D.N. Zolotykh - Ph. D. (Eng.), Head of Sector, JSC «SPE «Almaz» (Saratov) E-mail: zolotyhdn@almaz-rpe.ru V.I. Rogovin - Ph. D. (Phys.-Math.), Associate Professor, Deputy Director of JSC «SPE «Almaz» (Saratov) E-mail: rogovinvi@almaz-rpe.ru

One of the perspective directions of microwave electronics development is designing the broadband vacuum amplifiers in THz-frequency band. In the article, the results of implementation of the slow-wave structure of TWT amplifier intended for operation in the band of 0.2 THz are presented. The slow-wave structure of the «comb»-type is a sequence of «ridges» arranged with a period of 100 µm on a metal plate. The proposed slow-wave structure is designed to work with five cylindrical electron beams. Semi-cylindrical grooves are made in the «ridges» of the slow-wave structure to improve the efficiency of interaction between the electron beam and electromagnetic wave. The grooves and the electron flows are arranged equidistantly. Central electron beam interacts most effectively with the field of slow-wave structure. Electrodynamic characteristics of slow-wave structure were determined using the software «HFSS». The analysis of electrodynamic characteristics of the proposed slow-wave structure was carried out over the frequency range from 171 to 199 GHz. It is shown that at the frequency of 194 GHz interaction impedance value defined on the symmetry axis of the electron beam is 5 Ohms for the central electron beam, 1 Ohm for outer electron beams and 2.5 Ohms for electron beams, located between the central and outer electron beams. The value of the distributed attenuation at this frequency is approximately 3 dB/cm. The TWT based on the presented slow-wave structure was calculated. The interaction space of the designed TWT has not local attenuators. The optimal TWT accelerating voltage is 15 kV at the frequency of 194 GHz. Each of the five electron beams provides a current approximately equal to 30 mA. The electrical length of the TWT is equal to 7.5. Output power of TWT was calculated by the program based on the nonlinear theory of interaction between the electron beam and the longitudinal component of the electric field of slow-wave structure in one-dimensional approximation. The calculation was performed assuming that the electron beams do not interact with each other through the fields of space charge. It was considered two approaches to the calculation of five-beam TWT. The first approach was to replace the five electron beams by the one equivalent beam for which the interaction impedance was calculated as the mean value for all electron beams at the operating frequency. The current of equivalent electron beam was calculated as the algebraic sum of the partial electron beams currents. The interaction impedance was calculated as the mean value for all beams at the operating frequency of 194 GHz. The value of electronic efficiency of TWT is more than 3% at the gain value of 35 dB and output power of 35 W. Another approach was to calculate TWT output power considering the interaction with an individual electron beam. In this case, the TWT output power was not more than 32 W.

 

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