Direction-independent and self-reconfigurable spherical-cap antenna array beamforming technique for massive 3D MIMO systems

Abstract

Massive 3D MIMO beamforming is very important for 5G and beyond networks to improve the system performance and capacity. However, 3D beamforming capabilities are limited by the antenna array configuration. Therefore, in this paper, an efficient self-reconfigurable spherical-cap antenna array and 3D beamforming technique are proposed to provide direction-independent symmetrical beam patterns with low sidelobe and backlobe levels. The symmetric beam generation is achieved by forming electronically steerable spherical-cap array which is extracted from a uniform spherical antenna array and is continuously reconfigured so that its axis of symmetry is maintained the same as the mainlobe direction. On the other hand, the antenna elements in the spherical-cap array are further processed to minimize the sidelobe and backlobe levels by using an optimized exponential decaying feeding profile in the form of $e^{{ - \alpha \left( \rho \right)^{\beta } }}$. Assuming isotropic antenna elements with negligible mutual coupling, the generated beam power patterns are examined where simulation results show that a sidelobe level of − 30 dB and backlobe level of less than − 16 dB relative to the mainlobe level can be achieved. Also, the variation in the 3 dB beamwidth with the mainlobe direction has been examined for 10,000 uniformly random generated mainlobe directions at different array sizes where it is found that the beamwidth is almost constant with less than 1% variation especially for large sized arrays.