The multimode equivalent network (MEN) formulation has been originally developed for the efficient and accurate analysis of waveguide devices. In this article, we extend the use of the MEN to the analysis of zero-thickness, planar printed circuits in a metallic enclosure. The formulation is developed for metallic areas of arbitrary shape and includes both internal and external ports in the transverse plane to model connections to external components, and coaxial input/output ports. The boundary integral resonant mode expansion (BI-RME) method is used for the analysis of the arbitrary shape metallizations. On this basis, shielded multilayered microstrip circuits of complex geometry are analyzed in the common frame of the MEN technique. To validate the theoretical formulation, several boxed microstrip structures are analyzed, including multilayered configurations with several metallization interfaces, showing good agreement with respect to both other commercial tools, and measurements. Index Terms-Integral equations (IEs), method of moments (MoM), microwave filters, monolithic microwave integrated circuits (MMICs), multimode equivalent networks (MENs), numerical methods, planar junctions.
I. INTRODUCTIONC URRENTLY, computational electromagnetics (CEM) techniques [1], [2] are widely used to save development time and manufacturing costs in the microwave industry. In this context, therefore, new more efficient numerical methods for the design of microwave components are of Manuscript