Research On Millimeter-wave Terahertz Quasi-Optical Mode Converter

Millimeter-wave and terahertz wave technology is a rapidly developing frontier field with important application prospects and research values.The quasi-optical mode converter is widely used for millimeter-wave and terahertz wave generation,transmission,regulation and reception emission,and is an essential component of millimeter-wave and terahertz application systems.With the goal of developing a novel quasi-optical mode converter,the comprehensive theoretical analysis,numerical simulation and experimental study of quasi-optical mode converters based on optical mirrors and artificial electromagnetic metamaterials,are carried out in this dissertation.The main research contents include the following aspects:1.Theoretical investigations was conducted on the quasi-optical transmission characteristics.Based on the geometric optics theory,the mirror equations of the elliptical cylindrical mirror and parabolic cylindrical mirror of the Vlasov-type quasi-optical mode converter are derived.A 220 GHz Vlasov-type quasi-optical mode converter is designed by combining the vector diffraction theory.Aiming at the problem of long-distance transmission divergence of the output beam of the traditional quasi-optical mode converter,a Cassegrain antenna structure is proposed to collimate the output Gaussian beam and reduce the beam divergence angle.Based on the geometrical optics and the vector diffraction theory,a numerical program is written to calculate and optimize the structural parameters of each mirror,and the results are compared with those of commercial electromagnetic simulation software.2.An novel quasi-optical mode converter based on artificial metamaterials was carried out.Aiming at the problems of low power capacity and large metal ohmic loss of traditional metal-dielectric metamaterials,dissertation investigates a new quasi-optical mode converter based on all-dielectric metamaterials.The all-dielectric metamaterial has the advantages of high-power capacity and low loss,which can realize the polarization conversion of plane waves.On this basis,four all-dielectric metamaterial quasi-optical mode converters with different input modes are designed for converting circular waveguide TE₀₁,TE₂₁,TE₃₁,and TM₀₁ modes to linearly polarized Gaussian modes.At the operating frequency of 35 GHz,the electromagnetic simulation results show that the output field scalar Gaussian mode content of all four novel quasi-optical mode converters exceeds 94%and have high single linear polarization purity.3.Four terahertz circularly polarized quasi-optical mode converter array structures are studied to convert 0.35 THz circular waveguide TE₀₁ modes into linear polarized（LP）,left-hand circularly polarized（LHCP）,right-hand circularly polarized（RHCP）and dual circularly polarized（DCP）Gaussian beams,respectively.The electromagnetic simulation results show that the scalar Gaussian mode content of the corresponding LP,LHCP,RHCP and DCP output waves is above 98%,and the LHCP and RHCP Gaussian beams can be generated simultaneously in the dual circular polarization converter.4.The validation experiments of the all-dielectric metamaterial quasi-optical mode converter were carried out,a Lab VIEW-based automated two-dimensional radiation field measurement system was built,and the all-dielectric metamaterial quasi-optical mode converter of circular waveguide TE₀₁ mode was processed and tested.The experimental results show that the quasi-optical mode converter successfully converts the circular waveguide TE₀₁ mode into a single LP quasi-Gaussian mode at 35 GHz operating frequency.The measured scalar Gaussian contents are larger than 90%in the frequency range from 30 GHz to 38.85 GHz,suggesting relative bandwidth of 25.3%to the center frequency 35 GHz.The experimental results are consistent with the design simulation results.