A New Concept of Open ${\rm TE}_{011}$ Cavity

Abstract

The 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 TE 011 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 TE 011 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 TE 011 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.

High-frequency EPR applications of open nonradiative resonators

“…Therefore, the rescaling of this design to shorter wavelengths is not trivial. Even when these difficulties have been overcome by the adoption of ingenious technical solutions, the results do not satisfy theoretical expectations [9,16].…”

“…Consider now a hypothetical TE c 0 mode trapped in the central volume of the cavity. Such a mode cannot transfer energy to the cutoff-less transverse electromagnetic (TEM) modes propagating along the plates, since the TE c 0 mode does not have common field components with the TEM modes [16,26]. The radiative decay of the TE c 0 mode requires a coupling with the TE w 0 modes propagating along the parallel-plate waveguide (indicated by the superscript w), whose cutoff k cutoff is given by…”

“…As a general rule, it is possible to demonstrate that the NR resonators can support trapped modes with field distribution similar to that of the TE 011 mode of the closed cylindrical cavity. This is the case for structures with rotational invariance, which are indeed compatible with transverse electric (TE) modes [16].…”

“…Open resonators based on the concept of a nonradiative (NR) structure have been demonstrated to be a valid alternative to the standard single-mode cavities [16,24,25]. In the context of electromagnetic devices, a NR structure can be defined as an active region of similar size to the employed wavelength k, shielded by a metallic surface having large apertures.…”

“…In contrast to closed cavities, where the apertures which permit external excitation of samples are as small as possible in order to avoid significant redistribution of the modal fields, the aperture in a NR structure represents an essential element for the field distribution and confinement properties. The constraint limiting aperture size to be much smaller than k does not apply to NR structures, where it can be comparable to the resonant wavelength [16]. Despite the largely open character of the structure, the NR configurations can support trapped (i.e.…”