A Novel Low-Profile Folded Flat Luneburg Lens Antenna for 5G mm-Wave Applications

This paper proposes a novel low-profile folded flat Luneburg lens antenna (LLA). The design of the antenna is as follows: Firstly, based on the principles of transform optics (TO), the conventional spherical LLA is compressed into a flat cylindrical configuration. Then, utilizing the HFSS-matlab optimization tool, the flat lens is optimized and discretized into a six-layer structure. Finally, by adding polarization-conversion reflective elements around the feeds and applying a polarization filter to the underside of the flat lens, the distance between the lens and feeds can be reduced to $1 / 3$ of its original value. The overall profile height of the proposed folded flat LLA is only 25.2 mm, with a height-to-diameter ratio of 0.42. In addition, by turning on/off the feed components, the proposed antenna can achieve one-dimensional beam scanning with a coverage range of ± 20° and a scan loss of only 2 dB at 28 GHz. The simulated gain of the broadside beam is 20.55 dBi, and the corresponding aperture efficiency is $36.65 \%$. The proposed folded flat LLA has advantages such as low profile, wide beam scanning range, low cost, flatness and easy manufacturing, making it very suitable for 5G millimeter-wave wireless communication.