Designs of a miniaturized sapphire-loaded cavity for space borne hydrogen masers

The previous compact hydrogen maser with sapphire microwave cavity in the Beijing Institute of Radio Metrology and Measurement is not suitable for a space application in navigation systems since a bit large volume and weight. In order to reduce the total size of hydrogen maser atomic clocks further, in this work, the authors have performed the detailed analysis and some theoretical and experimental result in optimizing parameters in a TE011 mode sapphire-loaded cavity resonator more suitable for space borne hydrogen maser. The minimization of the total cavity volume and maximization of the quality factor are both sought finally. Methods of theoretical calculations, finite element simulation, and related experiments have been performed in the process of designing a sapphire loaded cavity. Based on the analysis, a miniaturized sapphire microwave cavity with the total volume of 3.04 dm3, the quality factor 67500, and frequency-temperature coefficient -59.7 kHz/square is developed. The experimental results are completely consistent with modeled values. In addition, the theoretical calculation result shows that the product of the z-component of the magnetic energy filling factor in the bulb region and the cavity TE₀₁₁ mode Q-factor is 4.08E4 at 50 square in the designed miniaturized sapphire cavity. In addition, two sapphire loaded cavities in the NICT, Japan and in IRCOM, France are detailedly compared with that of our designs.