Exploring the Potential of a Coaxial Unit Cell: Metalens Antenna Design Based on a Highly Isotropic Metallic Periodic Structure

In this article, we propose a novel glide-symmetric metallic holey unit cell loaded with a coaxial pin and investigate the propagation properties when embedded into parallel-plate waveguides. We demonstrate that the introduction of coaxial loading on the holey unit cell increases the effective refractive index and, together with glide-symmetry, greatly improves the isotropic properties compared to glide-symmetric holey structures. These two properties are desirable when designing graded-index lens antennas. To demonstrate the potential of the new coaxial unit cell, a fully metallic Mikaelian lens antenna is designed and manufactured using the CNC milling technique. The antenna works in the X-band and produces a directive fan beam that can be steered ±30° across the H-plane while keeping the scan loss and sidelobe levels acceptably low. The measured results of the antenna are in good agreement with the simulations.