2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/110496The confinement properties of the open structure formed crossing a circular waveguide perpendicular to a parallel-plate waveguide are discussed, highlighting the fundamental differences with respect to the common high-frequency resonators. Among the electromagnetic modes trapped at the intersection region of the two waveguides, the TE011 one appears as the most appropriate for high-frequency applications. The experimental characterization of this mode is described in detail, investigating the response of a millimeter wave configuration resonating at 281 GHz, which shows state-of-the-art performances. The properties of the TE011 mode are studied in terms of the geometry, calculating the mode chart and the related quality factor and power-to-field conversion efficiency. The mode chart is then determined for configurations including a sample holder, in which one of the component waveguides is filled with a low-loss dielectric material. The TE011 mode reveals in general remarkable merit figures, as well as a significant stability with respect to the geometrical imperfections and to the insertion of a sample holder. The obtained results show that the proposed single-mode resonator competes with the standard cavities in terms of performance, versatility, and simplicity.17 pages, 7 figures. New version with higher frequency measurementsInstrumentation and Detectorstext