Systematic algorithm for the design of hybrid waveguide-microstrip transversal microwave filters

A novel algorithm to design hybrid waveguide-microstrip transversal microwave filters is proposed in this study. The idea consists in isolating each resonator involved in the filter structure, to synthesise individually its frequency response, both in resonant frequency and bandwidth. These separated optimisations lead to the dimensions of the filtering structure to meet the requirements of a certain, specified transfer function. The novel algorithm introduces an iterative procedure in order to synthesise the direct coupling term between source and load, which is always present in the hybrid filter structure. The whole algorithm is illustrated by means of a design example, where a very good agreement between the ideal specified transfer function and the final frequency response of the designed hybrid filter is obtained. A second different design example, which has been manufactured and tested, is also included for validation.