Research On Water-based Optically Transparent Antenna And Isolation Reconfigurable Array Antenna

Transparent antennas show important application prospects in future wireless communication systems.They can be applied into numerous transparent structures such as mirrors,windows,or displays.They can also be used in some wearable tools such as watches or glasses.Material is also an important point for transparent antenna design.Firstly,the cost of antenna and complexity of fabrication process depends on materials.Secondly,performances of antennas is greatly determined by material.Most importantly,the correct material must be selected to ensure the high transparency of transparent antennas.Many materials have been studied for transparent antenna design such as fluorine-doped tin oxide,indium-tin-oxide and indium-zinc-tin-oxide.However,these materials are not easily available,and the fabrication process is very complicated and costly.Glass is another good candidate for transparent antenna design,and it has been successfully used in dielectric resonator antennas.However,the ground supporting the glass dielectric resonator antennas is still metal,which cannot achieve true optical transparency of the entire antenna structure.Compared with other materials,water is a potential material for optically transparent antenna design.It has several characteristics such as high transparency,low cost,compactness of the antenna and easy processing.Therefore,some optically transparent antennas have been designed through water,but their transparency is still limited by the metallic floor.On the basis of theoretical analysis,multiple-input multiple-output(MIMO)technology can significantly improve performances of communication systems such as channel capacity,data rate,spectrum or energy efficiency,etc.But the assumption of theoretical analysis is the weak enough spatial correlation and mutual coupling between antennas.The operational frequency band of 5G base stations becomes wider and wider,the number of antenna elements arranged in base stations becomes more and more,but the space used for base stations design is more and more limited.Therefore,using multiple antennas in a limited space and maintaining high isolation in a wide operational frequency band is one of the major challenges for future multi-antenna systems.Many decoupling technologies have emerged such as decoupling networks,metamaterials decoupling technology or defected ground structures decoupling technology,etc.However,they are designed on the basis of single frequency or limited by their resonant characteristic,and the isolation only can be imporved in a narrow band.In order to solve the narrow decoupling bandwidth,structures of the aforementioned decoupling technologies are often designed as a combination of multiple different sizes,then multiple deep notches of isolation in the operational frequency band can be realized.However,it conflicts with the miniaturization trend of the communication system.Therefore,designing a miniaturized wideband array antenna with high isolation is still a major challenge in 5G base stations.In this paper,water-based optically transparent antenna and array antenna decoupling technologies are studied in this paper,corresponding works have been conducted.Works of this paper are given as follows:(1)A wideband and compact water antenna with optically transparent characteristic is proposed.This antenna mainly consists of a fan-shaped cylindrical radiator,a top disk load,a cylindrical base and a distilled water ground.Based on two resonant modes,this antenna can achieve wideband characteristic.Meanwhile,when combined with fan-shaped radiator and top disk loading,the overall dimensions can be greatly reduced without compromising impedance matching.The ground made of distilled water is used for full transparency.The proposed antenna covers frequency range from 1.16 to 2.79 GHz for₁₁<-10 d B.The proposed antenna shows relatively wide bandwidth(82.5%)in the field of transparent antennas,without sacrificing size and radiation performance.(2)The phase-regulation-based decoupling reflector is proposed for reducing the mutual coupling between antenna elements in MIMO array antenna.The phase-regulation-based decoupling reflector consists of a number of electrically small metallic reflectors loaded by stubs and is printed on a thin substrate.Reflected phase can be changed not only by changing the placement height of phase-regulation-based decoupling reflector,it can also be regulated by designing stubs.Therefore,compared with array antennas using Array-Antenna Decoupling Surface,an array antenna using phase-regulation-based decoupling reflector will have a lower profile,and phase-regulation-based decoupling reflector is more suitable for massive multiple-input multiple-out array antenna.Principles of phase-regulation-based decoupling reflector are illustrated by theory and simulation analysis,and the effectiveness of phase-regulation-based decoupling reflector is proved.Two examples with single-polarized and dual-polarized configuration are fabricated and measured to prove the versatility of phase-regulation-based decoupling reflector.Maximum isolation enhancement and decoupling fractional bandwidth of single-(dual-)polarized examples respectively reaches 29(33)d B and 17(14)%.(3)Considering the difficulty of realizing wideband decoupling,the concept of wideband high isolation reconfigurable array antenna is proposed.Based on the feature that the phase of reflected wave can be adjusted by varying stubs of phase-regulation-based decoupling reflector,a reconfigurable structure is proposed by using pump to pump into or out ethyl acetate from the microfluidic,and regulation of reflected phase can be realized.The concept of wideband high isolation reconfigurable array antenna is realized by combining a 1×2 stacked patches array antenna,corresponding phase-regulation-based decoupling reflector and the reconfigurable structure.Simulated and measured results show that the operational frequency band ranges from 1.83?2.17GHz.The isolation of wideband high isolation reconfigurable array antenna below than-35d B can be continuously and stably scanned within 1.9?2.17GHz,the isolation below than-25d B can be continuously and stably scanned within the whole operational frequency band.Therefore,wideband high isolation reconfigurable array antenna can realize wideband decoupling in disguised form.