Improved multiple-cavity ruby masers are under development for use as low-noise amplifiers (LNAs) for receiving very weak radio signals in frequency bands up to and including one centered approximately at 32 GHz. These masers were designed specifically to be incorporated into receivers in ground stations of NASA’s Deep Space Network. The design may be useful in terrestrial cellular telephone terminals where high selectivity and immunity to the generation of intermodulation products may be needed.

The designs simplify field operations, afford high reliability, minimize required pump power levels, and provide noise temperatures near quantum limits. The low pump-power requirements enable operation in commercially available closed-cycle helium refrigerators at temperatures of ≤4 K. Another important aspect of the designs is small size, enabling the placement of many amplifiers in a single refrigerator in support of arrayed feeds, operation at multiple frequencies, and/or simultaneous dual-polarization operation, some or all of which are needed in many receiving systems.

A maser of this type includes a ruby-filled cavity, one or more signal-coupling cavities, one or more pump-coupling cavities, and a pump-reject filter, all combined in a single amplifier assembly. Signals are routed to and from the amplifier assembly via a transmission line (which is a waveguide in the case of 32 GHz) connected to a circulator. At 32 GHz, the amplifiers are small enough that twelve of them can fit within a single solenoid that has an inner diameter of 10 cm.

Each amplifying cavity is a half-wavelength waveguide resonator filled with ruby (having dimensions of 2.601 by 1.3005 by 1.016 mm in the 32-GHz case). The pump-reject filter is located in a waveguide, called the “signal waveguide,” between the ruby and the circulator. This filter reflects the pump energy that has passed through the ruby back to the ruby, thereby confining the pump energy to the amplifier in order to maximize the pumping efficiency.

The tuning range of the 32-GHz version covers the deep-space-to-Earth frequency allocation of 31.8 GHz to 32.3 GHz with an instantaneous bandwidth of at least 100 MHz and an amplifier noise temperature of 3.1 K. Slightly lower noise temperature may be possible when this maser is operated in a refrigerator at a physical temperature <2.2 K.

This work was done by James Shell and Robert Clauss of Caltech for NASA’s Jet Propulsion Laboratory. For further information, access the Technical Support Package (TSP) free on-line at www.nasatech.com/tsp  under the Electronic Components and Systems category.

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to

Intellectual Property group
JPL
Mail Stop 202-233
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(818) 354-2240

Refer to NPO-30143, volume and number of this NASA Tech Briefs issue, and the page number.