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The quality factor of concentric resonators

DOI 10.18127/j00338486-201907(10)-06


V.V. Komarov – Dr. Sc.(Eng.), Departament «Radio Electronics and Telecommunications», Yuri Gagarin State Technical University (Saratov); Leading Researcher, NIKA-Microwave, Ltd (Saratov)
S.K. Bushanskiy – Post-graduate Student, Yuri Gagarin State Technical University (Saratov)

In contrast to classical rectangular, cylindrical and re-entrant cavity resonators, weak studied concentric cavity resonators (CCR), the most well known among which is the spherical concentric cavity, have not found yet wide practical application in microwave engineering. Such metallic resonators are designed on a basis of simple shaped cavities with additional spherical inclusion in the central part of structure. Different numerical techniques like, for example, finite element method, finite difference time domain method, finite integration method, etc are usually employed to study electromagnetic properties of resonators with complicated configuration. Electrodynamic characteristics, namely resonant frequency and unloaded quality factor as a function of sizes of three microwave concentric cavities: rectangular, cylindrical and spherical made from copper, aluminum, nickel and brass in Ka-band (26,5…40 GHz) have been simulated numerically in the present study. Particular cases: cubic cavity and cylinder with equal height and diameter were analyzed for two of them. Simulations were carried out by means of 3D finite element models and commercial software COMSOL V.5.2. Numerical data are represented for two lowest TE- and TM-modes. Preliminary testing of 3D numerical models has been performed on examples of three classical microwave metallic resonators: rectangular, cylindrical and spherical, for which analytical solutions are available in the literature, and a re-entrant resonator. Comparison has demonstrated a good agreement of numerical and analytical solutions. Numerical results: dependencies of a resonant wavelength and a Q-factor as a function of normalized dimensions of all three resonators under study, have shown their advantages in comparison with classical metallic resonators of simple shape. In particular, CCR exhibit higher values of resonant wavelengths what allows designing microwave devices with smaller dimensions at fixed frequency. Moreover they have higher Q-factor values than rectangular and cylindrical cavities of the same size, as CCR.

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