Research On High-directivity Holographic Metasurface

As a new type of artificial electromagnetic metasurface,the holographic artificial impedance modulation surface draws on the principle of optical holography in its design concepts.The current generated by the feed antenna excites the interference pattern with impedance information distributed,and the impedance modulation is utilized to radiate leakage waves or bind surface waves.The holographic metasurface is usually composed of a series of subwavelength cells arranged in a two-dimensional quasi-periodic laws.The physical and geometric size of these cells can be continuously changed,which can not only achieve the purpose of accurate regulation of electromagnetic waves,but also have the ability to form high gain and narrow beam width.In addition,the feed antennda and the holographic metasurface are printe on the same profiles,making the holographic metasurface antenna extremely low-profile and easy to conform to complex objects,which greatly improves its applicability in practical application scenarios.Therefore,this thesis takes holographic metasurface as the research object and makes a more in-depth study on the realization of high directivity of the antenna.The main contents and work as follows:1.The working mechanism of the holographic metasurface antenna is described,and the detailed formula of the antenna design principle is deduced.Based on the impedance cell model for realizing holographic metasurface antenna,the process of extracting its surface impedance using transverse resonance method and eigenmode simulation method is introduced in detail,and the surface impedance of the designed cell is extracted based on eigenmode simulation method that laid the foundation for the design of the subsequent antennas.2.The high-directivity multi-beam antennas based on holographic metasurface are studied.Firstly,the forward and backward radiation patterns of the leaky wave are introduced in detail and based on these two radiation patterns,the design of the dual beam antenna in subregion is implemented which realized the directional radiation of the energy of the monopole antenna.Subsequently,the principle of field interference superposition is introduced into the design of holographic metasurface antennas and realized the dual-beam and four-beam antennas under the combination of the two radiation modes,compared with the separate control method by region,the metasurface aperture is reduced by half and a relatively high directivity is guaranteed.Finally,we achieve the design of six-beam antenna based on three ways that these all can achieve the directional radiation of monopole energy,while the comparison indicates that the introduction of field interference superposition principle makes the multi-beam antenna more directional.3.The end-fire antennas based on holographic metasurface are studied.Firstly,we designed a planar end-fire antenna that the introduction of the holographic metasurface increases the gain of the monopole antenna in the end-fire direction by 8.1 dB.Subsequently,through the correct theoretical derivation of surface waves and radiated waves on a conformal curved surface,a conformal end-fire antenna is designed to achieve a highly directional radiation in the end-fire direction when the surface waves encounter with the curved protrusion.And based on the omnidirectional radiation characteristics of the monopole antenna,these two single beam antennas are expanded into four beam radiation antennas.In addition,for the planar end-fired antennas,we replace the surface wave feed that reduces the profile of the antenna and the maximum gain in the endfire direction is increased by 1.5 dB under the same aperture metasurface,in the meanwhile,the antenna sidelobe is reduced.For conformal endfire antennas,we replace the surface wave feed that achieve 0.7 dB gain improvement with less cells.