Full-wave CAD of in-line symmetric and asymmetric triple-mode circular waveguide filters

A new triple mode in-line principle for filter application that provides a versatile configuration is developed. The position in the z-axis of the cross section that includes the coupling screws is considered as a parameter of design. In addition, the length of the cavity is used as a tuning element. Symmetrical and asymmetrical responses can be accomplished. The combined MM–FEM (mode-matching finite-element method) has been employed for the design. Special attention is devoted to the circuital model in order to save a great deal of computational effort. Two experimental filters have been designed and constructed. The results show excellent agreement with theory, and corroborate the validity of the proposed topology. ©1999 John Wiley & Sons, Inc. Microwave Opt Technol Lett 20: 135–140, 1999.