Theoretical Research And Design Of Holographic Antenna

With the deepening of information technology in modern society,wireless communication has been widely used in various fields of life and work.The antenna used to realize the function of detection and location is the key of wireless communication system.The excellent performance of the antenna directly determines whether the information can be transmitted in time and effectively.Therefore,make the antenna have higher gain,better directionality,stable performance and easy integration with other devices has become the focus of antenna designers.Holographic antenna is different from conventional antenna and antenna array in design and implementation.Holographic antenna features the characteristics of low profile and flexible construction.The feed structure of holographic antenna is easy to design.Holographic antenna can achieve radiation beams with high gain and high directionality.With the continuous improvement of the requirements of modern wireless communication system,it also brings more severe challenges to the antenna design.The research of holographic antenna intersects with the related concepts of microwave lens,reflector antennas,microwave metamaterial and electromagnetic modulation.And this can bring more possibility and innovation to the design of antenna.The design idea of holographic antenna comes from the field of optics,which is suitable for the development of millimeter wave,submillimeter wave and THz.The emergence of new materials and new technology also brings new vitality to the development of holographic antenna.The goal of this dissertation is to improve the performance of holographic antenna.The research contents of this dissertation focus on the improvement of the holographic antenna feed,gain enhancement,modulation method improvement,wavelength multiplexing and so on.On the basis of relevant theories,some innovative research studies are made in this dissertation.The research work of this dissertation mainly includes the following aspects:1.The design method of plane lens is studied in this dissertation.Surface wave launcher(SWL)is a common type of feed in the design of strip holographic antenna and it can produce cylindrical surface wave with good performance.In order to further improve the feed performance of strip holographic antenna,a planar lens is designed based on the periodic subwavelength element structure.Cylindrical surface waves produced by surface wave launche can be transformed into uniform plane waves by the proposed lens.In this dissertation,the proposed lens is applied to the design of strip holographic antenna.The experimental results show that the radiation performance of the antenna is greatly improved,and the beam gain is increased by 5 d B.On this basis,a novel type of "strip combination" element structure is presented and applied to the design of plane lens in this dissertation.The proposed novel element structure can adjust and control the electromagnetic wave front more flexibly.2.The method of increasing the gain of strip holographic antenna is studied,and an array feed structure is proposed in this dissertation.Huygens principle points out that infinite point sources with the same phase and amplitude can be superposed each other to form perfect uniform plane wave in theory.Based on this theory,the surface wave launcher is used as a point source and four surface wave launchers are combined to form an array feed to generate uniform plane wave.The leaky wave radiation is realized by using the strip holographic structure.The experimental results show that compared with the design method of using single surface wave launcher as the feed,the main beam gain of the holographic antenna with array feed is increased by 6 d B.3.In the antenna designed in 2,theoretically the electric field should be sinusoidally distributed along the strip direction(the direction in which the wave is not modulated).However,because the length of straight strips is not infinite,reflection of electromagnetic wave is produced in the truncated part of the dielectric substrate.As a result,the sinusoidal distribution of the electric field along the strip direction is affected,and the radiation performance of the antenna is decreased.Thus,a short-pin modulation method is predented in this dissertation.The distribution of electric field is improved by adding short-pin along the strip direction and the radiation performance of antenna can be improved.The experimental results show that the main beam gain of the holographic antenna is further increased by 1.9 d B,and the sidelobe level can be effectively reduced.4.The multibeam design method of holographic antenna is studied in this dissertation.The artificial electromagnetic surface has a flexible modulation effect on electromagnetic wave.As one of the applications of artificial electromagnetic surface,impedance modulation surface plays an important role in the design of holographic antenna.In this dissertation,a gain controlled four beam holographic antenna based on impedance modulation surface is designed.The gain of each beam can be controlled independently by tuning the amplitude coefficient of each beam.Besides,the frequency sweep characteristics of the holographic antenna are analyzed,and the frequency sweep angle range of the designed four beam holographic antenna is given.5.The wavelength multiplexing design method of holographic antenna is studied in this dissertation.Holographic antenna has frequency sweep characteristics.Therefore,for the traditional design,it is difficult to achieve the same beam angle radiation at different frequencies by using one single holographic antenna.Under this background,this dissertation focuses on wavelength multiplexing holographic technology.Firstly,four holographic beams with different frequencies and the same beam angle are recorded on the same holographic surface by using the direct modulation method.Due to the mutual coupling of different beam modulation,the radiation performance of the holographic antenna is seriously affected.Thus,this dissertation presents a modified modulation method based on region division.The whole holographic surface is divided into four regions,and double wavelength impedance modulation is carried out in each region.This modified method not only ensures the maximum modulation area of each beam,but also reduces the coupling effect between different beam modulation.The radiation performance of the whole antenna is greatly improved,and finally four wavelength holographic multiplexing is realized.The proposed holographic antenna exhibits the same beam angle at four different frequencies of 17 GHz,18 GHz,19 GHz and 20 GHz.