Electromagnetic Mode Transformation Structure Based On Metamaterial

In recent years,with the development of millimeter wave and terahertz technologies,more and more applications require high-power millimeter wave-terahertz radiation sources.Traditional microwave slow-wave devices work in fundamental mode and operate in the millimeter wave and terahertz frequency bands.The high-frequency structure has a small size,low power density,difficult processing,and high cost,and is difficult to be applied on a large scale.Therefore,microwave devices operating in higher-order mode are gaining more and more attention from researchers.Gyrotrons,photonic crystal klystrons,and high-order mode return wave tubes have been proposed and widely studied.However,the high-order waveguide mode cannot be transmitted in free space and is difficult to apply directly,so it needs to be converted into a mode or converted into a fundamental mode or a Gaussian beam.Metamaterial is an emerging electromagnetic material in recent years.It refers to an artificial composite structure constructed using artificial engineering methods.The properties are determined by the geometric structure rather than the chemical composition of the material.This structure has no common natural materials.The super-normal characteristics have the electromagnetic characteristics that natural materials do not have.When electromagnetic waves propagate in artificial metamaterials,they will exhibit characteristics different from those propagating in ordinary materials,so it is expected to achieve the conversion of higher-order waveguide modes into Gaussian beams.Based on the design principles of artificial metamaterials and the differences in the electromagnetic characteristics of the waveguide mode and Gaussian beam,this paper explores the electromagnetic mode conversion structure based on artificial metamaterials.A 35GHz circular waveguide TE₀₁ mode to Gaussian beam and a circular waveguide TE21 mode to Gaussian beam mode converter based on the"+"cell structure are designed.The simulation software is used to simulate the cell structure.According to the characteristics of whether the phase shift curve is gentle and whether the amount of phase shift is large enough,the appropriate number of cell layers and layer spacing are determined.The total size is determined according to the frequency,and the thickness and material of the metal and the thickness and material of the dielectric substrate are determined according to the actual processing conditions.The electromagnetic simulation results show that the Gaussian purity of the transmitted field achieves good results.The TE₀₁ mode converter was processed and tested.The power probe is used in conjunction with the stage to perform a surface scan test on the transmitted electric field of the completed TE₀₁ mode converter.The experimental test results from 35GHz to38GHz are consistent with the simulation results,which further proves that the mode converter design described in this paper is effective and feasible.