A S-band Metamaterial Backward-wave Amplifier

With the progress and development of science and technology,vacuum electronic devices are gradually developing in the direction of high power,high efficiency,wide frequency band and miniaturization.Scientists around the world are constantly exploring ways to improve the efficiency,power and frequency band of vacuum electronic devices,metamaterials are a breakthrough in recent years.Metamaterial is a sub-wavelength structure constructed by artificial methods,which has electromagnetic properties not found in natural materials,it indicates the direction of the development of vacuum electronic devices,and is in contrast to traditional vacuum.Compared with electronic devices,metamaterial vacuum electronic devices have the advantages of miniaturization,all-metal,high power,high efficiency,and easy processing.In recent years,vacuum electronic devices such as metamaterial klystrons and metamaterial backward-wave oscillators have emerged.The main work of this paper is to apply metamaterials to amplifiers,and finally design a metamaterial backward-wave amplifier with high efficiency and miniaturization.The main work of this article is as follows:1.First select a metamaterial structure-complementary electric split ring resonator?CeSRR?for periodic arrangement to form CeSRRs array,which has a negative effective dielectric constant in a certain frequency range;For TM mode,an empty metal circular waveguide operating below the cut-off frequency has negative effective permeability characteristics;therefore,the CeSRRs array is loaded into an empty metal circular waveguide to form a metamaterial slow wave structure with double negative characteristics in the operating frequency range of 2.1 Ghz-2.55 GHz.2.On the basis of designing the metamaterial slow-wave structure,a signal input-output structure-coaxial electrical probe was studied.Finally,a single-stage metamaterial backward-wave amplifier working in the S-band was designed.Then use the electromagnetic simulation software CST to simulate its transmission characteristics,in the 2.27GHz-2.60GHz frequency band,S₂₁ is basically stable within-3dB and the maximum is-0.3dB,the effective bandwidth is about 330MHz.Furthermore,two equal-period single-stage metamaterial backward-wave amplifiers are constructed into a metamaterial cascaded backward-wave amplifiers,when the operating voltage U=38kV,the operating current I=0.45A,and the input power is 1.6W,the output power is 3.0kW,electronic efficiency is 16.89%,gain is 31.6dB and the 3dB bandwidth is about 11MHz.Furthermore,the phase-speed jump method and other methods were used to optimize it,finally,a metamaterial cascaded backward-wave amplifier with output power of 5.1kW,electronic efficiency of 29.83%,gain of 34.98dB and 3dB bandwidth of 10MHz was obtained.3.The radius of the slow-wave structure of the metamaterial cascaded backward-wave amplifier is only 20mm,which is about 2/3 of the coupled-cavity TWT?30mm?in the same frequency band,and its longitudinal length?410mm?is equivalent to the traditional structure,so its volume is about 4/9 of the traditional structure.Secondly,the electronic efficiency of the metamaterial cascaded backward-wave amplifier with optimized transition period is 29.83%,which is higher than that of traditional S-band coupled cavity traveling wave tube?about 14%-24%?and helix traveling tube?10%-20%?,so the metamaterial slow wave structure has the characteristics of miniaturization and high efficiency.In addition,the slow wave structure of the metamaterial backward-wave amplifier is an all-metal structure,which has good heat dissipation and is easy to process.