PULSED FERRITE X-BAND GENERATOR
STANFORD UNIV CA MICROWAVE LAB
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A magnetically saturated ferrite subjected to a pulsed magnetic field forms a generator of coherent microwave energy. It is shown that relatively high peak rf power in short pulses can be generated in this way. A pulsed magnetic field having amplitude approximately 4 Kg and rise time approximately 1 ns is developed by a strip-line pulser with spark-gap switches. This pulsed field causes nonadiabatic excitation of a coherent oscillation in a YIG sphere. The pulsed field also produces adiabatic pumping of the frequency and energy of this oscillation, so that the output frequency is not related to the pulsed- field rise time. The entire process is completed inside the build-up time of second-order spin waves, allowing precession angles in the YIG to exceed the usual steady-state spin-wave threshold by an order of magnitude. A monolithic circuit element contains a pulsed-field loop and an x-band resonator, which are mutually uncoupled but both tightly coupled to the YIG. The resonator extracts x-band energy from the YIG by radiation damping and transfers it to an output waveguide. The resonator is tunable and determines the output frequency. Coherent, nearly monochromatic rf output pulses having energy of several hundred watt-ns, and pulse widths in the range of 1 - 3 ns, have been observed using YIG diameters in the vicinity of 50 mils. These results are in good agreement with theoretical predictions.
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