Global modeling of a periodic coplanar waveguide structure for filter applications using an efficient iterative procedure

Abstract

INTRODUCTIONA coplanar waveguide (CPW) has an important utility for monolithic microwave integrated circuits (MMIC) conception, due to its several attractive features in contrast to microstrip lines, such as ease of fabrication and simplicity of integration with active devices. Thanks to the uniplanar features, CPW offers several advantages in comparison with microstrip lines, such as easy series, shunt connection, and low dispersive effects.Several designs for coplanar waveguide including symmetric, asymmetric CPW, and multilayered CPW [1,2]. The recent development of uniplanar technology has offered more simplicity for circuit designers. The need for circuits of small size and high efficiency has generated much attention to the study of compact coplanar filter. Recently, some basic compact structures utilized as series resonators in uniplanar technology have been proposed by K. Hattek et al. [3]. proposed the design of a novel ribbon-of-brick-wall coplanar waveguide filter. The filter is built from cascading several sections of quarter-wavelength openend series stubs. In 1991, Dib et al. [5] applied the space-domain full-wall-wave integral equation to calculate the scattering parameters of the stubs. From the computation results, they used curvefitting technique to guest the equivalent circuits model. Rayit et al.[6] used the simulator EM to calculate the scattering parameters but suggested another equivalent circuit models.In this paper, a global modeling of a filter for uniplanar technology is considered by using a new iterative method based on the wave concept denoted as WCIP [7][8][9]. These filters are realized by considering one and three periodic cells. The periodic structure on CPW offers a very low insertion loss; thus, it can be used for several applications in microwave functions and help to reduce the MMIC size. THEORYDuring the last few years, the FMT-WCIP method has been applied in a wide variety of microwave structures [8,9]. In the following, we summarize the mechanism of the iterative procedure.Let us consider a CPW structure where the circuit is considered on the air/dielectric interface, as shown in Figure 1. The regions on both sides of ⍀ are designed by regions 1 and 2. Each region is defined with its characteristic admittance y 0i , which is chosen equal to 1/120 ri . The circuit includes three subdomains: metal M, insolate I, and source S. The solution of the problem consists in satisfying the following boundary conditions:On the planes z ϭ ϩH 1 and z ϭ ϪH 2 , the higher-order modes are shunted by their reactive admittance Y, which relates the tangential electric field E T to the total current density J; hence, we obtain:where i corresponds to regions 1 or 2, and Y is a projector operator on the f mn TE and f mn TM modes of the empty waveguide. The wave concept is introduced by considering the following linear combination [8]:This last equation allows us to write the boundary conditions given by Eq. (1) as the following general spatial equation:By combining Eqs. (2) and (3), a spectral ...

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