Wideband and High-Efficiency Parallel-Plate Luneburg Lens Employing All-Metal Metamaterial for Multibeam Antenna Applications

A parallel-plate Luneburg lens (LL) based on all-metal metamaterial is presented in this article. To achieve the required refractive index distribution of the LL, an all-metal unit cell with a separated cuboid is proposed, whose height is related to its refractive index. This inserted cuboid is attached to neither the top plate nor the bottom plate of the parallel plate. Compared with traditional bed of nail design, the proposed metamaterial unit cell exhibits a wider bandwidth. The operation principle of such a unit cell is investigated using the transverse resonance technique. To construct the all-metal metamaterial LL into one body, a cruciform cuboid is added to each unit cell, such that adjacent unit cells can connect to each other. Based on the designed metamaterial LL, a multibeam antenna is developed by providing seven inputs, which can generate seven predefined beams. Several parts of the prototype are separately fabricated and assembled, and good agreement is observed between simulation and measurement. The designed LL-based multibeam antenna has several advantages, including wide bandwidth, high aperture efficiency, and high radiation efficiency.