Finite-element modeling for the design optimization of microwave filters

This paper outlines an electromagnetic optimization technique dedicated to the design of microwave bandpass filters. The purpose is to determine the optimal dimensions of the electromagnetic model. Applying this technique, the geometrical dimensions of the distributed structure are accurately determined, and no experimental readjustment is necessary. The optimization procedure combines an electromagnetic analysis and a parameter extraction. The analysis method is a finite-element modeling coupled with a frequency parameterization technique for improving the computation time. The parameter extraction method is based on the approximation of the simulated scattering matrix and on the synthesis of the equivalent electrical network. The comparison between extracted and ideal networks enables to converge the optimal dimensions. The procedure is applied to design a dual-mode waveguide filter. In this case, within the electromagnetic model, the screws are taken into account using lumped elements which may be adjusted independently.