| In recent years,terahertz technology has gradually become a research hotspot in many fields.Compared with microwaves,terahertz waves have a larger bandwidth,so they have greater application potential in large-capacity communication systems.In addition,terahertz waves also have broad application prospects in the fields of human security inspection,material identification,and high-resolution imaging due to their short wavelength,low photon energy,and characteristic fingerprint spectrum.In terahertz system communication,the terahertz wave antenna determines the core parameters of the system,such as channel capacity,transmission distance,and efficiency.At present,the antennas mainly include parabolic antennas,dielectric lens antennas,and phased array antennas.Due to the short wavelength of the terahertz wave,the size of the antenna in the terahertz band is relatively small,and the accuracy of the curved antenna is difficult to guarantee,which makes its fabrication very difficult;at the same time,the limitation of the antenna size makes the wiring of the phased array antenna very difficult.In addition,since the transmit power of the current terahertz wave transmitter is generally not high,the antenna efficiency of the terahertz beam steering antenna is also very important.Higher antenna efficiency helps improve the stability and robustness of the overall system.Therefore,the research of high-efficiency passive planar antennas in the terahertz band has become a difficult problem to be solved urgently.In response to the above problems,this thesis focuses on the theme of "high-efficiency planar beam steering antenna for terahertz waves",and the main contents are as follows:(1)A transmissive terahertz beam steering antenna with a center frequency of 0.1THz is designed,and its beam steering angle can reach ±30 °.The antenna consists of two layers of planar metasurface deflectors.By optimizing the metasurface unit,the absolute bandwidth of the metasurface unit reaches 9.5 GHz,the relative bandwidth reaches 9.5 %,and the gain of the metasurface unit in the frequency band can reach-1.5 d B.The efficiency of the metasurface formed by this metasurface unit can reach more than 80 %,and the overall antenna efficiency can reach 61 %.(2)In order to improve the antenna efficiency,a high-efficiency reflective terahertz wave deflection device is designed.Since reflective metasurfaces have naturally high reflection efficiency relative to transmissive metasurfaces,the design of reflective metasurfaces is used.In addition,through the impedance matching theory,the reflective metasurface is optimized to further improve the reflection efficiency.The metasurface optimized for impedance matching achieves a reflection efficiency of over 90 % at an operating frequency of 0.34 THz and a reflection angle of 27 °.Compared with metasurfaces with linear phase gradients that are not optimized for impedance matching,the reflection efficiency is nearly doubled.Afterwards,in order to verify the practicability of this design,two kinds of metasurfaces,optimized and unoptimized,were prepared by combining electron beam evaporation coating process with photolithography and lift-off process for comparison.The experimental results show that the efficiency of the reflective metasurface optimized by impedance matching reaches 58.29 %.While the efficiency of the linear gradient metasurface without impedance matching optimization is 10.06 %,the efficiency of the optimized reflective metasurface is 4.7 times higher.Finally,the reasons for the error between the design and the experiment are analyzed. |
PDF Full Text Request