Study Of Flexible,electrically Small,quasi-isotropic Antenna

-Compared with the ordinary omnidirectional antennas,which can achieve a 360° signal coverage from all directions for communication in a certain plane,quasi-isotropic antennas can perfectly cover the entire three-dimensional space and realize the reception and transmission of signals in all directions.Due to the rapid development of modern communication technologies and the introduction of various concepts of body area networks and even the Internet of Things(Io T),devices movements have become more and more important.Therefore,how to design and develop antennas suitable for various application environments has become an increasingly important issue.As we all know,human health and daily life are the two aspects that people are most concerned about.This requires that the antenna not only have lightweight characteristics,but also adapt to the surface of the human body and objects as much as possible to be suitable for various physical conditions and to monitor the health conditions.Therefore,the miniaturized flexible antenna has become the best choice.The flexible quasi-isotropic antenna can not only achieve full space coverage,but also realize moving signal reception after the signal source position changes.Both space-constrained object surfaces and human body surfaces have broad application prospects.This thesis presents a relatively simple,low-cost,flexible,uniplanar,and electrically small quasi-isotropic antenna,and conducts related experimental research.Mainly completed the following tasks:(1)By comparing the materials of various flexible antennas,a PDMS(Polydimethylsiloxane)substrate is suitable for manufacturing quasi-isotropic antennas.In this process of PDMS manufacturing,the hardness of the PDMS film can meet the experimental requirements by controlling the curing temperature,de-voiding time,annealing temperature and time.Comparing various conductive materials and metals,silver paste was selected as the conductive medium and radiation material from the prospective of material manufacturing and availability.Relevant researches on the spraying and coating methods of nano-silver wires contributes to determine the coating method to generate the radiating structure.The silver paste is attached to the PDMS substrate to form a quasi-isotropic antenna structure.Then the conducting medium and substrate made the antenna flexible.(2)Design and simulate the electrically small quasi-isotropic antenna.This antenna consists of a pair of driven strips and a split ring resonator(SRR),and all antenna structures are printed on the same side of the substrate.The split ring has two inwardly folded strips on the side of the opening gap.The split-ring resonator can generate a pair of equivalent electric dipole and magnetic dipole,so it can achieve omnidirectional radiation patterns along with the x-axis and y-axis,respectively,and it is worth noting that the amplitudes of the realized gains are almost equal.By superimposing the two orthogonal radiation patterns of equivalent electric dipole and magnetic dipole with each other,the antenna can finally form a quasi-isotropic radiation pattern.In the simulation process,by changing various parameters of the antenna,the antenna can be operated at different frequencies to meet the working requirements of different environments;through change related material parameters,the radiation efficiency of the antenna can be improved.(3)Fabricate and test the antenna.In order to improve the testing accuracy,a 1/4 ?sleeve balun was added to the surface of the coaxial cable of the antenna.The test results are in good agreement with the simulation results.The maximum gain difference on the entire radiating sphere is about 3 d B,which can achieve an electrically small size(0.154 × 0.154 × 0.0004 ?3,ka = 0.68)and the overall efficiency is 77%.In addition,several related flexibility tests have been conducted.The antenna is attached conform to the surface of the foam cylinder.Through varying the radius of the cylinder,different bending conditions of the antenna could be achieved,and then test the various performances of the antenna.The characteristics remain the same overall,demonstrating the stability of the antenna's performance in different bending conditions.The above-mentioned antenna simulation and optimization process are completed by Ansoft high-frequency electromagnetic simulation software HFSS(High Frequency Structure Simulator).The reflection coefficient is measured by Keysight Vector Network Analyzer and the far-field parameters of the antenna are tested by SATIMO chamber.