Modes analyses of cylindrical waveguides using the MFCM

An efficient modes analyses technique for isotropic or anisotropic material filled 2D metallic waveguides with an arbitrary contour using the multifilament current method (MFCM) is presented. The ideal PEC boundary of a 2D waveguide is replaced by a shell with a high conductivity and electrical small thickness. The thin lossy shell not only can well approximate the boundary condition of PEC waveguide wall therefore without altering the initial waveguide modes, but also can let the external excitation penetrate through to excite the inside modes, resulting in a high internal field intensity at the frequency of each mode. In this case, the modes are revealed by the peaks of field intensity responses, and the spurious modes which existed in traditional source-free modes determination techniques can be completely avoided. Based on this idea, a generalized impedance boundary condition (GIBC) is formulated to represent the lossy waveguide wall and further utilized in the MFCM for simulating the internal field intensity over frequency. Three different configurations of a 2D waveguide are considered. The computed modes are compared with that obtained from commercial software, and an excellent agreement is achieved, yet an competitive advantage on simulation performances is observed by using the proposed technique.