A Study of Decoupling Method Using Parasitic Elements for Two Planar Inverted-F Antennas

In recent years, multiple-input multiple-output (MIMO) applications are known as a potential technique for enhancing the system performances with large capacity and high-speed transmission, and play a major role in developing the next generation communication [1] . This technique is applied for not only base station but also mobile handset terminal. For mobile handset terminal, because of the limited space for antennas installing, it is necessary to space the MIMO antennas closely on the same ground plane. However, the strong mutual coupling occurs between them and adversely affect the total antenna efficiency. For this reason, reduction of mutual coupling between MIMO antennas is required. So many decoupling solutions have been proposed using various arrays of conventional antenna element. Among them, we focus on the simplicity of the decoupling method using bridge line (BL) to connect directly antennas [2] . When antenna elements are connected directly by a BL, strong mutual coupling can be reduced, but the resonant frequency shifts to a different frequency. Hence, to shift the resonant frequency toward the desired frequency, the original size of the antenna elements must be adjusted. This is disadvantageous if the method is applied in cases where the design conditions render it difficult to connect the antennas directly or adjust the original antenna size. Therefore, to easily reduce mutual coupling in such a case, a decoupling method that does not require both connecting antennas directly and adjusting the original antenna size is necessitated. In this study, we propose a novel decoupling method using parasitic elements (PEs) connected by the BL.