A nonplanar quad-element UWB-MIMO antenna with graphite sheet to increase the isolation

A nonplanar quad-element ultra-wideband (UWB) antenna for four-port multiple-input-multiple-output (MIMO) is designed in this paper. The MIMO antenna element is covered in the surface of polystyrene block with a cylindrical hole, and a thin graphite sheet which fixed with a polystyrene cylindrical block is fabricated in the column hole. This element of the antenna has a most compact size (18*20mm
²
). The round monopole antenna elements with coplanar waveguides (CPWs)-fed are printed on the FR4. An inverted L-shaped structure with rectangle-shape slots provides the lower levels of the return loss. By the simulation, the return loss is lower 15dB over the range from 3 to 11GHz, which broadband impedance is matched. In addition, the three-dimensional (3-D) UWB-MIMO system provides high isolation between elements. Moreover, the envelope correlation coefficient is calculated, which shows good MIMO performance.