FULL-WAVE COMPUTER-AIDED-DESIGN OF WAVE-GUIDE COMPONENTS BY CIRCUIT SIMULATION

This article reviews a full-wave equivalent circuit formulation for a large class of rectangular waveguide components and its implementation in a commercial circuit simulator. The full-wave equivalent circuit f ormulation represents a direct implementation of the mode-matching tec hnique in terms of ideal dependent voltage and current sources and mod al transmission lines. It enables rigorous and efficient full-wave ana lysis of waveguide components such as iris-coupled filters, metal inse rt fillers, couplers, and phase shifters, directly and entirely by cir cuit simulation. In addition, available design and optimization featur es of the CAD tool can be fully exploited. The paper reviews the deriv ation of the equivalent circuit models for single and cascaded step di scontinuities and describes the generalization to single and cascaded bi-and n-furcations including metal inserts. The method has been imple mented in the microwave circuit simulator Libra and applied to several waveguide structures, including a four-iris bandpass filter for the K a-band. Excellent agreement between the circuit simulation solutions a nd the results from a stand-alone mode-matching code is found. To demo nstrate the design capabilities with the circuit simulation approach, the bandpass filter has been redesigned and optimized by using the ava ilable design and optimization features of the commercial CAD tool. (C ) 1998 John Wiley & Sons, Inc.