Field theory CAD of L-shaped iris coupled mode launchers and dual-mode filters

A rigorous field theory design method for L-shaped iris-coupled TE/sub 10/-to-TE/sub 01/-mode launchers and dual-mode filters is presented. The theory is based on the full-wave mode-matching key-building block S-parameter description of the L-shaped iris in rectangular waveguides and allows, in association with the generalized S-matrix technique, the complete three-dimensional modeling of L-shaped structures and cascaded discontinuities. Arbitrary obstacle location and finite thickness are rigorously taken into account. An optimized design example of a very compact Ku-band (12-18-GHz) mode launcher achieves 5% bandwidth with more than 20-dB return loss at the 90 degrees -twisted WR62 input and output waveguides. The computer-optimized design of a Ku-band L-shaped iris coupled four-pole dual mode filter demonstrates good elliptic function behavior. The theory is verified by measurements.<>