Design Of Textile Antennas Based On Different Substrates And Electromagnetic Properties In Bending Environment

Wearable antennas are important components of smart wearable devices and plays a critical role in signal transmission.Currently,the substrates of wearable antennas have been developed into textile materials,one of the characteristics of which is good conformability with human body.Different textile materials as the substrate of the textile antenna,the performance of the antenna will be different.In this thesis,four kinds of textile materials were used as the antenna substrates,and the circularly polarized microstrip antennas and the ultrawideband antennas were designed.The performance comparisons of antennas based on different textile materials were studied,the performances of the antenna under bending conditions were also studied.The specific work of the thesis is as follows:(1)Polyester felt,polyester woven fabric,polyester/spandex blended fabric and “ke ti la”polyester woven fabric were selected as the antenna substrates(Pf,Pw,Ps and Pc were used to represent the above textile materials respectively).The antenna size is determined by the dielectric constant of the fabric.The dielectric constants were obtained by reverse educing method and it was found that the dielectric constant value varied as the fabric structures and gram per square meter were changed.Then,the optimum dimensional parameters of the antennas were obtained during the process of simulation optimization,and the antennas of four textile substrates were fabricated by screen printing method.The obtained antennas owned integrated structures.SEM observation showed that the silver paste on the surface of the conductive parts of antennas were uniform and compact.(2)The electromagnetic performances of the circularly polarized microstrip textile antennas and the textile ultra-wideband antennas were tested.The results showed that: the measured resonant frequencies of the circularly polarized microstrip textile antennas based on four textile substrates had good agreement with the simulation value,and all the return losses were lower than-10 d B.The gains were 10.05 d B(Pf),5.89 d B(Pw),7.58 d B(Ps)and 7.46 d B(Pc),respectively.And the axial ratios were 3.21 d B(Pf),5.98 d B(Pw),1.69 d B(Ps)and0.52 d B(Pc),respectively.The ultra-wideband textile antennas based on four textile substrates generally covered 2-6 GHz range and the gains at the representative frequency points were higher than 3 d B.The results showed that the textile antennas with Pf and Pc substrates had better comprehensive indicators.The reasons behind the above phenomena lies in the evenly distributed fibers and smooth surface of Pf and less buckling waves in yarns of Pc,all of these have positive effects on the antennas with good electromagnetic radiation characteristics.Additionally,Pf and Pc were pure polyester owing very stable dielectric properties.(3)The electromagnetic performances of the circularly polarized antennas with three substrates(Pf,Pw,Pc)bent under different radius of curvature(R)were studied.It was found that the resonant frequencies in the banding environment had small shift than the plane state,and the return losses were lower than-10 d B;when R was set as 50 mm,the gain of the antenna with Pc substrate was higher than 6 d B and the axial ratio was lower than 3 d B.The electromagnetic performances of the ultra-wideband antennas with three substrates(Pf,Pw,Pc)bent under different radius of curvature(R)were tested.The results showed that the return losses were lower than-10 d B in the frequency band range of 2-6 GHz.When R was set as 50 mm,the minimum frequency coverage is 2.88 GHz;when R was set as 50 mm,the minimum gain of antenna with Pc substrate was 4.20 d B,which met the working requirements.In addition,it was found that when Pf and Pc were used as the substrates,the circularly polarized antennas had good antenna performance after bending,which was basically consistent with the plane state.However,when the ultra-wideband textile antennas were bent,the deformation of the fabric part was inconsistent with the metal floor part,which was easy to cause the instability of the antenna performance.While,Pw and Pc are both woven structures,and their yarns were interwoven and stable,so the corresponding ultra-wideband textile antennas had better performance.