| The research works are made on the basis of National Natural Science Foundation of China “Research on electromagnetic wave regulation method based on frequency triggering mechanism and tunable device of metamaterial”.Researches on the curved reflection array antennas based on artificial meta-surface in this dissertation.This dissertation consists of two main parts: First one presents the single-meta-mirror and dual reflecting meta-mirrors on curved platforms with different structures,including umbrella-shape and polygon prism convex meta-mirrors,as well as concave,planar,and convex dual reflecting meta-mirrors.The high gain radiation patterns are well demonstrated on series of curved platforms both numerically and experimentally.The second part presents the reflecting meta-mirrors to generate orbital angular momentum(OAM)vortex waves on curved platforms with different structures.The high efficient generations of OAM vortex waves are well demonstrated on series of curved platforms both numerically and experimentally.The author's major contributions are outlined as follows:1.Convex reflecting array antennas based on meta-surfacesTwo convex conformal reflecting array antennas based on artificial meta-surfaces are proposed on umbrella-shape and polygon prism platforms,where the artificial meta-surfaces are devised according to the generalized Snell's law and the incoming radiations from feed are well collimated through the simulations and optimizations of the unit of meta-surfaces,so that the highly directive pencil-beams and fan-beams are generated respectively.The full-wave simulations demonstrate the meta-surface based umbrella-shape and polygon prism convex reflectors obtain the maximum gains of 22.5 dBi and 15.6 dBi at the center frequency of 20 GHz,where these results are 17.22 dBi and 12.3 dBi higher than the umbrella-shape and polygon prism bare convex reflectors without meta-surfaces.Moreover,the meta-surface based umbrella-shape and polygon prism convex reflectors obtain the satisfactory reflection coefficient modulus that lower than-10 dB and well generated gains within the frequency bands 19.7 GHz~20.4 GHz and 19.5 GHz~20.6 GHz respectively,where the maximum gains of the umbrella-shape and polygon prism are greater than 22.0 dBi and 15.0 dBi respectively.Also the measured results mostly agree with the full-wave simulations.Finally,the steerable beams from both reflectors are also verified through the offset feeding.Our approach would be applicable to conformal components on the non-planar platform for the highly directive radiations.2.Curved dual reflecting array antennas based on meta-surfacesA series of conformal reflecting array antennas based on artificial meta-surfaces are proposed on concave,planar,and convex platforms,where the artificial meta-surfaces are devised according to the generalized Snell's law and coated on the reflecting boundaries of the primary and secondary reflectors of the Cassegrain dual reflecting systems,so that the highly directive beams with high aperture efficiencies are well generated with the assistant of optimizations of the field distributions through these meta-surfaces.The full-wave simulations demonstrate the concave,planar,and convex Cassegrain meta-mirrors obtain the maximum gains of 32.7 dBi,33.1 dBi,and 32.0 dBi respectively at the center frequency of 20 GHz,where the corresponding aperture efficiencies are 51%,54%,and 43%.While the traditional Cassegrain design with the same aperture sizes obtain the maximum gain of 33.2 dBi and the aperture efficiencies of 56%.The measured results mostly agree with the full-wave simulations.The concave reflectors have more compact system with much smaller focal length,the planar meta-surface reflectors demonstrate the low profile and easy fabrication,and the convex meta-surface reflectors enables the whole system planted on the curved platform.Finally,we extend these designs into the concave,planar,and convex Gregorian systems through redesigning the phase distributions and structures of the secondary meta-mirrors and also obtain well collimated beams and aperture efficiencies compared to the traditional Gregorian design.3.Curved OAM reflecting array antennas based on meta-surfacesFirstly,the planar OAM Cassegrain meta-mirrors are proposed and a corresponding planar OAM single-meta-mirror is also built for the comparison propose.The reflecting boundaries of the primary and secondary reflectors of the Cassegrain meta-mirrors are coated with units of meta-surfaces devised according to the generalized Snell's law.On the one hand,the field distributions over the primary meta-mirror are evenly distributed with the assistant of the optimizations of the phase distributions through adjusting the secondary meta-mirror.On the other hand,the whole system could generate well converged OAM vortex waves with high directivities,clear helix wave-fronts,and purity vortex numbers through adjusting the phase distributions over the primary meta-mirror.The single meta-mirror is built through removing the secondary meta-mirror of the Cassegrain meta-mirrors and redesign the feeding horn.The full-wave simulations demonstrate Cassegrain meta-mirrors and single-meta-mirror obtain the maximum gains of 23.2 dBi and 22.9 dBi respectively at the center frequency of 20 GHz,and the angular momentum number J reaches 0.9966 and 0.8634 respectively at the distance of 10000 mm from the center of the system.The angular momentum number of Cassegrain design is extremely close to the theoretical value of 1,and the comparing single-meta-mirror still maintain satisfactory OAM vortex waves.Thus the advantages of the high efficient generations of OAM vortex waves from the Cassegrain meta-mirrors are fully verified.Then we extend such a design into conformal concave and convex Cassegrain systems and obtain the excellent syntheses of OAM vortex beams.In addition,we also design concave and convex single-meta-mirrors for comparing using the same method.The full-wave simulations demonstrate concave and convex Cassegrain meta-mirrors obtain the maximum gains of 23.8 dBi and 22.7 dBi respectively at the center frequency of 20 GHz,and the angular momentum number J reaches 0.9899 and 0.9514 respectively at the distance of 10000 mm from the center of the system.While the concave and convex single-meta-mirrors obtain the maximum gains of 23.7 dBi and 22.7 dBi respectively at the center frequency of 20 GHz,and the angular momentum number J reaches 0.8574 and 0.8679 respectively at the distance of 10000 mm from the center of the system.These results demonstrate the high efficient generations of OAM vortex waves from concave and convex Cassegrain meta-mirrors.The three Cassegrain meta-mirrors are fabricated and the corresponding experiments are carried out,where the measured results mostly agree with the full-wave simulations.Finally,the concave case has smaller focal length,the planar case shows compact structure,and the convex case could be planted on curved platform.Our design,obtaining the advantages of high efficient generations of OAM vortex waves with stable angular momentum numbers,has important potential applications in the long-distance propagation for the OAM communications. |
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