RADIO PHYSICS AND RADIO ASTRONOMY

Subject and Purpose. The subject of the work is the behavior of "bouncing ball" oscillations and surface oscillations in open resonant systems with curvilinear reflectors embedded in the waveguide transmission line. We seek to determine physical patterns and features of the interaction between volume "bouncing ball" oscillations and surface oscillations in open resonant systems with curvilinear reflectors.

Methods and Methodology. Basic quasi-optical techniques were employed. The electric field structures of considered oscillation types were measured using the probe-induced perturbation method. The resonant transmission coefficients of the open oscillating systems and the physical phenomena within them were experimentally studied with the aid of well-known microwave measurement techniques.

Results. A hemispherical open resonator (OR) and a mirror-lens resonator (MLR) have been studied to find that surface oscillations in both resonators are excited on the curvilinear surfaces of the reflectors and interact with the "bouncing ball" oscillations under certain conditions. In the hemispherical OR, this interaction occurs when α/2w₁ =  0.927, where α is the radius of the curvilinear reflector aperture and w₁ is the radius of the fundamental mode field spot on this reflector. In the MLR, the interaction between the fundamental mode oscillation and the surface oscillation localized on the lens surface is observed when α/2w₁ = 1.351. 

Conclusions. The condition of small diffraction loss in the OR is known to be α/2w₁ ≥ 1, and the possibility of the excitation of surface oscillations in the OR must always be considered because surface oscillations may mislead the researcher when examining solid dielectric specimens for the electrophysical parameters using the OR method. Thus, it is advisable to hold L/R ≤ 0.73 in the hemispherical OR case and L/F ≤ 0.65 in the MLR case.

Keywords: open resonator, mirror-lens resonator, surface oscillations, "bouncing ball" oscillations, resonant transmission coefficient, interaction of oscillations

Manuscript submitted 14.11.2024

Radio phys. radio astron. 2025, 30(1): 065-073

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