Abstract
This article presents a compact, planar, quad-port ultra-wideband (UWB) multiple-input-multiple-output (MIMO) antenna with wide axial ratio bandwidth (ARBW). The proposed MIMO design consists of four identical square-shaped antenna elements, where each element is made up of a circular slotted ground plane and feed by a 50 ohm microstrip line. The circular polarization is achieved using a protruding hexagonal stub from the ground plane. The four elements of the MIMO antenna are placed orthogonally to each other to obtain high inter-element isolation. FR-4 dielectric substrate of size 45 x 45 x 1.6 mm(3) is used for the antenna prototype, and a good agreement is noticed among the simulated and experimental results. The proposed MIMO antenna shows 3-dB ARBW of 52% (3.8-6.5 GHz) and impedance bandwidth (S-11 <= -10 dB) of 144% (2.2-13.5 GHz).