Design Of The Wearable Antennas Based On Periodic Structures

As a kind of antenna applied in wireless body area networks(WBANs),wearable antennas need to meet the design requirements such as miniaturization,stability,comfortability and security,which puts forward higher requirements for the antenna design.Meanwhile,periodic structures in microwave fields can be used to improve some parameters of antenna because of their unique electromagnetic properties.electromagnetic band-gap(EBG)and metasurface are two kinds of planar periodic structures,whose applications in the wearable antenna design are mainly studied in this paper.There are five wearable antennas are designed in this paper,which can be applied in the wireless local area network(WLAN)communication,and their operating bands can cover 2.4-2.4835 GHz or 5.15-5.825 GHz.The main contents of this paper are listed as follow:1.Design of wearable antennas based on EBG structuresAccording to the feature of in-phase reflection,there are two wearable antennas loaded with EBG arrays designed in this paper,in which the proposed monopole antenna with a novel uniplanar compact EBG(UC-EBG)can be used for 2.4 GHz WBAN applications,and the wearable microstrip antenna based on a novel dual-band EBG array can operate in the 2.4GHz and 5-GHz WLAN bands.The equivalent circuit model is utilized to analyze the relationship between resonant frequencies of the EBG structures and equivalent capacitance and inductance can be obtained.Based on the experimental analysis,it can be concluded that the EBG structures can reduce the back lobe of antenna,increase the antenna gain,and reduce the SAR value significantly.Therefore,loading EBG structures in wearable antenna is an effective way to improve the antenna performance.2.Design of wearable antennas based on metasurface structuresBased on the theory of characteristic mode analysis(CMA),the radiation characteristics of metasurface antenna can be analyzed from physical level,and thistheory can be utilized to analyze and design uniform and even nonuniform metasurface.The first antenna covered with metasurface layer was simplified based on the CMA,which is realized by removing the three inefficiently coupled unit cells from the 3×3 metasurface array.The radiation performance is rarely affected after simplification.The second one is an omnidirectional slot-coupling antenna with nonuniform metasurface layer,and its omnidirectionality is obtained by exciting the corresponding characteristic mode of metasurface.The third antenna is a cylindrical nonuniform metasurface wideband antenna.The two dominant modes are excited in the design band based on characteristic currents distribution of metasurface,which can expand bandwidth of the proposed antenna.Metasurface covered layer can utilized to achieve different functions in wearable antenna design,and the nonuniform metasurface designed based on the CMA have advantages over uniform metasurface in some cases.