A 15–50-GHz Adaptive Beamforming Phased-Array-Fed Lens

This article presents an ultrawideband 15-50-GHz phased-array-fed lens (PAFL) for adaptive beamforming. The PAFL combines a wideband beamformer integrated circuit (BFIC) with multiple complex-weighted feeds to perform adaptive beamforming across a ±52° field of view (FoV). Additionally, a PAFL system is able to produce high-directivity beams using a small number of active elements relative to that of a standard phased array antenna (PAA), dramatically reducing power consumption. To the best of our knowledge, this work presents the widest bandwidth demonstration of a PAFL system, operating from 15 to 50 GHz. Wideband PAFL techniques are demonstrated using a four-element, 15-57-GHz receive array and a 9-in diameter Gradient Refractive INdex (GRIN) lens antenna. The individual basis beams are measured by mechanically offsetting the array along the lens diameter to emulate a physically larger feed array. In this work, a maximum of 32 elements are activated in order to perform adaptive pattern synthesis, which is still less than 1% of an equivalent area phased array ( $1140\lambda _{0}^{2}$ at 50 GHz). Beamforming is demonstrated across the 15-50-GHz band using both analytical expressions and multiobjective optimization pattern synthesis methods to maximize directivity, reduce sidelobe levels (SLLs), improve beam scan (scan loss exponent reduced from 3.2 to 2.6) out to ±52°, and realize adaptive nulling using standard methods for phased arrays. Unique aspects of wideband PAFL systems are discussed and design recommendations are provided for improved operation and performance.