Analysis and Design of SIW Components Based on H-Plane Planar Circuit Approach 211 Analysis and Design of SIW Components Based on H-Plane Planar Circuit Approach

A waveguide whose sidewalls are replaced with densely arranged metallic posts has been proposed. This guide enables the easy realization of circuit patterns by the arrangement of metallic posts periodically in a parallel-plate waveguide or a grounded dielectric substrate. This type of waveguide is called the post-wall waveguide (PWW) (Hirokawa & Ando, 1998;Ando et al., 1998) or the substrate integrated waveguide (SIW) (Wu, 2001; Deslandes & Wu , 2005). This SIW technology is applied to a feed waveguide for a slot array antenna, or a leakage wave antenna. In particular, recently, for the purpose of making use of merits such as low loss, low cost, and high-density integration of microwave and millimeter-wave components and subsystems, a SIW short-slot 90° hybrid coupler, and a six-port receiver consisting of the 90° couplers and/or power dividers have been developed. Since this technology is a relatively new concept, it is desired that more SIW circuit components and subsystems appear to open a new vista (Xu et al., 2005; Moldovan et al., 2006). With regard to the analytical method of the SIW structure, the derivation of the propagation constant for the straight section of the guide has been studied on the basis of the Galerkin's method of moment (Hirokawa & Ando, 1998). Then widths of the SIW structure that is equal to the cutoff frequency of the rectangular waveguide with perfectly metalized sidewalls have been obtained. Also, empirical equations for the equivalent widths have been proposed through experiments and simulations (Xu & Wu, 2005; Cassivi et al., 2002). In (Xu & Wu, 2005), the FDTD method and the multimode calibration method are used to analyze the dispersion characteristics of the complex propagation constants of the SIW structure. However, in the case of designing and analyzing the circuit components for practical use, a full-wave em-simulator (Ansoft HFSS) has been employed (Moldovan et al., 2006). Since the simulation requires a relatively long computing time, it is desirable to develop a faster solver for the optimization requiring recursive computations. In this study, an analysis of the SIW structure is attempted by applying the analytical technique of the H-plane waveguide discontinuities based on the planar circuit approach (Kishihara et al., 2006; Kishihara et al., 2004). This technique can reduce the computation 10