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Kesari V.,Microwave Tube Research and Development Center | Keshari J.P.,Galgotias University
IEEE Transactions on Plasma Science | Year: 2013

An additional disk was introduced in the unit cell of a periodic disk-loaded interaction structure for a gyro-traveling-wave tube, and the small-signal gain-frequency response of the device was studied. The dispersion data of interwoven-disk-loaded structure were fed into the small-signal gain equation for the calculation of the small-signal device gain. The effects of the gyrating electron beam, magnetic field, and dimensional parameters were discussed in order to achieve a wideband device performance. The gain-frequency response of an interwoven-disk-loaded device was compared with that of a conventional disk-loaded device to show the widening of the device bandwidth. For typically chosen structure parameters, the 3-dB device bandwidth was found to be improved from 4.7 to 6.4 GHz (\sim36%) in a Ka-band device. © 1973-2012 IEEE. Source


Kesari V.,Microwave Tube Research and Development Center
IEEE Transactions on Plasma Science | Year: 2013

The performance of a disc-loaded gyro-traveling wave tube (gyro-TWT), which is optimized a priori by controlling the structure parameters for wide device bandwidths at large gains, is analyzed for studying the sensitivity of the gain and bandwidth of the device to the beam and the magnetic field parameters. Hence, it is predicted that the optimum beam and the magnetic field parameters will result in a much wider bandwidth at a larger gain than that of a smooth-wall gyro-TWT. © 1973-2012 IEEE. Source


Kesari V.,Microwave Tube Research and Development Center
Progress in Electromagnetics Research | Year: 2010

The electromagnetic field analysis of the disc-loaded-coaxial waveguide in two configurations was developed in TE-mode for its potential application in the fast-wave regime using the field matching technique at the cylindrical interface between disc-free and disc-occupied structure regions. The space harmonics were considered for the axial periodicity and the azimuthal harmonics were ignored for azimuthal symmetry of the present configurations. The dispersion and azimuthal interaction impedance characteristics obtained by present analysis were validated against those obtained by simulation software - HFSS within 0.1% and 0.5%, respectively. In special cases, the disc-loaded-coaxial structure reverts to well known conventional structures. The effect of structure parameters on the shape of dispersion characteristics was investigated in order to obtain a wideband-coalescence between the beam- and waveguide-mode dispersion characteristics, required for the wideband device performance, without deteriorating the azimuthal interaction impedance value. Source


Kesari V.,Microwave Tube Research and Development Center
IEEE Transactions on Electron Devices | Year: 2014

A composite circular waveguide interaction structure of a gyro-traveling-wave tube (gyro-TWT) consisting of azimuthally periodic alternate dielectric and metal vanes projecting radially inward from the waveguide wall was analyzed by the field matching technique considering the effect of azimuthal harmonics. The dispersion relation of the waveguide excited in the TE mode obtained by the analysis was validated against the simulation within 5% and then used to find the optimum structure parameters for wideband coalescence between the beam and the waveguide mode dispersion characteristics for wideband device performance. The dispersion data fed into the gyro-TWT gain formula established the superiority of the proposed composite dielectric-and metal-vane-loaded waveguide in providing a wide bandwidth of the device without much sacrifice of its gain while requiring a lower beam voltage and magnetic field, over a waveguide loaded by a dielectric lining alone or by metal vanes alone. © 2014 IEEE. Source


Kesari V.,Microwave Tube Research and Development Center | Keshari J.P.,Galgotias University
Progress In Electromagnetics Research M | Year: 2012

The shaping of dispersion characteristics in a variant of disc-loaded circular waveguide was studied through electromagnetic analysis for assessing the structure for wideband coalescence of the beam- and waveguide-mode dispersion characteristics that entails the wideband gyro-travelling-wave tube (gyro-TWT) performance. In this variant of disc-loaded circular waveguide, the alternate disc-hole radii were varying, however, the structure was periodic. The structure periodicity coupled with Floquet's theorem and field-matching technique resulted into the dispersion relation of the infinitely long structure. A numerical code was developed to solve the dispersion relation, and the dispersion characteristics of the structure were analyzed for the azimuthally symmetric TE-modes. The effects of structure parameters were studied for getting a straight-line portion of the dispersion characteristics over a wide frequency range. The dispersion shaping was projected for typically chosen TE 01-mode. The results were validated against those obtained for the conventional and un-conventional known structures and those obtained using commercially available simulation tool. The variation of azimuthal electric field intensity over the radial coordinate was also studied to examine the control of structure parameter for maxima-position, where the gyrating electron beam would be positioned for optimum beam- wave interaction in a gyro-TWT. Source

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