Analysis of a Double Folded Stub Microstrip Structure using Generalized Transmission Line Equations Method

Abstract

This paper presents a generalized transmission-line theory which is useful to describe the local radiation effect along almost arbitrary three-dimensional wire structures. For the generalized transmission-line theory, the mathematical structure of the classical telegrapher equation is preserved, while the coefficients (the per-unit-length parameters) are generalized in order to represent the intrinsic behavior of the wire structure. Essentially, the generalized transmission line equations (GTLEs) is a novel kind of telegrapher equation. The equation coefficients of the generalized transmission line equations (GTLEs) are determined from full-wave numerical solutions in this paper. In comparison with the conventional telegrapher equation, the GTLEs has two additional terms — dependent series voltage and shunt current sources — which represent local radiation effect from discontinuities of the nonuniform transmission-line itself. For the double folded stub microstrip structure, the novel 1D-GTLEs whose coefficients are determined by dynamic numerical methods can have broadband frequency characteristics. To the investigated microstrip structure as a band stop filter, the S parameters for a frequency band from 3 GHz to 18 GHz can be calculated by using only one group of the 1D-GTLEs at a frequency of 12 GHz, while 1D-GTLEs is only established on the central transmission line rather than on the whole structure with the stubs. Furthermore, the 2D-GTLEs developed from the 1D-GTLEs is sought for the whole structure with stubs and the model of 2D-GTLEs is validated to be more accurate than that of 1D-GTLEs through numerical experiments in this paper