An Improved Helical Resonator Design for Rubidium Atomic Frequency Standards

The slow-wave structure (SWS) can be used as the resonant cavity for rubidium atomic frequency standards (RAFSs), in which the longitudinal component of the magnetic field can enable the rubidium atoms' participation in the stimulated transitions. In this paper, an improved helix SWS based on good propagation characteristics as a helical resonator for RAFS is designed. The theoretical analysis is performed together with the simulations of the propagation characteristics. Using finite integration technique (FIT), the simulated results, including phase velocity, on-axis interaction impedance, and distribution of the magnetic field, are implemented and compared with the experimented results. The effects of the different helical pitch and dielectric material in the insulator cylinder on the propagation characteristics are analyzed in detail. The analyzed results show that smaller helical pitch and proper usage of dielectric material in the insulator cylinder can make the propagation characteristics of the helix SWS superior. The improved helix SWS for RAFS adapts a smaller helical pitch and is loaded with the dielectric material of Teflon in the insulator cylinder. This structure can reduce the cavity volume to 14.7 cm(3). The short-term stability of RAFS is up to 1.28 x 10(-12)/tau(1/2), and the frequency stability is 2.0 x 10(-10)/degrees C at the temperature range of -20 degrees C to +55 degrees C.