Wideband Representation of Passive Components Based on Planar Waveguide Junctions

Abstract

Modern microwave and millimeter-wave equipment, present in mobile, wireless and space communication systems, employ a wide variety of waveguide components (Uher et al., 1993; Boria & Gimeno, 2007). Most of these components are based on the cascade connection of waveguides with different cross-section (Conciauro et al., 2000). Therefore, the full-wave modal analysis of such structures has received a considerable attention from the microwave community (Sorrentino, 1989; Itoh, 1989). The numerical efficiency of these methods has been substantially improved in (Mansour & MacPhie, 1986; Alessandri et al., 1988; Alessandri et al., 1992) by means of the segmentation technique, which consists of decomposing the analysis of a complete waveguide structure into the characterization of its elementary key-building blocks, i.e. planar junctions and uniform waveguides. The modeling of planar junctions between waveguides of different cross-section has been widely studied in the past through modal analysis methods, where higher-order mode interactions were already considered (Wexler, 1967). For instance, in order to represent such junctions, the well-known mode-matching technique has been typically formulated in terms of the generalized scattering matrix (Safavi-Naini & MacPhie, 1981; Safavi-Naini & MacPhie, 1982; Eleftheriades et al., 1994). Alternatively, the planar waveguide junction can be characterized using a generalized admittance matrix or a generalized impedance matrix, obtained either by applying the general network theory (Alvarez-Melcon et al., 1996) or by solving integral equations (Gerini et al., 1998). A common drawback to all the previous techniques is that any related generalized matrix must be recomputed at each frequency point. In the last two decades, several works have been focused on avoiding the repeated computations of the cited generalized matrices within the frequency loop. For instance, frequency independent integral equations have been set up when dealing, respectively, with inductive (or H-plane) and capacitive (or E-plane) discontinuities (Guglielmi & Newport, 20