The sensing applications of nitrogen-vacancy color centers in a diamond require an efficient manipulation of the color center ground state over the whole volume of an ensemble. Thus, it is necessary to produce strong uniform magnetic fields of a well-defined circular polarization at microwave frequencies. In this paper, we develop a circularly polarized microwave antenna based on the excitation of hybrid electromagnetic modes in a high-permittivity dielectric resonator. The influence of the geometrical parameters of the antenna on the reflection coefficient and magnetic field magnitude is studied numerically and discussed. The Rabi frequencies and their inhomogeneity over the volume of a commercially available diamond sample are calculated. With respect to the numerical predictions, a Rabi frequency as high as 34 MHz with an inhomogeneity of 4% over a 1.2 mm × ∅2.5 mm (5.9 mm3 in volume) diamond sample can be achieved for 10 W of input power at room temperature. The antenna prototype is fabricated, and experimental investigations of its characteristics are performed in microwave and optical frequency domains. The circular polarization of the microwave magnetic field with an ellipticity of 0.94 is demonstrated experimentally. The Rabi oscillation frequency and its inhomogeneity are measured, and the results demonstrate a good agreement with the numerically predicted results.

Thin ferroelectric barium strontium titanate (BST) layers of high structure quality have been grown for the first time directly on semi-insulating silicon carbide substrates by RF magnetron sputtering of a ceramic target. The structural and microwave properties of the films were substantially improved by an intermediate annealing of the layers during the growing process. Prepared under this approach, BST films have a well-formed crystal structure, which has a positive effect on their electrical properties, specifically on nonlinearity and dielectric losses. Planar capacitors based on these BST films demonstrate the best combination of high tunability and low losses for BST/SiC structures at microwaves.

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Abstract-An electrodeless measurement technique of complex dielectric permittivity of high-K dielectric films is described. The technique is based on a quasi-optic Fabry-Perot resonator and modified for investigation of two-layer dielectric structures -substrate/K-film. This procedure is destined to be used for providing a simple intermediate control of parameters of high-K films before the following technological process. Regimes of measurements providing the most sensitive conditions for definition of film parameters are considered. The proposed method is tested on two-layer structures with wellknown parameters and is used for characterization of ferroelectric (Ba,Sr)TiO 3 films in the millimeter wavelength range (∼ 50 GHz).