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Powerful millimeter range TWT with precision manufacturing technology matching design elements

DOI 10.18127/j00338486-201907(10)-14

Keywords:

A.V. Galdetskiy – Ph.D. in Radiophysics, Head of Department, JSC «RPC «Istok» named after Shokin» (Fryazino)
E-mail: galdetskiy@istokmw.ru
E.A. Bogomolova – Leading Engineer, JSC «RPC «Istok» named after Shokin» (Fryazino)
E-mail: yaea89@inbox.ru
L.A. Saprinskaya – Leading Engineer, JSC «RPC «Istok» named after Shokin» (Fryazino)
I.M. Sokolova – Leading Engineer, JSC «RPC «Istok» named after Shokin» (Fryazino)
I.P. Natyra – Leading Engineer, JSC «RPC «Istok» named after Shokin» (Fryazino)
A.I. Korchagin – Ph.D.(Eng.), Leading Research Scientist, NIKA-Microwave, Ltd (Saratov)
E-mail: korchagin_aleksey@mail.ru


Designs of slow wave structure (SWS), input-output matching circuits, electron-optics and magnetic system for W-band TWT are proposed and simulated. Analysis of dispersion of SWS shows that bandwidth 1 GHz can be achieved by introducing special inductive elements in conventional folded waveguide in the form of shortcircuited waveguides. Moreover, additional ferrules are set in the design for increasing of interaction impedance. Such SWS «modified folded waveguide» possesses weak dispersion and enhanced interaction impedance making possible design of TWT with extended bandwidth. Analysis of beam interaction with travelling wave is conducted using proprietary 2D-software taking in account influence of space charge and nonlinear effects. Electron beam is focused in channel by PPM system having first harmonics amplitude B = 0.39 Tl and pitch 9.6 mm. Electron beam is not intercepted, filling factor at the channel output is equal to 0.85. Asymmetric single-stage depressed collector is employed at voltage 8.5 kV. Calculated collector efficiency achieves 52%, maximal dissipated power density is 475 W/cm2. Design and dimensions of TWT provide operation of TWT in CW and pulse mode. Novel design of sever uses absorbing ceramics AN-MKH2 having ε = 22 and tgδ = 0,16. Fixed thickness of ceramics wafer provides good heat removing, and tapered form of ceramic wafer can be easily realized by laser cutting. At wafer length 5 mm reflection coefficient doesn’t exceed −30 dB ensuring stable operation of TWT. Simulation shows that sever properties have small dependence on dielectric parameters of ceramics. Problems of precise fabrication of SWS and matching components are considered. We proposed fabrication of all elements of SWS and output waveguides in single cutting process with subsequent bonding. Designs of input and output matching circuits are simulated. Calculated VSWR of matching circuit and vacuum window doesn’t exceed 1,07 in frequency band 1 GHz. Considered design of TWT with SWS «modified folded waveguide» should ensure operation with CW output power exceeding 60 W and gain 42 dB in bandwidth 1 GHz at beam current 94 mA and voltage 17.5 kV.

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