Research On Functionality Extension Of Miniaturized Antennas

With the rapid development of modern wireless communication system,the miniaturization of wireless platforms is becoming the inevitable trend of the development of wireless communication system,which makes the antenna miniaturization become a mandatory requirement.Meanwhile,the wireless communication system also requires the antenna to hold multi-functional properties,especially in the fields of radio frequency identification system(RFID),aeronautical communication and marine communication.Consequently,the functionality extension of the antenna has attracted extensive attention.Therefore,the realization of the functionality extension of the antenna under the condition of antenna miniaturization that is a very promising research subject.Therefore,several researches referring to the miniaturized antennas have been accomplished in this thesis.In details,the antennas are,respectively,integrated with filtering and pattern reconfigurability.This thesis mainly contains the following two parts:(1)A planar electrically small antenna with broad bandwidth and high out-of-band rejection level is proposed.The antenna mainly consists of a driven patch and a ground plane.In our method,the resort of etching two slots in the ground plane to form two square ring patches can generate a new resonant mode and two radiation zeros,and the employment of loading a T-shaped branch can not only expand the antenna bandwidth but also improve the out-of-band suppression level.Then,the antenna was fabricated and measured.The measured results show that the center frequency of the antenna is2.95 GHz,the fractional impedance bandwidth is 23.05%,and the realized gain values3.29 d Bi in the operational band.Finally,the planar electrically small antenna can realize the extension of filtering functionality while taking into wide bandwidth even when the electrical size parameter ka is only 0.98 and the profile height is only 0.014?₀(?₀ is the free-space wavelength corresponding to the center operating frequency in the working frequency band),which is suitable for noise signal filtering outside the wide passband of wireless communication system.(2)A miniaturized planar quadrifilar helix antenna with broadside and monopole-like pattern reconfigurability is presented.The proposed pattern reconfigurable antenna is mainly composed of a simple reconfigurable feed network,two sets of reconfigurable folded spiral arms with central symmetric structure,and three directed rings.By switching the ON/OFF status of PIN diodes on the feed network and the folded spiral arms,the radiation modes of the quadrifilar helix antenna could be altered between broadside and monopole-like patterns,and the circular polarization of the broadside pattern state can also be realized at the same time.In two pattern-reconfigurable states,the antenna peak realized gains are 3.14 d Bi and 0.9 d Bi,respectively,and the overlapping fractional impedance bandwidth(FBW)is 6.3%.Finally,the miniaturized quadrifilar helix antenna can realize the extension of pattern-reconfigurable functionality even when the transverse size of the antenna is only0.14?₀²,which is suitable for RFID reader with low power consumption.