Efficient and Accurate Calculation of the Cutoff Wavenumbers of Coaxial Elliptical-Circular and Circular-Elliptical Metallic Waveguides

In this paper, we propose an efficient method for the calculation of the cutoff wavenumbers of coaxial elliptical-circular and circular-elliptical metallic waveguides. The cutoff wavenumbers are obtained through closed-form expressions making the evaluation efficient, and moreover, very accurate even for large values of the eccentricity of the elliptical boundary. The resulting formulas are free of Mathieu functions, including only simple algebraic expressions with Bessel functions, and are valid for every different value of the indices n and m, corresponding to every higher order TMnm or TEnm mode. The validation of the method is performed by comparing to the general exact solution. The efficiency and accuracy of our method is presented by illustrative examples. Numerical results are given for the cutoff wavenumbers of various higher order modes.