A traveling-wave maser system for radio astronomy

The design of a traveling-wave maser (TWM) for radio astronomy is discussed with particular reference to the Onsala system, which at present includes eight masers covering most of the frequency range 1-8 GHz (the frequency range in which the telescope is useful). Data are presented on the maser crystals iron- and chromium-doped rutile. A short discussion of different types of slow-wave structures (SWS´s) used as maser interaction circuits, and some design criteria are given. We briefly consider the design of the ferrimagnetic isolator. A new method for rapidly retuning the maser to within a frequency band of the order of 100 MHz is introduced. The cryogenic system and the low-noise front-end waveguide are discussed. Also some general conclusions about the TWM bandwidth and a short survey of masers for frequencies above 10 GHz are given. Finally, we discuss which types of radio-astronomical research programs could most benefit from these extremely low-noise amplifiers.