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 1990's. 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 RAFS's 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.
Rubidium Frequency Standard for the GPS IIF program and modifications for the RAFSMOD Program
PerkinElmer provides the rubidium frequency standards (RFS) for the Boeing Block IIF GPS navigation satellites. The PerkinElmer RFS-IIF is the latest generation of its high performance rubidium clocks which have performed very successfully on board the block IIR GPS space vehicles for more than 10 years.The RFS-IIF output is the traditional 10.23 MHz rather than the =13.4 MHz "natural frequency" utilized for block IIR. This necessitated the addition of a secondary phase lock loop (PLL) synthesizer to convert the Rb natural frequency to 10.23 MHz. One main design challenge was to add this new section with a minimum impact on size, weight, power, performance, radiation hardness, reliability and design heritage. The second major change in the RFS-IIF was to make a significant improvement in the medium to long term stability by using Xenon lamp buffer gas and a thin-film spectral filter in the physics package to reduce shot noise and improve the signal-to-noise ratio (S/N). This has lowered the white FM noise level to below 1x10-12tau1/2. This paper describes the RFS-IIF design, the changes and improvements made, and the test results obtained. It also discusses the recent redesign activities to eliminate obsolete parts in the RFS-IIF as well as improvements and updates to the PerkinElmer test facility funded by the USAF GPS Wing (GPSW) under the Rubidium Atomic Frequency Standard Modification (RAFSMOD) Program.
Simulation study of high power microwave generation by virtual cathode oscillation in coaxial vircator
Summary form only given, as follows. We have numerically simulated the high power microwave generation by virtual cathode oscillation in a coaxial vircator with 3 dimensional PIC code Magic. It is noted that the coaxial vircator has the advantage of an enhancement of power efficiency and gaining of narrow bandwidth frequency. The study is focused on the design of a diode structure for a coaxial vircator suitable for Chundoong IREB pulser (Max. 600 kV, 85 kA, 60 ns). It consists of a center annular cathode, a cylindrical meshed-anode and a reflector. The simulation results showed that the coaxial vircator can indeed be operated at the selected frequency with the narrow bandwidth and the microwave output power strongly depends on the position and geometry of the reflector. From this simulation results we expect that the maximum microwave output power will be obtained by the reflector of 4 cm in width and also 4 cm in distance away from the IREB, where the resonant frequency of microwave from coaxial vircator is simulated to be 6.577 GHz.