A compact broadband MIMO antenna for mobile handset applications

As the original multiple-input multiple-output (MIMO) paradigm assumed, the use of NT antennas at the transmitter and NR antennas at the receiver can achieve the capacity growth linearly with min (NT, NR) through an independent and identically distributed (i.i.d.) Gaussian MIMO channel [1]. But poor diversity in the propagation multipath and mutual coupling between antenna elements will cause the sub-channel correlation, which subsequently leads to a loss of channel capacity as compared to the ideal i.i.d. Gaussian MIMO channel. Recently, the advantage of omni-directional antenna elements in MIMO applications has been proved in [2], for the ability of forming eigen-beams from any direction necessary in a rich multipath environment. But how to pack omni-directional antennas into a portable device is still an issue since the correlation becomes more serious for the short distance between the array elements. In this paper, we demonstrate a planar antenna array realized with two broadband omni-directional elements [4]. This array realizes a good performance under MIMO situations with low mutual coupling (<-11dB) and low correlation coefficient (≤-15 dB) in a very wide bandwidth (more than 40% at about 2.1GHz) and a compact size (50mm×67.2mm×0.254mm). That is more compactable than the array demonstrated in [1] with a wider bandwidth than the arrays shown in [1], [5], and [6].