High Gain And Wide-angle Scanning Lens Antenna And Array

With the development of communication technology,the requirements of antenna gain and beam coverage are also increasing.Although traditional antenna array could achieve high gain radiation and beam scanning,there are some problems such as complexity and limited scanning range.Due to the specific gradient index distribution,gradient index lens can control the propagation of electromagnetic wave and consequently realize high gain radiation and wide angle scanning.The gradient index lens has received more and more attention for its special advantages compared with the traditional array.In recent years,with the development of metamaterial and 3D printing technology,the construction of gradient index lens become more convenient and precise.Meanwhile,the proposed transformation optics makes it possible to design new types of gradient index lens with the specific functions.Therefore,the gradient index lens has become a current research hotspots.This paper mainly studies the lens antenna with high gain radiation and wide-angle beam scanning functions.Firstly,based on the high directivity and off-axis characteristics of Half Maxwell Fish Eye Lens(HMFL),discrete beam scanning can be achieved by moving the feed or switching the feeds located at the different positions.In addition,the field distribution of HMFL has been obtained by the ray tracing method and the reason for low aperture efficiency of HMFL is analyzed.A method by cutting the edge part of HMFL is proposed to increase the aperture efficiency.Meanwhile,the shape of HMFL is transformed from the traditional hemisphere to cylinder based on the transformation optics method.By this method,the HMFL' profile is reduced with the electromagnetic performance unchanged.Secondly,a high gain and wide angle beam scanning antenna based on the single Luneburg lens is studied.According to the focusing and spherical symmetry characteristic of the Luneburg lens,beam scanning can be realized by changing the feed position on the lens surface.Based on the same characteristics,a feed array is arranged along the spherical surface of the Luneburg lens to realize discrete beam scanning within ±60° by switching the elements of the array.Besides,the problems is analyzed,which exist in the construction of cylindrical Luneburg lens by means of the transformation optics method.A method of transforming the lens together with the surrounding free space is proposed to improve the gain of the transformed cylindrical Luneburg lens.Thirdly,high gain and wide angle scanning array composed of multiple Luneburg lenses is studied.On the premise of ensuring high gain and wide angle beam scanning,a single large size Luneburg lens antenna can be replaced by multiple small size Luneburg lens array,to reduce the profile and suppress the material loss.Here,the small size Luneburg lenses are of prolate shape to abate the occlusion effect between the lenses.Meanwhile,the relationship between the number of feed elements and the beam coverage capacity is analyzed.For the subarray composed of two adjacent feeds,the amplitude control method is used to realize small angle scanning.And the half power beam coverage in large angle range can be achieved with few feeds,by combining the small angle scanning by subarray with the discrete beam scanning by multi feeds.Finally,an improved Luneburg lens antenna with higher aperture efficiency is studied.The electric field distribution of the Luneburg lens is analyzed by the ray tracing method,and the reasons for the low aperture efficiency of the traditional Luneburg lens is realized.For the small size Luneburg lens(Feed size L/lens diameter D>0.1),the method of multiplying a modify factor into the relative permittivity distribution of Luneburg lens is proposed to improve the aperture efficiency.This method is also extend to the ellipsoid Luneburg lens to construct an improved ellipsoid Luneburg lens array antenna with±63°half power beam scanning range.For the large size Luneburg lens(Feed size L/lens diameter D ?0.1),a method of cutting the edge part of the Luneburg lens is proposed to increase the aperture efficiency.