Finite element analysis of an array of cylindrical rods or rectangular bars between ground planes

The structure of many microwave filters consists of arrays of cylindrical rods or rectangular bars located between parallel ground planes. In this paper, a design method and design data to synthesize filters such as interdigital and comb-line filters are presented. An analysis of these filters based on finite and infinite element methods is developed. Quasi-TEM mode, the lowfrequency propagation, along such a structure is described in terms of even and odd modes. A variational principle is used to compute the Normalized Maxwellian Capacitance Matrix Per Unit Length (NMCPUL). The NMCPUL may be used to synthesize filters. The results obtained by the present method agree with the reported results in the literature.