Da Zhong

Characteristics of a novel kind of miniaturized cavity-cell assembly for rubidium frequency standards

A novel kind of cavity-cell assembly for rubidium frequency standards has been developed. The assembly utilizes a new magnetron-type microwave cavity. The cavity is of small size, easily manufactured with high machining precision, and the cavity frequency can be easily adjusted. Either the integrated filter technique (IFT) or the separated filter technique (SFT) can be used in this cavity-cell assembly. The assembly has a high signal-to-noise ratio. The frequency stabilities of rubidium atomic frequency standards with this assembly are 4times10 -12/tau1/2 for IFT and 2.7times10-12/tau1/2 for SFT, and its temperature coefficient and light shift are very low

Investigation on physics package with slotted-tube microwave cavity for rubidium atomic frequency standard

In this paper, a unique physics package using slotted-tube cavity for rubidium atomic frequency standard has been described, including its structure, characteristics and performances. Due to the advantages of high cavity Q factor, large microwave filling factor, stable light intensity and so on, the physics package has obtained a high signal-to-noise ratio. The test results suggest that RAFS using this physics package has achieved an excellent short-term frequency stability of 1.2E-12 / τ½ (1s≤τ≤100s).

A microwave cavity with low temperature coefficient for passive rubidium frequency standards

Cavity pulling effect has been fully considered in designing of various atomic frequency standards, but quite often it has been neglected for passive rubidium atomic frequency standards (RAFS). This situation may be acceptable for the commonly used RAFS but it is less so for high performance one. A new type of microwave cavity with low temperature coefficient (TC) was designed with coefficient of 28.2 kHz//spl deg/C, which is positive and nearly one order smaller than that of the traditional TE/sub 111/ cavity. Analyses show that the cavity pulling effect of the cavity can be neglected under reasonable temperature stabilization condition. The main cause of the small TC of the cavity was discussed, which is due to the compensation of the positive TC of the dielectric ring in the cavity to the negative TC of the metal part of the cavity.

Main features of space rubidium atomic frequency standard for BeiDou satellites

Wuhan Institute of Physics and Mathematics (WIPM) has been developing the space rubidium atomic frequency standard (RAFS) for BeiDou navigation satellite system since the late of 1990s. Design of the RAFS aims to realize high stability, small size, long lifetime, high reliability and space environmental adaptability. The physics package was designed in SFT scheme. A slotted tube cavity with small size and TE011 resonant mode was used to construct the cavity-cell assembly, and an argon lamp with long lifetime was used as the pumping source. The microwave chain includes a 10MHz VCXO, a 5.3125MHz synthesizer, a ×9 RF multiplier and a ×76 SRD multiplier. Electronic circuits were designed by using analog circuitry to minimize the risk of element failure in space. The day stability of the space RAFSs developed for BeiDou regional system distributes within 2~5×10-14. To meet the needs of BeiDou global system, design of the RAFS has been improved further. A slotted tube cavity with larger size and better resonant mode was used, the argon lamp was substituted with a filtered xenon lamp, and the phase noise of microwave chain was depressed further. A prototype of new generation space RAFS was built recently. Preliminary test showed that the day stability of the prototype has reached 3×10-15.

Demonstration of a Physics Package with High SNR for Rubidium Atomic Frequency Standards

The frequency stability of a rubidium atomic frequency standard (RAFS) depends mainly on the signal to noise ratio (SNR) of atomic discrimination signal provided by the physics package. In order to improve further the frequency stability of our RAFS, a new physics package with high SNR was designed recently. The physics package was designed based on an improved slotted tube cavity. Compared with our previous design, the new cavity has more uniform magnetic line distribution and larger size, so that a larger resonance cell can be used. In the design the separated filter technique (SFT) was used. A Helmholtz coil was substituted for a solenoid one to create a more uniform C field. At present a prototype of the physics package has been made. A preliminary test has been performed, and a short term frequency stability of 6 × 10−13/1 s was achieved. This result indicates that the SNR of the physics package could meet the requirement for building a RAFS with frequency stability better than 1 × 10−12/τ1/2.

Study of the Physics Package for High Performance Rubidium Frequency Standards

Frequency stability of an atomic frequency standard depends mainly on the Signal to Noise Ratio (SNR) of atomic discrimination signal. For a Rubidium Atomic Frequency Standard (RAFS), the SNR is closely related to the characteristics of the cavity-cell assembly in physics package. The RAFS in our laboratory is designed based on the slotted tube cavity, and a typical stability of 1.5 × 10−12 τ−1/2 (1–1000 s) has been achieved. The current cavity used in our design is of a disadvantage of field inhomogeneity. To improve further the stability of the RAFS, a modification of the cavity has been carried out. With this modification, the field homogeneity has been greatly improved, and the cavity size was increased also, enabling to hold a larger absorption cell. According to a theoretical evaluation, the SNR of physics package was enhanced by nearly two times, meeting the need to design a RAFS with a stability better than 1.0 × 10−12 τ−1/2.

A Subminiature Microwave Cavity for Rubidium Atomic Frequency Standards

A subminiature microwave cavity for rubidium atomic frequency standards has been developed. The cavity has volume of 8.1 cm3, and is of strong resonant signal with high Q factor. Based on the cavity a small size cavity-cell assembly with volume of 9.5 cm3 for rubidium frequency standards has been developed. A preliminary test showed that the cavity-cell assembly is of ability to achieve a short-term frequency stability of 3times10-11/radictau.