| In this thesis,the beam broadening and miniaturization technology of ultra-wideband(UWB)circularly polarized antenna are studied.The main research work includes the following three aspects:1.The design principle of UWB spiral antenna is studied.Firstly,the input impedance of the self-complementary antenna is deduced based on the Babinet principle,and then the design principles of the spiral antenna and the conical spiral antenna are summarized based on the similarity principle.Secondly,according to the requirements of the antenna feed,the design principle of the UWB matching balun is expounded.Finally,an ultra-wideband exponentially gradient balun with a working bandwidth of(15:1)is designed according to the principle,which provides a basis for the subsequent design of the feed of related antennas.2.The beam broadening technology of the ultra-wideband circularly polarized antenna is studied.A wide beam spiral antenna with a working bandwidth of(2:1)and a hemispherical beam conical spiral antenna with a working bandwidth of(2.25:1)are designed respectively.First of all,according to the requirements of the design target,the appropriate spiral gradient rate is selected,which broadens the beam coverage of the antenna.Secondly,by loading a special-shaped reflective cavity,the radiation performance of the antenna at the high frequency in the working band is improved,and the circular polarization gain of the spiral antenna is greater than-1.1d Bic in the 120° beam coverage area,and the circular polarization gain of the conical spiral antenna is greater than-6.5d Bic in the hemispherical beam coverage area is realized.Finally,the designed ultra-wideband hemispherical beam conical spiral antenna is processed and tested,and the beam broadening effect of changing the spiral gradient rate and loading the special-shaped reflective cavity technology on the ultrawideband spiral antenna is verified.3.The miniaturization technology of the ultra-wideband circularly polarized antenna is studied.A miniaturized composite spiral antenna(CPSA)with a working bandwidth of(9:1)and a miniaturized variant conical spiral antenna with a working bandwidth of(15:1)are designed respectively.Firstly,in order to ensure the full-band radiation performance of the antenna when the radial size is 81% of the theoretical value,a CPSA that combines two spiral gradient rates is designed.Then,by loading a helix at the end of the spiral,the truncation effect at the end of the spiral is further weakened,and the gain of the antenna at the low frequency in the working band is improved.On this basis,by loading an ultra-wideband special-shaped reflective cavity,the antenna has stable unidirectional radiation characteristics with a working bandwidth of(9:1),and the circular polarization gain is greater than-2.6d Bic within the range of 80° beam coverage.After that,through the combination of meandering and lumped loading technology,the miniaturization of the conical spiral antenna is further realized,and its radial size is reduced to 56% of the theoretical value.In order to solve the problem of the concave radiation pattern of the antenna at the high frequency in the working band,a variant conical composite spiral antenna is proposed based on the miniaturized conical spiral antenna designed above.After the optimized design,the circular polarization gain of the antenna in the L-band is greater than-1.5d Bic in the θ= 0° direction,within the 90° beam coverage,the circular polarization gain is greater than-4.4d Bic,and in the S Ku band,the circular polarization gain of the θ= 0°direction is greater than 5.2d Bic,within the 90° beam coverage,the circular polarization gain is greater than 1.7d Bic and in the full band,the axial ratio of the θ= 0° direction is less than 6.7d B.Finally,the miniaturized conical spiral antenna with a working bandwidth of(15:1)is processed and tested,which verifies the effectiveness of the fusion design of miniaturized technologies such as loading helix,meandering and variable cone angle. |
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