Microwave building block filters using genetic optimization

The filters are composed of a cascade of non-loaded rectangular cavities where several resonant modes are considered. The cavities are interconnected through rectangular waveguide sections. All resonant modes are used near their cutoff frequencies to reduce the size of the filters. Rather than relying on modeling the coupling coefficients between cavities, the technique is based on defining multimodal scattering matrices for all the building blocks composing the filter. The main building blocks are simple rectangular waveguide sections and change in cross section dimension discontinuities. A fast custom simulator based on the scattering matrices was developed and was used with an optimization method based on the genetic algorithm to design filters with Generalized Chebsyhev type characteristics. A 14 GHZ forth order filter with two transmission zeros as well as a 20 GHZ seventh order filter with four transmission zeros were designed and built and their measured responses are provided.