Theory And Methods Of Bandwidth Enhancement Based On Band Merging For Textile SIW Antennas

The textile substrate-integrated waveguide(SIW)antenna is of great potential in wearable applications because of its advantageous planar structure,high flexibility and easy integration.However,the textile SIW antennas are narrow-band antennas,and the present mainstream bandwidth-enhancing methods for textile SIW antennas have defects including small bandwidth increase,large cavity size and low radiation efficiency.As a result,it is difficult for the textile SIW antennas to deal with the frequency shifting caused by the human body or deformations or to be reused in multiple frequency bands.Therefore,the research of the theory and method of bandwidth enhancement for the textile SIW antenna to expand the its bandwidth,enhance its performance,and promote its application in medical monitoring,sports,defense,security,personal communication and other fields is of high research values and application prospects.In view of the remarkable effects of the bandwidth enhancement method based on band merging for microstrip patch antennas(MPAs)and planar inverted F antennas(PIFAs)proposed by relevant literatures,the idea of band merging for MPAs/PIFAs is introduced in this dissertation to carry out researches on the theory and method of bandwidth enhancement for textile SIW antennas,to design high-performance textile SIW antennas with large bandwidth increases,small sizes and high radiation efficiencies to solve the problem of the insufficient bandwidths of textile SIW antennas.The main works of this dissertation are as follows:(1)The cavity model and operation mechanism of SIW antennas are analyzed.Firstly,the cavity models of a rectangular resonant cavity and a half-mode substrateintegrated cavity(HMSIC)antenna are established,the theoretical expressions of the resonant frequencies and internal electric fields of the fundamental and higher-order modes are derived,and the normalized simulations for the internal electric field distributions of the fundamental and higher-order modes are carried out.Secondly,the operation mechanism of a coupled-mode substrate-integrated cavity(CMSIC)antenna is theoretically analyzed,the principle of the dual-fundamental-mode characteristic is revealed,the theoretical expressions of the H-plane gain in two coupled modes are derived,and the normalized simulations for the H-plane gain patterns in two coupled modes are carried out.(2)A method of band merging and bandwidth enhancement based on shorting vias for the textile HMSIC antenna is proposed.Firstly,based on the modified expression of the resonant frequency of the fundamental mode,a basic textile HMSIC antenna is designed with its higher-order mode frequency tuned around 5.5 GHz through parameter sweeping with Hfss.By adding short vias along the zero-E path of the higherorder mode of the antenna,the band of the fundamental mode is shifted to the right to be merged with the band of the higher-order mode to achieve bandwidth enhancement.Based on that,a bandwidth enhanced textile HMSIC antenna loaded with metallic rivets as short vias is designed.In addition,the improving methods of shorting vias and feed structure are proposed,and a bandwidth enhanced textile HMSIC antenna loaded with embroidered shorting vias and shielded textile stripline feeding structure is designed.Simulation and measurement results show that the two antennas are of measured-10 d B fractional bandwidths of 19.7% and 14.7%,respectively,which can cover the 5 GHz WLAN band.Compared to the basic textile HMSIC antenna,their bandwidths increase by 198% and 123%,respectively.Besides,their simulated radiation efficiencies are above 98% and 95% respectively.However,their cavity sizes are relatively large due to the increase of the frequency of the fundamental mode.(3)A method of band merging and bandwidth enhancement based on V-slot for the textile HMSIC antenna is proposed.Firstly,based on the modified expression of the resonant frequency of the fundamental mode,a basic textile HMSIC antenna is designed with its fundamental mode frequency tuned around 5.5 GHz through parameter sweeping with Hfss.By adding a V-slot on the conductive top layer of the antenna,the band of the higher-order mode is shifted to the left to be merged with the band of the fundamental mode to achieve bandwidth enhancement.Based on that,a bandwidth enhanced textile HMSIC antenna loaded with V-slot is designed.Simulation and measurement results show that the antenna are of a measured-10 d B fractional bandwidths of 15.7% which can cover the 5 GHz WLAN band.Compared to the basic textile HMSIC antenna,its bandwidth increases by 138%.And its simulated radiation efficiency is above 94%.Besides,compared to the antenna proposed in(2),its cavity size decreases by 77%.(4)A bandwidth enhancing method based on triple-band merging for the textile CMSIC antenna is proposed.Firstly,based on the modified expression of the resonant frequency of the fundamental mode of the HMSIC antenna,a basic textile CMSIC antenna is designed with its fundamental mode frequencies tuned around 2.45 GHz through parameter sweeping with Hfss,and its dual-fundamental-mode characteristic is simulated and analyzed.By adding a rectangular slot on the conductive top layer,an extra band is introduced to be merged with the bands of the even and odd modes to achieve bandwidth enhancement.Based on that,a bandwidth enhanced textile CMSIC antenna based on triple-band merging is designed.A measured-10 d B fractional bandwidth of 14.9% which can cover the MBAN,2.45 GHz ISM and LTE-7 bands is obtained.Compared to the basic textile HMSIC antenna,its bandwidth increases by381%.And its simulated radiation efficiency is above 86%.In addition,based on the basic CMSIC antenna,the bands of the even and odd modes are simultaneously shifted by adding metallic snap buttons at both its radiation apertures to achieve the reconfiguration of the radiation pattern at a fixed frequency.A fixed-frequency patternreconfigurable textile CMSIC antenna is designed and fabricated.Simulation and measurement results indicate that the antenna show different radiation patterns for the on-body and off-body WBAN communications at fixed 2.45 GHz.The researches in this dissertation enrich the design theory for textile SIW antennas,improve the performance of textile SIW antennas,and contribute to the wider application of textile SIW antennas in the wearable environments.There are 114 images,7 tables and 121 references in this dissertation.