I. Introduction
Aperture efficiency is one of the critical parameters in the design of antenna array as it measures how efficient the array utilizes its aperture for radiation purpose. In particular for large scale antenna array operating at high frequency bands, i.e., the millimeter-wave band, high aperture efficiency becomes more demanding because the losses associated becomes more significant. This paper presents a Huygens antenna array design that achieves the aperture efficiency close to the ideal 100% at 28 GHz in the Ka band. Almost the entire aperture is utilized to contribute to the co-polarized radiation thanks to the complementary nature of the Huygens radiation. Considering apply the array to wireless applications requiring low sidelobe levels as the object detection system [1], tapered excitation scheme has been applied to the array to achieve all sidelobe levels less than - 20 dB. A full-metal prototype with seamlessly integrated waveguide-based feed network was fabricated and measured, the realized aperture efficiency is the highest among all previously reported large scale antenna arrays [2]– [10] with low sidelobe levels.