New type of eigenoscillations and total-transmission resonance through an iris with below-cutoff hole in a rectangular waveguide

The total-transmission phenomenon of the main mode of a rectangular waveguide through a below-cutoff hole in the waveguide shorting before the point of occurrence of the higher-order waveguide modes is found. The effect is due to generation of high-Q eigenoscillations at the evanescent E₁₁ mode and is originated from a specific oscillation formed near a step junction of two waveguides, namely a larger single-mode waveguide and a smaller below-cutoff one. The iris composed of such two junctions is longitudinally symmetric. Thus, a pair of resonances occurs in accordance with the existence of a pair of symmetric and antisymmetric field distributions at the iris. Analogy with the recently found effects in double-periodic gratings with small holes is revealed. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 51, No. 2, pp. 111–121, February 2008.