Reduction of the grating lobes in Luneburg lens arrays

Mobile satellite communication systems suitable for installation on moving vehicles are increasingly in demand [1]-[3]. One of the main requirements for such systems is low-profile in order to prevent intolerable drag and air-stream turbulence. A low profile Ku-band antenna system based on a four-element Luneburg lens array (LLA) was presented in [3] where the reduction in height is achieved by using a ground plane and by increasing the number of elements at the expense of increased diameter of the array. However, using an array of elements has an inherent problem of grating lobes [4]. This problem is particularly difficult in an array of lenses since the minimum array spacing is limited by the lens size and generally it is of the order of several wavelengths. High grating lobes in the radiation pattern limit the usefulness of the lens array and their reduction is critical. So far, the results for the expected grating lobes in an array of Luneburg lenses have not been reported in the literature. Our aim is to study the grating lobes in a LLA as a function of the number of lenses in the array and also as a function of the spacing between the lenses. We present simulated results for the radiation patterns of two arrays using three and four Luneburg lenses, respectively, and show how removing part of the outer shells of the Luneburg lens and decreasing the element spacing can reduce the grating lobe level.