Design and performance evaluation of multiband MIMO antennas

Recently various wireless local area network (WLAN) technologies have been unified by means of multiband antenna. The challenge is to optimize the size of the multiband antenna for its inclusion in a small hand held terminal, while maintaining its performance characteristics. The challenge is further intensified as the multiple element antenna (MEA) are considered for compact diversity and multiple input multiple output (MIMO) terminal devices. MIMO is considered as a solution to overcome the problems of low data rates and maximize the channel bandwidth. Moreover, it also addresses the problems of multipath fading. Unfortunately, in real and robust environments there is a tradeoff between number of MEA and MIMO performance. This is primarily due to the mutual coupling between the antennas. In this paper, design of multiband MIMO antennas and its performance evaluation has been proposed for the portable wireless communication terminals. To study the effects of mutual coupling, the two-element antenna has been arranged into four MEA configurations. The Meander-Koch monopole antenna element has been used in the design of MEA. The single element meander-Koch monopole antenna covers the entire IEEE 802.11 a/b/g standard. However, due to the lack of an isolation mechanism and effective spatial/pattern diversity technique(s), all the MEA configurations depict poor isolation between their ports. Moreover, a shift in resonant frequency bands has also been noticed.