EXCITATION OF AN ARBITRARY-CROSS SECTION DIELECTRIC WAVEGUIDE AT NEAR-CRITICAL FREQUENCIES.

Characteristic modes of dielectric waveguides are divided into three classes which are defined by their behavior near critical frequencies. At these frequencies the dispersion equation for modes of a given class is identical for all waveguides. As the frequency aproaches its critical value, the frequency behavior of the amplitude of a characteristic mode, excited by any local sources, is determined only by the class to which that mode belongs. The function which describes the decay away from the source of the so called additional field, which exists in a waveguide together with the characteristic modes, has also a universal character at near critical frequency of any generated mode.