Investigation of Parallel and Orthogonal MIMO Antennas with 2-Notched Structure for UWB Application

Abstract

In order to solve the interference of narrowband in the ultra-wideband (UWB) system, a high isolation of multiple-input multiple-output (MIMO) antenna is investigated in this paper. The MIMO antenna consists of 2 or 4 UWB elements; and each UWB antenna element is a monopole reconstructed with 2-notched slots, a U-shaped and inverted U-shaped slots etched on the monopole patch to achieve notch characteristics in WIMAX and ITU bands. The property of a 2-element MIMO antenna is analyzed firstly, which is put into a same substrate in parallel. Two rectangular branches are located in the middle to reduce the coupling. Then a 4-element MIMO antenna is studied to meet big size space and more application scenarios. Each element is placed orthogonally on the same substrate; and the isolation is implemented by a cross-shaped branch located in the middle of elements. Both MIMO antenna samples have been tested to verify the design. Measured results show that the working bandwidth is 2.45-14.88 GHz and 2.14-14.95 GHz, the isolation is greater than 17 dB and 20 dB, the peak gain is 5.7 dB and 5.9 dB, the max-imum radiation efficiency can reach 96% and 95%, the envelope correlation coefficient is less than 0.02 and 0.05 for the 2- and 4-element UWB MIMO antenna, respectively. They both are with very good omnidirectional characteristic with notched bands such as the WIMAX and ITU, and meet the requirements of the UWB application in most cases.