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 that 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 GRadient INdex (GRIN) lens antenna is designed, fabricated, and measured in both far-field and near-field chambers. The antenna functions as intended from 14 to 40GHz 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.