New Type of Evanescent Modes in Fin-Lines

It is shown that complex modes, which are known to exist in rectangular and circular waveguides with dielectric inserts, can also exist in fin -lines. These modes exist always in pairs with complex conjugate propagation constants of opposite signs. The electric field of one mode of such a pair does not couple to its own magnetic field, but to the magnetic field of the other mode in such a way that the total power transmitted by the two modes is purely reactive.