EVALUATION OF CUTOFF FREQUENCIES OF HIGHER-ORDER MODES IN ECCENTRIC COAXIAL LINE

The paper presents a method of evaluation of the cut-off frequencies o f higher order modes of transmission lines having eccentric annular cr oss-section using a combination of conformal transformation and the me thod of finite difference. The Laplacian operator appearing in the wei ghted Helmholtz equation resulting from the conformal transformation i s represented as a five-point difference operator of unequal arm lengt h along the two axes. The eigenvalues which give cut-off frequencies a re evaluated from the characteristic equation expressed in terms of ma trices obtained from a set of simultaneous equations satisfying the bo undary conditions. Comparison of numerical data is presented.