Design Of Low Profile Printed Antennas Based On Metasurfaces

In recent years,with the rapid development of wireless technology and the improvement of user demand,the antenna performance requirements of wireless devices have gradually increased.In many cases,only low-profile antennas can be used since the limited height of the antenna carrier platform.Therefore,low-profile antenna has become a new direction of antenna design.In the study of low-profile antenna with directional radiation patterns,artificial magnetic conductor(AMC)structures have been favored by researchers due to their adjustable reflection phase.There is a fixed phase difference between the plane wave reflected by the metal plate and the incident wave,so the metal plate is usually placed at about a quarter of the wavelength below the antenna.Moreover,the AMC structure with in-phase reflection characteristic can decrease the distance between the AMC and the antenna,thus achieving the purpose of reducing the antenna profile.Under the development trend of miniaturization and low profile of wireless devices,low-profile antennas based on AMC structures have high practical value.Accordingly,several antennas with low profile characteristics are studied in this thesis.The main contents can be summarized as follows:1.A wideband low-profile slot loop antenna based on AMC is designed.First of all,an AMC unit cell with annular and cruciform slots is designed.Then,a low-profile antenna with directional radiation patterns based on this AMC surface is proposed.The Coplanar Waveguide(CPW)feed structure used in the slot loop antenna eliminates the presence of metal on the bottom surface of the dielectric substrate,which allows the slot loop antenna can be directly attached to the AMC surface.The antenna height is further reduced.Simulated and measured results show that the antenna achieves an operation band of5.02-7.28 GHz,and the profile height of the antenna is only 0.05?_L while the directional radiation is achieved(?_L is the wavelength at the lowest operating frequency).2.A wideband low-profile circularly-polarized slot antenna based on AMC is designed.The antenna is constructed by a CPW-fed slot antenna and an AMC surface with square patches.The slot antenna radiates circularly-polarized wave through two opposite-direction slots.Furthermore,an AMC surface is placed underneath the slot antenna,which enables it to obtain directional radiation characteristics.By optimizing the parameters of the antenna,the final height of the antenna is only 0.077?_L,and a wide axial ratio bandwidth can be obtained.The simulated and measured results indicate that the low-profile antenna has an operation bandwidth of 25.8%(5.75-7.45 GHz).3.A wideband low-profile circular-polarized planar monopole antenna based on AMC is designed.The antenna consists of a CPW-fed planar monopole antenna and a slotted AMC surface.The planar monopole antenna radiates circularly polarized waves through an asymmetric ground plane and a slotted rectangular ring structure.With the introduction of AMC structure,the planar monopole antenna can obtain the directional radiation characteristics at a low profile height.Simulation and test results show that the low-profile antenna can achieve an operation bandwidth of 18.2%(4.39-5.27 GHz)with a height of only 0.058?_L.