Design Of Wearable Antennas Based On Characteristic Mode Theory

With the rapid development of WIFI technology and Io T technology,and the widespread use of wearable devices,wearable antennas for Wireless Body Area Network(WBAN)have gradually become a research hotspot,especially the wearable antennas working in 5 GHz band(5.15-5.825 GHz),because they can achieve 1 GHz bandwidth and high data transmission rate of 10 Gb/s,thus gaining great attention.Microstrip patch antennas have the advantages of miniaturization,low profile,and light weight,and are often used in the design of wearable antennas,however,the frequency bandwidth of classical microstrip patch antennas is usually narrow and must be bandwidth extended to function in the 5 GHz band,and the characteristic mode theory studied in this thesis has been widely used to guide the design of broadband antennas due to its clear theoretical explanation.Therefore,in this thesis,a series of studies on the design process of wearable microstrip patch antenna are carried out under the guidance of characteristic mode theory,and the targeted antenna design and the gradual change of antenna structure are realized based on characteristic mode theory,which are mainly as follows.1.Linearly polarized dual-band wearable antenna based on characteristic mode theoryBased on the results of the characteristic mode analysis of the double-layer circular patch structure,a single-band antenna operating in the 5 GHz band is proposed by gradually modifying its structure to achieve the directional shift of the characteristic mode.Considering that the wearable antenna sometimes requires to work in multiple frequency bands,in order to achieve dual-band resonance,the upper layer of the single frequency antenna is changed to a periodically arranged 3×3metasurface structure,and the resonance range of 5 GHz band is widened by more excitable modes brought by the metasurface structure,and then based on the prediction of the resonance point by characteristic mode,a linearly polarized dual-band wearable antenna was designed by redistributing the slit of the antenna middle patch to add resonance at the commonly used frequency point of 2.45 GHz on the antenna without affecting the high frequency resonance,and the measured relative impedance bandwidth of the antenna is 1.2%(2.43-2.46 GHz)and 39.7%(4.68-6.60GHz),respectively.2.Single-layer metasurface wearable antennas based on characteristic mode theoryThe metasurface structure in the designed linearly polarized dual-band wearable antenna is studied individually,and the selected modes are excited by modifying its structure,and two single-layer metasurface antennas are successively proposed by combining different modes.Firstly,the short-circuit probe and slit loading are used to achieve the directional shift of the three linearly polarization modes of the antenna,so that the linearly polarization modes of the antenna are concentrated around 5.5 GHz and successfully excited,with a relative impedance bandwidth of 21.8%(4.93-6.13GHz),which completely covers the 5 GHz band.After that,two orthogonal modes of the basic metasurface structure are selected for the construction of the circularly polarized antenna,and the L-shaped slit loading is used to adjust the two orthogonal modes simultaneously,so that the two modes intersect at 5.5 GHz and the characteristic angle difference is maintained at about 90 degrees,and finally the relative impedance bandwidth of 16.7%(5.05-5.97 GHz)and 9.6%(5.17-5.69 GHz)of 3 d B axial ratio bandwidth.