Evaluation of cut-off frequencies of higher order modes in eccentric coaxial line

The paper presents a method of evaluation of the cut-off frequencies of higher order modes of transmission lines having eccentric annular cross-section using a combination of conformal transformation and the method of finite difference. The Laplacian operator appearing in the weighted Helmholtz equation resulting from the conformal transformation is represented as a five-point difference operator of unequal arm length along the two axes. The eigenvalues which give cut-off frequencies are evaluated from the characteristic equation expressed in terms of matrices obtained from a set of simultaneous equations satisfying the boundary conditions. Comparison of numerical data is presented.