Analysis of higher-order modes in coaxial conical transmission line

Analysis of cutoff characteristic for TE wave and TM wave is very important to design the geometry of structure (the angle of the cones) for TEM cell. In the paper, take the co-conical line for example. The half angle of inner conical conductor is 10° and that of outer conical conductor is 1.893°. An iteration method programmed in Matlab is used to solve the roots of the transcendental functions. Then the wavelength of the first three TE modes and TM modes is obtained. The cutoff phenomena in conical lines occur gradually, which is related to frequency and spatial location. The first mode is TE
₁₁
mode with cutoff wavelength 0.65r that is the same with solution presented by NIST. Therefore the calculated method can be proved effectively.