Research On Widebeam Antennas And Multi-Polarized Antennas

With the rapid development of information science and technology,wireless systems are being widely applied in the real life,which puts forward higher requirements on the front end of wireless system-antennas,such as the desire for antennas with wide beam characteristics to expand the signal coverage,broadband or multi-band characteristics to increase the information capacity,multi-polarization or circular polarization to enhance the ability to resist multipath interference.To fulfill the requirements of wide angle scanning for phased array antenna and the mitigation of the multipath fading,a series of studies have been carried out on the applications of wide beam antennas,their arrays and multi-polarized antennas,the corresponding solutions are presented in this paper.The main contents and work of the thesis are concluded as follows:1.The research status and developments of wide beam antennas and their arrays,multi-polarised antennas and their bandwidth extension technologies are analyzed and reviewed.Although great progress has been made in this field,lots of problems still need to be solved.2.A planar wide beam antenna based on dual-mode resonance is proposed.An electric dipole transfer energy into two resonators and dual resonant points are generated.Because one edge of each resonator opens and produces an equivalent magnetic current on the aperture,the antenna has nearly omnidirectional radiation characteristic in the E-plane.The test results indicate that the half power beamwidth(HPBW)of E-plane is greatly expanded compared with the traditional microstrip antenna,and the operation of two modes also widen the bandwidth.Eight-element phased array antenna with half-wavelength inter-element spacing is designed using the aforementioned element,and the wide-angle scanning characteristics is studied.The element of the array maintains a good impedance matching and wide beam characteristics,and the mutual coupling is weak.The test results indicate that the main beam direction of the array can scan from-60 degrees to +60 degrees with a gain fluctuation less than 3dB,and the scanning 3dB beamwidth can cover a range from-76 degrees to +78 degrees.Finally,the hybrid IWO/PSO algorithm is used to optimize the aperture current distribution,the sidelobe level is reduced obviously.3.Based on the SIW cavity structure,a planar wide beam antenna operating at 5.7 GHz is proposed.This antenna is based on the working principle of magnetic dipole to broaden the beamwidth.The test results show that the E-plane HPBW is 145 degrees and the H-plane HPBW is 110 degrees,which is a good candicate for the wide-angle scanning array applications.A circularly polarized antenna with axial-ratio wide-beam feature is also proposed,which consists of four sequentially rotated inverted-F antennas.The scanning feature is also studied.4.A novel horn antenna with circular polarization feature is proposed.A piece of metal sheet is used to split the TE11 mode of circular waveguide,generating orthogonal electric fields with equal amplitude and 90 degrees phase difference to realize circular polarization.Then,the method of sequentially rotation is used to improve the performance of circular polarization,and the wide angle scanning characteristics under the circumstance of equal amplitude and amplitude tapering is investigated.5.A series of beneficial explorations have been made on the bandwidth expansion of dual-polarized and circularly polarized antennas.The dual-polarized dielectric resonator antenna utilizes the TE111 mode and TE113 mode in the same resonator to realize dual band.A balanced feed structure is used to cancel the cross polarization component,and the isolation is increased to-60 dB.A circular polarization antenna working at 1.5-2.18 GHz is designed by using the broadband characteristic of the bowtie sturcture,and the symmetry of the radiation pattern is maintained.Based on the mechanism of different current paths generated on the annular slot with fractal structure,a compact dual-band circularly polarized microstrip antenna is designed.The effect of fractal geometry and feeding structure on the performance of antenna is analyzed in detail.6.Conclusion and prospect.The main work of this thesis has been reviewed and summarized.The shortcomings are proposed and the work in the future is introduced.