RADIO PHYSICS AND RADIO ASTRONOMY

Subject and Purpose. The behavior of axially symmetric oscillations in a hemispherical open resonator (OR) integrated into a waveguide transmission line and operating in pass-through mode is studied. The apertures of the OR mirrors are 60 mm. The radius of curvature of the spherical mirror is 85 mm. Two 3.6×0.17 mm slot coupling elements are positioned symmetrically about the OR axis and 13.2 mm away from it. The axially symmetric oscillations excited in a hemispherical OR by slotted coupling elements are analyzed with the view of characterizing dielectric materials using resonant methods in the EHF range.

Methods and Methodology. Basic quasi-optical techniques are adopted. Namely, the electric-field structures of oscillation types are measured by the perturbation method. The resonant transmission coefficients of open oscillatory systems and the physical phenomena occurring within them are experimentally studied using standard microwave measurement techniques.

Results. In the experimental study conducted at 70.622 GHz, OR oscillations with large transverse indices were identifi ed from amplitude distributions. The perturbation method was used with a 1 mm diameter probe. It has been shown that in non-axial OR excitation, axially symmetric oscillations, among others, are excited. Experimentally, a distinctive feature of those axially symmetric oscillations has been established, which is an area with zero electric-field intensity at the center of the cavity. For the investigated TEM*_0,1,12 oscillation, this area is 6 mm in diameter.

Conclusions. It has been demonstrated that an open resonator with axially symmetric oscillations is effective for measuring the electrophysical parameters of materials, including liquids. It has been established that the placement of a disk-shaped sample or a liquid-filled cuvette at the center of the flat mirror of a hemispherical OR not only does not disrupt the working oscillation but additionally contributes to the angular mode selection of the OR oscillation spectrum. The hemispherical OR, as considered, can also be used for dynamic quality control of various liquids. In this case, the holder, like a quartz glass tube, is positioned along the OR axis.

Keywords: millimeter-wave range, open resonator, modes, coupling element, transmission coefficient, probe

Manuscript submitted  14.09.2025

Radio phys. radio astron. 2025, 30(4): 285-295

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