| With the continuous improvement of wireless communication quality,high-performance antenna technology with higher gain,lower sidelobe and purer circular polarization purity has attracted a lot of attention.The reasons include the following points: Firstly,antennas with higher gain can emit and accept signals farther away and achieve strong directional radiation;Secondly,the antenna with lower sidelobe level can effectively reduce the interference of other stray signals and improve the anti clutter ability of the communication system;Finally,the improvement of circular polarization purity means that the cross polarization discrimination rate increases,that is,the cross polarization component of the antenna decreases,which further optimizes the performance of the circular polarization axis ratio.Microstrip antenna also has many advantages,such as small volume,easy to change shape,circular polarization,low cost,integration and so on.To sum up,the research on high gain and low sidelobe circularly polarized microstrip array antenna has become the general trend of antenna development and one of the research hotspots.In this thesis,two kinds of high gain and low sidelobe circularly polarized microstrip antenna arrays are proposed by studying the research status of the microstrip circularly polarized array antennas at home and abroad.The array form,circular polarization design and feed network design are discussed.The main research work and contributions of this thesis are as follows:(1)A novel circularly polarized microstrip antenna array with high gain and low sidelobe is proposed.The antenna element adopts corner truncated circularly polarized stacked microstrip structure.The symmetry of the antenna array directivity diagram and the optimization of the circularly polarized radiation performance are realized by the octagonal boundary and sequential rotation overlapping array techniques.The feed network adopts Wilkinson power divider and third-order flat impedance converter to achieve unequal power division and broadband impedance matching.The design of the feed network is simplified by adjusting feed direction to seek symmetrical structure.The antenna array is fabricated and measured.The test results show that |S11| is less than –10 dB within the frequency band of3.2~4.6 GHz,and the relative impedance bandwidth is 33%.In the frequency range of3.8~4.5 GHz,the zenith axial ratio is less than 3 dB and the relative circular polarization bandwidth is 17%.In the frequency range of 4~4.4 GHz,the antenna gain is above 15 dBi,and the maximum gain is 17 dBi,the first lobe level of the antenna at the center frequency of4.2 GHz is up to –15.7 dB.(2)A novel high gain low sidelobe circularly polarized microstrip antenna array for 5.8GHz is designed based on two kinds of element structures.The two kinds of antennas use the truncated corner and the bias feed to separate the modes to achieve circular polarization radiation and the embedded feed to adjust the impedance of the antenna unit,which facilitates the design of the unequal power ratio feed network.The antenna array is composed of an inner 4-element rectangular array and an outer 8-element toroidal array.By optimizing the cell spacing and power ratio,the gain is increased and the side lobes are reduced to form a pen beam directivity pattern.To further improve the circular polarized radiation performance,the peripheral 8-element ring array uses 45 degree sequential rotation technology to widen the axis ratio bandwidth.The antenna array is fabricated and measured.The test results show that|S11| is less than –10 dB within the frequency band of 5.67–6.17 GHz,and the impedance bandwidth is 500 MHz.In the frequency range of 5.67–5.975 GHz,the zenith axial ratio is less than 3 dB and the relative circular polarization bandwidth is 5.2%.In the frequency range of 5.61–5.92 GHz,the antenna gain is above 16 dBi,and the maximum gain is 18 dBi,the first lobe level of the antenna at the center frequency of 5.8 GHz is up to –16.3 dB. |
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