Research Of Metasurfaces In Wearable Antennas And Reflector Antennas

The metasurfaces?MS?is derived from metamaterials and it is the two-dimensional?2D?equivalent structure of metamaterials.Compared with the 3D metamaterials,MS has a smaller physical size and a smaller loss,and these advantages make it widely used in antennas.This thesis mainly applies MS to wearable antennas and reflector antennas.The research contents and main results are as follows:1.Three analysis models or theories of MSIn this thesis,three analysis models or theories of MS are introduced for different application forms of MS in antenna design:1)Model of equivalent electromagnetic parameters based on effective medium theory,which is derived from the average of fields in periodic elements.The model uses the Nicolson-Ross-Weir?NRW?method to obtain the equivalent electromagnetic properties of the MS;2)Theory of characteristic mode analysis?CMA?based on the method of moment?MoM?,which proposes that all orthogonal characteristic modes are intrinsic property of conductors.The solution of this theory is convergent and complete,which can accurately solve electromagnetic problems;3)Model of reflection phase shift based on the optical theory,which can change the propagation of electromagnetic wave by evaluating the phase mutation or polarization generated by MS.These models and theories not only enrich the application of MS in wearable antennas and reflector antennas but also have been verified in various proposed antennas.2.Three proposed wearable antennasThis thesis proposes three wearable antennas that work in the 5-GHz wireless local area network?WLAN?band.The proposed antennas are evaluated by the wearable performance test including human body measurement,bending simulation and specific absorption rate?SAR?simulation.Among them,the proposed broadband inverted-F wearable antenna realizes the expansion of working bandwidth by using the single-patch multi-mode method.In this antenna,the variation of the electric field distribution is used to qualitatively explain the adjustment of the resonant frequencies of TM_0,1/2 and TM_0,3/2 modes by loading shorting pins and the slot.This antenna has a-10 dB bandwidth of 990 MHz and a fractional bandwidth of 18.0%,which can completely cover the entire 5-GHz WLAN band.In the proposed broadband wearable MS antenna,the loading of the MS not only realizes the miniaturization but also improves the radiation performance.By comparing the return loss and input impedance with or without loading the MS,the size of the proposed antenna can be reduced.The distribution of surface currents and the radiation patterns of the feed antenna,the MS antenna,as well as the feed antenna loading with the the equivalent dielectric explain the mechanism of the improvement in antenna radiation performance.This antenna has a peak gain of 6.70 dBi and a-10dB bandwidth of 940 MHz?which covers the entire 5-GHz WLAN band?.It has significant performance and size advantages over other wearable antennas operated in 5-GHz WLAN band.The proposed frequency reconfigurable wearable MS antenna utilizes a reconfigurable MS to greatly simplify the mechanical motion of the mechanically reconfigurable antenna and it also achieves the frequency tuning from 5.11 GHz to 5.86 GHz?750 MHz?.The model of equivalent electromagnetic parameters provides a guiding reference for the optimization of the reconfigurable MS.The theory of CMA systematically analyzes the mechanism of the reconfigurable resonant frequency and the formation of the radiation patterns.3.Two proposed quasi-Cassegrain antennasThis thesis proposes two quasi-Cassegrain antennas that operate in different frequency bands.Based on the theory of optics and the traditional Cassegrain antenna,this thesis proposes a quasi-Cassegrain antenna.The quasi-Cassegrain antenna can indeed reduce the profile while maintaining the excellent radiation performance of the reflector antenna.The proposed 8-GHz broadband quasi-Cassegrain antenna has a profile of 0.71?₀,a peak gain of 15.9 dBi,and a-10 dB bandwidth from7.45 GHz to 8.52 GHz?a fractional bandwidth of 13.4%?.The proposed 5-GHz WLAN quasi-Cassegrain antenna eliminates the shielded vias to further simplify the antenna structure.This antenna has a profile of only 0.244?₀ and a peak gain of 13.7 dBi with the operating band covering one band of the 5-GHz WLAN.