S-band Metamaterial Backward-wave Oscillator

Metamaterial is a kind of artificial structure with special electromagnetic properties,which has exotic properties different from conventional materials,such as negative refractive index,reversed Doppler effect,reversed Cherenkov radiation and abnormal light pressure characteristics.Since the birth of metamaterial,great technological changes have taken place in national defense,information technology and communications.Many new technologies have been realized based on the birth of metamaterial,and new potentials have been tapped from metamaterial.The existing vacuum devices based on metamaterial have many advantages,such as high power,high efficiency,but the characteristics of large volume and high operating voltage also restrict the development and production of microwave vacuum devices.The work of this paper is to optimize the large volume and high voltage metamaterial backward-wave oscillator,reduce the operating voltage,reduce the device size,and ensure its high output power and electronic efficiency.The main work of this paper is as follows:1.The transmission characteristics of a structure unit are simulated by CST simulation software,and the constitutive parameters of the structure unit are extracted by parameter extraction method,thus the negative dielectric constant of the structure is verified.In order to make the structure possess negative permeability,it is combined with metal hollow waveguide to make the whole structure possess double negative characteristics,which proves theoretically that the structure conforms to the definition of metamaterial.2.Based on this metamaterial,a slow wave structure is designed and its high frequency characteristics are simulated.The simulation results show that the slow-wave structure can transmit the backward wave,which conforms to the working principle of the backward-wave oscillator.Simultaneously,it has high coupling impedance and the ability of beam-wave interaction.3.The period number and length of the slow-wave structure are optimized,and the metamaterials are arranged in a uniform periodic manner.Based on this,a S-band backward-wave oscillator with coaxial electro-coupled probe output is designed.The length of the backward-wave oscillator is only 115 mm.Compared with the conventional backward-wave oscillator,it has obvious advantages of miniaturization.The simulation calculation and experimental verification of the transmission characteristics and the simulation calculation of the beam-wave interaction are carried out.The calculated results show that the frequency of the signal is stable at 2.214 GHz,which meets the requirements of S-band devices.At the same time,the maximum output power can reach 18 kW.Through calculation,we can know that its efficiency is about 28.9%.Compared with the conventional backward wave oscillator,it has been greatly improved.4.Phase velocity jump technology is used to optimize the number and length of periods of slow-wave structures.Based on this,an S-band backward-wave oscillator with coaxial magnetic coupling ring is also designed.The simulation calculation and experiment of its transmission characteristics are carried out and the beam-wave interaction is simulated.The results show that the peak power can reach 26 kW and the electronic efficiency increases to 29.4%.Although the volume is slightly increased,the output power and electronic efficiency are improved.