Overview of multiple antenna designs for handheld devices and base stations

Multiple antennas in conjunction with Multiple Input Multiple Output (MIMO) systems offer significant increases in capacity without increasing transmit power or spectrum and are becoming an integral part of all modern wireless communication systems. For example multiple antenna technology is already used in wireless communication systems such as in IEEE 802.11n, WiMAX and LTE. This paper reviews some recent topologies of multiple antennas for handheld devices and base stations. We will focus on the basic concerns and constraints when designing a multiple antenna system. In particular low mutual coupling between antenna elements should be addressed to attain high radiation efficiency and sufficient MIMO capacity gain. Furthermore the number of ports in the multiple antenna systems works against the devices´ size constraint. Therefore, it is difficult to achieve a very compact antenna solution for handheld devices with more than 4 ports. In contrast, the base station antenna design can sustain tens of ports building on a cubic structure employing both spatial and polarization diversities.