Irregular-waveguide elements coupling high-Q resonators with single-mode waveguides

A new type of element coupling a high-Q resonator with single-mode rectangular waveguides is proposed. The element is an irregular tapered section. A technique of electrodynamic calculation of such a coupling element is described. The element is experimentally investigated in the case of two-mirror open resonators. The high efficiency exhibited by the coupling element over a wide frequency band is confirmed by theoretical calculations and demonstrated experimentally.