LOW NOISE MICROWAVE AMPLIFICATION,
JOHNS HOPKINS UNIV SILVER SPRING MD APPLIED PHYSICS LAB
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The outstanding characteristic of the maser as a microwave amplifier is its inherently low noise. The measurable noise temperature of 10-20K indicates that the maser is operating at the theoretical limit of 1-2K. With no restrictions on the magnet size there appears to be no limit to the operating frequency range. Potential power handling capabilities of milliwatts tuned over hundreds of megacycles should make this an ultimate low-noise amplifier. Both the pulsed and multi-level continuous systems will be greatly improved thru the use of new maser materials. The PN function parametric amplifiers requiring little or no cooling and no magnetic field have shown almost comparable performance below 1000 Mc. For frequencies above 6-7 KMc, however, the design of the functions will have to be vastly improved. Ultimately, the limit will be set by the incompatibility between the barrier capacitance and the spreading resistance both of which should be minimal for increasing figure of merit. The garets and ferrites may then play an intermediate role in spite of the relatively large pumping powers, since there appears to be no frequency limitation and extreme cooling is not required. In all types of operation the use of traveling wave structures is expected to allow markedly improved performance. The parametric beam tubes, electron beams with mixed properties and the improved low noise conventional TW and BW tubes should find rapid acceptance if the low noise features can be scaled to the higher frequencies.
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