Multibeam dielectric lens antenna for 5g mobile base station

Abstract

The introduction of fifth-generation (5G) mobile communication technology has new features such as millimetre wave operation, small cell size and multibeam base station antenna to meet massive multiple-input multiple-output (MIMO) requirements. The introduction of fifth-generation (5G) mobile communication technology has new features such as millimetre wave operation, small cell size and multibeam base station antenna to meet massive multiple-input multiple-output (MIMO) requirements. At millimetre wave, the base station antenna size is expected to be less than 30 cm, and aperture antennas such as the reflector and the dielectric lens antenna can be among the alternatives to replace the present array antenna. Based on previous works, the dielectric lens antenna was designed to produce excellent multibeam radiation patterns as compared to the reflector antenna. Many lens antennas have been reported for various applications such as airborne radar and vehicle’s collision avoidance system. For base station application, the lens antennas with small thickness and curvature are required for light weight and ease of installation. The main objective of this research is to propose a new lens design method for thin and small curvature antenna and ensure its multibeam characteristics. By developing the geometrical optics algorithm for lens shaping method in MATLAB software, the conventional Aperture Distribution Condition (ADC) and the Abbe’s Sine Condition (ASC) are designed to ensure the accuracy of the developed algorithm. In order to achieve the thin lens and small curvature structure, a newly proposed design method, namely Straight-Line Condition (SLC) lens at designed frequency of 28 GHz and material with dielectric constant, εr of 4 was developed. At the lens size of 10 cm antenna with ratio focal length-to-diameter, F/D=1, the SLC lens structure provides thickness of 1.38 cm as compared to ADC and ASC with thickness of 1.7 cm and 1.48 cm, respectively. Multibeam radiation patterns of ADC, ASC and SLC were compared by using electromagnetic simulator FEKO. Good multibeam radiation patterns for SLC is ensured for scanning beam angle from 0° to 42.6°. To determine the optimum feed positions for multibeam performances, the focal region ray tracing was conducted in receiving mode by the Ray Launching-Geometrical Optics (RL-GO) solver of FEKO simulator. New feed positions locus for SLC was obtained and compared to ADC and ASC. For the practical application to install base station pole, the cylindrical structure of SLC lens antenna was designed at the F/D ratio of 0.6 and polycarbonate material with dielectric constant, εr of 2.9 was selected. The practical size of cylindrical height of lens antenna is 20 cm and the cylinder diameter is 29 cm with thickness of about 5.13 cm. New feed position locus for SLC cylindrical structure was obtained at F/D ratio of 0.6. From the near field distribution, phase constant and adequate amplitude distribution on the aperture plane is ensured. Fan beam radiation pattern was produced for the cylindrical lens. In the vertical plane, multiple beams radiation pattern was achieved. The beamwidth of fan beam is 45° and vertical beam is 3.28° with maximum antenna gain of 22.98 dBi. Good multibeam radiation patterns are obtained for wide scanning beam ranging from 0° to 47.1° in the vertical plane. Gain reduction is 6.56 dBi. As a result, the new proposed of cylindrical SLC dielectric lens antenna is suitable for the use of 5G multibeam base station application.