Designs of a miniaturized sapphire-loaded cavity for spaceborne hydrogen masers

The previous compact hydrogen maser with sapphire microwave cavity at the Beijing Institute of Radio Metrology and Measurement was not suitable for a space application in navigation systems with limitations on volume and weight. To resolve this problem, we present a new design of the sapphire-loaded cavity with optimal parameters in the minimization of volume and maximization of the quality factor. Methods of theoretical calculations, finite element simulation, and related experiments were performed in designing the sapphire-loaded cavity. Based on the analysis, a miniaturized sapphire microwave cavity with the total volume of 3.04 dm³, the quality factor 67 500, and frequency-temperature coefficient -59.7 kHz/??C is developed. The experimental results are completely consistent with calculation 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 40 800 at 50??C in the miniaturized sapphire cavity. In addition, 2 sapphire-loaded cavities in the Japanese National Institute of Information and Communications Technology and in the Microwave and Optical Communication Research Institute at the University of Limoges, France, are compared with that of our designs.