Computer Optimization of Inhomogeneous Waveguide Transformers

The problem of designingbroadband mtdtisection stepped rectrmgrdar waveguide impedance transformers, when the input and output gnides have different cutoff frequencies but propagate the same mode, is formulated in general terms for direct optimization hy digital computer. The formulation is sufficiently flexible to allow nonideal junction discontinuity effects and mismatched terminations to be taken into account doring optimization, Constraints placed on the width, height, or length of any section need he dictated ordy by considerations for dominant mode propagation and the requirement of small (hut not necessarily negligible) jonction disconthmities. The objective of the present formrdation is a minimax equal-ripple response over a predetermined frequency band satisfying the constraints seleeted for the particular problem. The ripple search strategy to locate the maximum reflection coefficient within the band and the razor search strategy to minimize it, as described by Baodler and Macdonald [8] in another paper, were employed. Constrained optimum equal-ripple sohrtions to examples previously published by Yoong [2]-[4] Matthaei et al. [4] and Riblet [5] are presented. They demonstrate the considerable improvements made possible hy the present formulation with regard to performance, reduction in number of sections, and physical size. The approach used in this paper should also find application in the design of broadband microwave matching or equalizing networks consisting of noncommensurate components and for which exact synthesis techniques may be unavailable.