frequency range. In this method, a specified patterned aperture, which can be determined using genetic algorithm, couples power between two parallel waveguides. In order to extract specified pattern of coupling aperture, coupled magnetic field integral equation in term of surface magnetic current is derived and solved by method of moments to obtain general scattering matrix and then coupling coefficient and directivity of directional coupler are calculated. The proposed patterned aperture compared with conventional circular hole directional coupler of the same length, has been improved the mean value of directivity around to 137.7% for a given coupling coefficient. The performance of the proposed method is verified with the results of simulation. To validate the simulation results, a waveguide directional coupler using patterned aperture is designed, fabricated and measured.