A Cylindrical Lens Antenna With Extremely Flat Beams

This paper presents an extremely flat-beam cylindrical lens antenna with a 180 mm ($36~\lambda$ ) diameter lens at 60 GHz. The parameters of lens antennas in the horizontal plane i.e. dielectric constants, radii, and focal length are optimized to widen beams in the vertical plane while obtaining pencil beams in the horizontal plane. The optimization procedure consists of a theoretical method and differential evolution (DE) algorithm. This beam-widening idea is analyzed and proved to be feasible owing to cylindrical apertures, which is quite different from the results of antennas with planar apertures. Then, the permittivity distribution which results in an extremely flat beam is investigated and shows a novel S-shape rather than following either the law of modified Luneberg lens or the Luneberg's Law. Finally, the proposed lens antenna is fabricated and measured. At the design frequency of 60 GHz, the measured 3-dB E- and H-plane beamwidths separately are 100.4° and 2.3°. As compared to the gain peak, the measured and simulated gain drop at ±60° in the E-plane are less than 4 dB and 5 dB, respectively. Measured results show good agreements with the simulated results, thus validating the extremely flat beam of the proposed lens antenna and the effectiveness of the optimization procedure.