ANALYSIS OF RECTANGULAR WAVEGUIDE GRATING SLOW-WAVE STRUCTURE WITH THE ARBITRARY SHAPED GROOVES
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ANALYSIS OF RECTANGULAR WAVEGUIDE GRATING SLOW-WAVE STRUCTURE WITH THE ARBITRARY SHAPED GROOVES Zhigang Lu, Yubin Gong, Yanyu Wei, Yu Huang and Wenxiang Wang National Key Laboratory of High Power Vacuum Electronics University of Electronic Science and Technology of China Chengdu, China, 610054 Received 1 January 2006 Abstract: The rectangular waveguide grating slow-wave structure (SWS) with arbitrary shaped grooves is presented and analyzed in this paper. As an all-metal slow-wave circuit, it has properties that can be used in high-power millimeter-wave or sub-millimeter wave traveling wave tube (TWT). The unified dispersion equation and the expression of coupling impedance are obtained in this paper by means of an approximate field-theory analysis, in which the profile of the groove is approximately replaced by a series of steps and the field continuity at the interface of two neighboring steps together with the field matching conditions at the interface between the groove region and the interaction region are employed. A rectangular groove SWS was manufactured and the cold measurement was made. The experimental data are in good agreement with the numerical calculation. The derived transcendental equations are resolved numerically for four classical structures such as rectangular, dovetail, ladder and cosine. Finally, taking the rectangular waveguide grating SWS with rectangular grooves for example, the influences of physical dimensions on dispersion relation and coupling impedance are discussed. 791
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Key words: TWT, rectangular waveguide grating, millimeter-wave traveling wave tube, SWS, arbitrary shape 1.
Introduction Recently, a new need for high-frequency, high-power sources has been
emerging for advanced radar and communication needs, with frequencies in the band between 100 and 300GHz and peak powers as high as several hundreds of kilowatts, and with bandwidth of up to 10%. After investigation of the interaction mechanisms of different slow-wave structures, the rectangular waveguide grating SWS [1] has attracted the scholar’s interest due to some of its peculiarities: the scalability to smaller dimensions and shorter wavelengths, high precession of manufacturing and assembling, super thermal conductivity and low loss, which make it worth consideration, especially at millimeter-wave frequency-band. The investigation on rectangular waveguide grating SWS [2] with the rectangular grooves shows that this structure is intensively dispersive when it operates at the foreword wave region, which is only suitable for use in the narrow-band millimeter wave communication TWT. According to the experiences that the predecessors have obtained from the research on different slow-wave structures [3]-[6], it is indicated that variation of the groove shape can intensively impact and improve dispersion characteristics. For both analyzing practical circuit such as the deformed structures, etc., and obtaining a better dispersion circuit, it is necessary to consider the influence of the groove forms, such as V-typ
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