Research And Application Of Electronically Steerable Parasitic Array Radiators

With the popularity of Internet of Things(Io T),Smart City and 5G technology,Electronically Steerable Parasitic Array Radiators(ESPAR)are gaining more and more attention in the establishment of Io T gateway and wireless sensor network due to their low cost,high stability and adjustable radiation direction of pattern,etc.Compared to phased array antenna,ESPAR antenna usually has single feeding unit and multiple parasitic units which are closely arranged.Based on the near-field coupling principle,reactive load is used to replace the phase shifter,which can reduce the cost and power consumption of the system.For ESPAR antenna,extending the operating bandwidth,reducing the effect of side lobe and back lobe and beamforming are three important research areas.In this thesis,on the basis of ESPAR antenna with reconfigurable pattern,an in-depth study on working bandwidth extension,gain enhancement and the influence of feed circuit are carried out as follows:Firstly,the expanion of working bandwidth for ESPAR antenna is researched.In order to solve the problem of narrow working bandwidth of ESPAR antenna,a C-band wind-band ESPAR antenna is studied and designed.By introducing square ring patch and metal microstrip line with reactive load,the antenna has several radiation structures working at different resonant frequencies,so the working bandwidth of the antenna increases to 4.85GHz-6.25 GHz,with a central frequency point of 5.75 GHz,and a relative bandwidth of 24.35%.The average gain of antenna within the working bandwidth is 4.8d Bi,the radiation efficiency is 90%,and the pattern can be reconstructed.Secondly,the improvement of gain for ESPAR antenna is researched.In order to solve the problem that the parasitic elements of ESPAR antenna have a great influence on the side lobe and back lobe of radiation pattern,a low-profile and high-gain circular patch ESPAR antenna is studied and designed.The overall height of the antenna is6.2mm,and the working bandwidth of the antenna is 2.28GHz-2.53 GHz,covering the WLAN band.Meanwhile,the average gain of ESPAR antenna is 7.7d Bi and the maximum gain is 8.9d Bi.By adding reactive load to the parasitic unit,the antenna has four main lobe radiation modes,0°,90°,180° and 270°.Thirdly,the effect of feed circuit for ESPAR is investigated.According to the principle of adding reactive load at the end of the parasitic units of ESPAR antenna,a circularly polarized dielectric ESPAR antenna is studied and designed by making the phase of a single parasitic unit different from the other parasitic units to adjust the radiation direction of the main lobe of the pattern.The antenna works at2.38GHz-2.52 GHz,with a relative bandwidth of 5.72%,and a center frequency of2.45 GHz.The average gain in the working bandwidth is 6.5d Bi,the average radiation efficiency is 92%,and the working bandwidth covers WLAN band.By adding reactive load to the parasitic unit,it has four working modes with an average gain of 7.48 d Bi.By adding an orthogonal metal microstrip line,the antenna has a 3d B axial ratio(AR)bandwidth of 6.8% at 170 MHz in the operating band.