Observation of Excitation of Eigenmodes in Surface-Wave Resonators Having the Cylindrical Geometry

We present the results of theoretical and experimental studies of the surface-wave Ka-band resonators which are formed by sections of cylindrical waveguides with single-period wall corrugations. The electrodynamic characteristics of such resonance cavities are analyzed within the quasioptical approach and three-dimensional simulation by the finite-difference time-domain method. The results of the theoretical analysis agree quite well with the experimentally measured frequency dependences of the reflection coefficients, which demonstrate the existence of surface modes with different numbers of longitudinal field variations. The measured Q-factors and frequencies of the above-specified modes corresponded well to the calculated values. In order to perform “cold” electrodynamic tests, wideband waveguide converters of the TE mode of the standard rectangular waveguide to the TM mode of an oversized cylindrical waveguide, which have a sufficiently low level of ohmic loss at a conversion efficiency exceeding 95% in the 34–40 GHz frequency range, were manufactured by the the 3D printing method.