Research Of High Power Millimeter Wave Frequency Selective Surface And Its Application

Millimeter wave has both the advantages of all-weather operation of microwave and the wideband and high resolution of infrared wave.It enjoys a wide application in areas such as long-range radar,electronic countermeasures,electronic interference and etc.The gyro traveling wave tube has high peak power and high average power output in the millimeter band and other frequency bands.Therefore,more and more millimeter-wave radar systems use gyrotron as their high-power source.In order to transmit the power radiated from the gyrotron to the radar antenna system effectively,a high-power millimeter-wave transmission link should be constructed.In the transmission link system,electromagnetic waves need to complete frequency separation,polarization conversion and so on.Therefore,the research of high power millimeter wave frequency selective surface(FSS)and circular polarizer is of great significance.The FSS has a spatial filtering function.The structure can realize separation of electromagnetic wave with a high isolation.Therefore,the high-power millimeter-wave FSS can realize multiplexing function and improve the utilization of the link system as well.Compared with other polarized electromagnetic waves,circularly polarized waves have more advantages.The high power millimeter-wave circular polarizer based on FSS can realize the polarization conversion of the electromagnetic wave and separate waves at the same time.Thus,it helps saving the use of a high-power device and making the link system more compact.This paper starts with the analysis of theory of FSS and Floquet theorem.The frequency separation characteristics of an all-metal high-power millimeter-wave FSS has be deeply studied.What's more,a FSS worked for Q-band and K-band is designed,and the separation of waves with a high isolation was achieved.By studying the circularly polarized waves and the theory of FSS based circular polarizers,as well as the dispersion theory of rectangular waveguides,a high power millimeter-wave circular polarizer was designed.However,the axial ratio bandwidth of the simulated structure cannot meet the design requirements.Furthermore,in order to broaden the bandwidth of the axis ratio.According to the design method of multilayer cascaded filter in circuit design,a bandwidth optimization scheme of axial ratio for FSS based circular polarizer is proposed.A double-cascaded structure was opposed to widen the axial ratio bandwidth.Thus,the design requirements are reached.Then,the circular polarizer designed earlier were fabricated and tested.The test results agree with the previous simulated results very well.Finally,the theory of metal grating circular polarizer is studied in detail,and a single-layer grating circular polarizer is designed.At the same time,the polarizer employs a planar waveguide structure based on sinusoidal perturbation to improve the axial ratio bandwidth,and discusses the influence of the sine function with different cycles on the performance of axial ratio.Next,based on the mode matching method and the cascade scattering matrix theory,a double-layer cascaded grating polarizer is designed.The grating circular polarizer is designed based on two groups of planar waveguide with vertical alignment.The designed grating polarizer also has the characteristics of low cross polarization level and high transmission efficiency.