Performance investigation of a dual element IFA array at 3 GHz for MIMO terminals

The distance or separation between antenna elements is small in case of modern compact Multiple-Input Multiple-Output (MIMO) terminals and this is the most critical parameter affecting mutual coupling. Mutual coupling has been a subject of interest in MIMO communications, since it influence the channel matrix, and thus, the capacity of the MIMO system. Although it is a well known subject in antenna theory it has not been studied in as much detail from the MIMO terminals perspective. In this paper the impact of different antenna placements (both position and orientation) inside the MIMO terminal on the mutual coupling between two antenna elements and hence their diversity performance is evaluated and investigated in details. The antenna element employed is a pair of inverted-F antennas (IFAs) working at 3 GHz and is placed in various orthogonal and parallel configuration on a PCB ground plane with dimensions that are comparable with a mobile phone. The optimal position and orientation for the IFA antennas inside the MIMO terminal with low mutual coupling which leads to good diversity performance is addressed. It is found that some configurations are capable of providing high isolation between the IFA array elements. The EM simulation was carried out by using the Computer Simulation Technology (CST) Microwave Studio package, which utilizes the finite integral technique (FIT) for electromagnetic computation.