High-efficiency, Wideband GRIN Lenses with Intrinsically Matched Unit-cells

Abstract: We present an automated design procedure for the rapid realization of wideband millimeter-wave lens antennas. The design method is based upon the creation of a library of matched unit-cells which comprise wideband impedance matching sections on either side of a phase-delaying core section. The phase accumulation and impedance match of each unit-cell is characterized over frequency and incident angle. The lens is divided into rings, each of which is assigned an optimal unit-cell based on incident angle and required local phase correction given that the lens must collimate the incident wavefront. A unit-cell library for a given realizable permittivity range, lens thickness, and unit-cell stack-up can be used to design a wide variety of flat wideband lenses for various diameters, feed elements, and focal distances. A demonstration GRIN lens antenna is designed, fabricated, and measured in both far-field and near-field chambers. The antenna functions as intended from 14 GHz to 40 GHz and is therefore suitable for all proposed 5G MMW bands, Ku- and Ka-band fixed satellite services. The use of intrinsically matched unit-cells results in aperture efficiency ranging from 31% to 72% over the 2.9:1 bandwidth which is the highest aperture efficiency demonstrated across such a wide operating band.