Helically corrugated waveguides for compression of frequency swept microwave pulses

MacInnes, P. and Cross, A. W. and Ronald, K. and Phelps, A. D. R. and He, W. and Burt, G. and Young, A. R. and Whyte, C. G. and Samsonov, S. V. and Denisov, G. G. and Bratman, V. L.; De Marco, F. and Vlad, G., eds. (2006) Helically corrugated waveguides for compression of frequency swept microwave pulses. In: 33rd EPS Conference on Plasma Physics 2006, EPS 2006 - Europhysics Conference Abstracts. 33rd EPS Conference on Plasma Physics 2006, EPS 2006, 301 . European Physical Society (EPS), ITA, pp. 2316-2319. ISBN 9781622763337

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Abstract

Short pulse high power microwave radiation can be used for time of flight diagnostic measurements in plasmas, e.g. density profiles by reflectometry. A three-fold helical corrugation of the inner surface of a waveguide synthesises eigenwaves having useful dispersive properties by combining two distinct counter-rotating modes of a corresponding circular waveguide. The dispersion may be tailored to the requirements of an application by adjusting the amplitude and period of the corrugations. Such dispersive properties have proven useful in broadband radiation amplifiers, or to achieve passive compression of smoothly frequency modulated microwave pulses. The paper presents results of experiments using a solid state source to produce an optimised frequency-chirped input pulse and amplified by a high power Travelling Wave Tube Amplifier (TWTA). The waveforms of the input and output microwave signals were captured on a UHF Digital Storage Oscilloscope. The results demonstrated at 5.7kW input power levels that X-band radiation pulses of 67ns duration with 5% frequency modulation can be compressed into a 2.8ns pulse having 12 times higher peak power, whilst retaining 50% of the energy in the input signal. The technique offers great potential for scaling to higher frequencies and power levels.

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