Research On Millimeter Wave Terahertz Quasi-Optical Element Components

In recent years,MMW frequency band has been widely studied and applied in communication,target detection,guidance and space remote sensing.In recent years,the working frequency of electronic systems has been increasing,and the development and utilization of terahertz(300GHz-10THz)spectrum has become a hot topic.Terahertz technology has been widely used in radio astronomy.Terahertz(THZ)signal has better resolution than MMW because its wavelength is shorter.Quasi-optical technology uses electromagnetic wave to transmit MMW terahertz signal by means of beam propagation in space,which has the advantages of small loss,high withstand power,relatively low processing difficulty and multi-beam multi-polarization.Common quasi-optical elements include conventional optical elements and diffraction optical elements.Diffraction optical element is a kind of element(such as diffraction lens and Fresnel zone plate)designed based on the principle of optical diffraction.This kind of optical element is a kind of small,efficient and arrayed optical element completely different from the traditional manufacturing method.Terahertz focal plane array imaging is similar to optical imaging,which is different from mechanical scanning and phased-array imaging.High resolution images can be obtained,and real-time imaging can be realized without the influence of antenna scanning speed.There are three main parts in this research: twist reflector,Fresnel zone plate antenna and terahertz focal plane array imaging system.The function of the twist reflector is to rotate the polarization mode of the incident wave at 90o.In this paper,based on the polarization transformation theory and the design method of the cross-polarization twist reflector,the polarization twist reflector with a frequency of 90 GHz,an incidence angle range of(-10o,10o)and a bandwidth range of(86GHz,94GHz)can achieve better polarization twist performance,and the polarization twist performance is the best when the incidence is normal.The polarization twist reflector with frequency of 98 GHz,incidence angle range of(-17o,26o)and bandwidth range of(94GHz,102GHz)can achieve better polarization twist performance,and the polarization twist performance is the best when the incidence Angle is 20o.Fresnel zone plate is a quasi-optical diffraction focusing device.Based on the principle of constructive interference,the structure of Fresnel zone plate is designed.Firstly,the structure of Fresnel zone plate with plane waves at different angles focused at the same focus is obtained,and the focusing efficiency at the focus is discussed.Then,by using reverse thinking,the horn is placed at the focal point to illuminate the Fresnel zone plate with different structures,and the characteristics of the scanning antenna of Fresnel zone plate at 220 GHz frequency are further studied.Terahertz focal plane array imaging system is an important field of terahertz technology and has important application needs in both civilian and military fields.This paper introduces the basic theory and design method of focal plane array imaging system.Double reflector antennas and receiving array antennas with different arrays are designed respectively.After joint simulation,the coupling efficiency of different receiving arrays at different incident angles is analyzed and compared.All contents of this research subject shall be combined with various electromagnetic simulation software(such as CST,HFSS,COMSOL)for simulation calculation on the basis of theoretical analysis.