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A convenient form of spatial‐domain Green’s function for a point charge in multilayered dielectric medium enclosed by a conducting cylinder of circular cross‐section is presented in this paper. Green’s function expression is obtained by solving Poisson differential equation in cylindrical coordinates and applying analogies with multistep electrical transmission lines. Convergence of the proposed expression obtained in the form of a double infinite sum is investigated and compared with triple‐sum solution for the same problem obtained by standard variable separation method. The numerical investigation has shown that the proposed expression has much faster convergence than the standard solution. Also, contrary to the variable separation method, increasing the number of dielectric layers is not an obstacle in determining of proposed Green’s functions, as it is shown for the three layers dielectric structure.

An improved model for microwave interdigital filters design and analysis is developed by correction of Denig’s procedure (1989). This model enables correct modeling multiple‐coupled transmission line structures as parallel sections of single coupled lines. Also, it is very suitable for the design and analysis of the filters by means of widely used microwave CAD programs. In this way the design and analysis of the microwave interdigital filters are significantly simplified. The verification of modified Denig’s procedure is carried out through the two examples of the microstrip interdigital bandpass filters by means of program package LIBRA.