Techniques Of High-performance Antennas Based On Electromagnetic Metasurface Structures

As one kind of metamaterials,electromagnetic metasurface structures have attracted significant interest due to their unique features of manipulating electromagnetic waves,which are not possessed by natural materials.Among them,artficial magnetic conductor(AMC)can reflect incident plane wave in phase at a specific frequency band.Generally,it not only can be used as the ground plane of antennas,but also direct radiation elements(called as metasurface antenna),which can break the limitations of designs of traditional antennas and bring huge changes or improvements for antennas in wireless communication systems.With the development of wireless communication technology,to satisfy the demand for high-performance and smart millimeter-wave system and mobile communication system,requirements of the antenna performance become higher and higher.High-directivity,multifunction,wideband,compact and wide-beam scanning antennas are becoming the development trend of modern microwave,millimeter wave antenna.Therefore,it has very high academic value and application value to do researches on novel electromagnetic metasurface structures and its applications in antennas for enhancing performances.To satisfy the requirements of antennas in modern wireless communication systems,aiming at the existing research limitations of characteristic analyses of electromagnetic metasurface structures and its applications in antennas,some in-depth researches have been conducted and concluded in this thesis.The novelty of this thesis and the main contents can be summarized as:1.Investigations on high-directivity antennas using non-periodic AMC structures:Aiming at sloving the difficulties on intergration of cylindrical reflector with strong refelection characteristics due to the three-dimensional configuration,the non-periodic AMC technique based on the theory of projection equivalence is presented.Accordingly,serveral novel planar reflectors are constructed,which can be equivalent to cylindrical metal reflectors with strong reflections to realize high-directivity antennas.Based on above analysis,the non-periodic technique is extendedly applied in dual-polarized antennas and then novel spherically-projected non-periodic planes are proposed accordingly to realize dual-polarized patch antennas with high efficiency and high isolation.The measured results demonstrate the high-efficiency and high-gain radiation performance of the proposed antennas using non-periodic AMC structures.These works provide great space of development for designs of high-directivity antennas.2.Polarization-reconfigurable and frequency-tunable antenna using the novel active AMC Structures: A novel active AMC structure with polarization-reconfigurable and frequency-tunable reflection characteristics is firstly proposed.Besides,the multifunctional working mechanism is ananlyzed and the design strategies are also summarized.By employing the proposed active AMC as a ground plane of a pair of linearly-polarized dipole antennas,a multi-functional antenna can be well designed with polarization reconfigurability and frequency-tuning capability,where three polarization states of right-/left-handed circular polarization(R/LHCP)and linear polarization(LP)can be switched respectively,and the operating frequency of each polarization can be flexibly tuned.Besides,the bandwidth under the CP states can be adjusted.Combined with a varactor-based singlelayer network,the multi-functional antenna with polarization reconfigurability and frequency-tuning capability is realized and demonstrated.These works provide a good guidance for the design of simple and novel multi-functional antenna,and provide technical reference for achieving the multi-function antennas using electromagnetic metasurface structures.3.The non-periodic multi-resonance metasurface technique and its applications in wideband metsaurface antennas: The non-periodic multi-resonance metasurface technique is proposed to broaden the bandwidth of metasurface antennas.Besides,the design strategies of multi-resonance metasurface structure are also summarized.Starting from the size,arrangement and shape of metasurface structure,three kinds of non-periodic metasurface structures with multi-resoannce features are respectively realized.When applied these three non-periodic multi-resonance metasurface structures as direct radiation elements,three designs of wideband multi-resonance metasurface antennas are realized.The measured results verify the wideband and multi-resonance features.These works provide great space of development for designs of wideband metasurface antennas,and provide technical reference for satisfying the demand of modern wireless communication system in large channel capacity.4.Miniaturized wideband planar antennas based on the capacitive-loaded metasurface techniques: Starting from the equivalent circuit of the conventional square metasurface structure,three different capacitive-loaded metasurface techniques are respectively proposed including inter-embedded capacitive loading,cross-layer capacitive loading,parallel-plate capacitive loading,which can both miniaturize the size of metasurface structures while maintain their wideband feature.By applying these capactive-loaded metasurface structures in antenna designs,several miniaturized metasurface antennas with large bandwidth are realized accordingly.The measured results demonstrate the wideband and miniaturized features.These works provide feasible solutions to realize compact wideband metasurface antennas,and provide great space of development for the designs of metasurface antenna arrays,indicating one promising candidate for applications in modern wideband wireless communication systems.5.Millimetre-wave metasurface phased array with wide beam scanning for 5G communication: To satifisy the requirement of beam scanning for 5G mobile communication system,the above capacitive-loaded metasurface technique is applied in the millimetre-wave metasurface antenna designs.Combining with low-temperature co-fired ceramics(LTCC)technology,a compact millimeter-wave metasurface antenna with wideband and low-profile features is realized.Furtherly,the compact metasurface antenna element is applied to form a 4×4 millimetre-wave antenna array,exhibiting a wide beam scanning angle.Besides,to achieve high isolation in a small spacing,the decoupling method of counteract path is adopted,and then a large scanning angle can be realized.This metasurafce array is firstly used to implement a phased array.These works provide some useful guidance for antenna designs in 5G millimeter-wave system.