| Due to the technology evolution,the wireless communication systems are rapidly developing and upgrading towards large capacity,high-speed,compact size,stable in more complex working environment.As an important part of the wireless communication system,antenna designs with strict requirements are desired.Meanwhile,the implantable electronic devices are widely used in health examinations and medical treatments,require antennas with good biocompatibility and biodegradability.The application of metamaterials and biodegradable materials facilitates the development of antenna.Antenna designs based on the metamaterials meet the requirements of morden wireless communication systems.The biodegradable materials applied in antennas design meet the requirements for implantable devices,and also addresses the e-waste problem.This dissertation is mainly concerned with the antenna designs based on metamaterials and biodegradable materials,which effectively solve the problems exist in the modern wireless system.The major contributions of the author are listed as the following aspects:1.The research background and significance of the antenna based on metamaterials and biodegradable materials are introduced firstly.The classifications and effects of applying the metamaterials in antenna designs are desired and analyzed.The development history of the biodegradable electronics devices are presented.2.Based on metamaterials,four designs of multiband/broadband linearly polarized antennas are proposed.Monopole antenna with electric-LC(ELC)resonator,which has a low resonant frequency,are investigated to design a tri-band antenna.Further research on this antenna shows that the metasurface structure can improve the impedance match significantly and a wideband antenna is designed with metasurface loading.Meanwhile,based on the symmetry of the ELC structure,a half-cutting compact triband antenna is designed.A dual band microstrip patch antenna with composite right/left-handed loading are studied and analysed with transmission line theory,and the radiation pattern diversity in two separated working bands can be observed.All these designs features small size and tunable resonant frequencies,and can be applied in wireless communication system.3.Based on metamaterials,two circularly polarized(CP)antennas are proposed.The antenna consists of a ring slot antenna with L-shape microstrip feedline and metasurface is proposed first.With rectangle patches metasurface placed atop ring slot antenna,the antenna shows two right hand circularly polarized(RHCP)bands by excited with L-shaped microstirp feedline.The senses of CP in two bands are the same due to the feeding structure.Then,utilizing the asymmetry folded slot with modified metasurface,a dual band CP antenna is proposed.The two CP bands can be tuned separately,and the senses of CP in two bands can be controlled by adjusting the shape of metasurface and slot.A prototype with RHCP in the first band and left hand circularly polarized(LHCP)in the second is fabricated and measured.The two antennas have low frequency ratio,low profile,high gains.They can work at 2.5GHz and 3.5GHz.4.Two reconfigurable metamaterial antennas are proposed.Firstly,metasurface coupled by the slot is used as the radiator of the antenna,by adding two varactors between two units in the metasurface,the resonant frequency of the antenna can be tuned from 2.36GHz to 3.22GHz with high directivity and low profile.Secondly,two coupling units are loaded beside two arms of the dipole,and the radiation pattern can be altered among three different omnidirectional radiation patterns by controlling two diodes.The metasurface is also used in the antenna design as low profile reflector,by controlling two diodes,the radiation pattern of the antenna can be changed among three directional radiation patterns with gain more than 9dBi.The designed reconfigurable antennas all feature simple bias circuits and good tunability.5.The biodegradable materials are categorized according to their physical characteristics and application.Two antennas based on polylactic acid(PLA)substrate are proposed.Firstly,a patch antenna working in free space designed with PLA substrate is fabricated and measured.The good agreement between the simulated and measured results indicates the robust of the PLA substrate.Secondly,the implantable patch antenna working in water is fabricated with PLA substrate and copper foil through improved processement,and the antenna has two resonances.The degradation experiment for the implantable antenna is designed and carried out.The antenna is immersed in the deionized water,with a temperature higher than the dissolving temperature.The temperature of water is kept stable,and gradual dissolution of the substrate and changing of resonant frequency can be observed.During the 18 days degradation experiment,the antenna shows good biodegradability,and measured S11 results show that the resonant frequencies are constantly decreasing.This research is the first time to use biodegradable polymer in antenna design,which accumulates experimenting and manufacturing experiences of biodegradable antenna design. |
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