Low correlation MIMO antenna for LTE 700MHz band

A key feature of upcoming 4G wireless communication standards is multiple-input-multiple-output (MIMO) technology. To make the best use of MIMO, the antenna correlation between adjacent antennas must be low (<; 0.5). In this context, we propose a new correlation reduction technique suitable for closely spaced antennas (distance, d <; λ/40). This technique reduces mutual coupling between antennas and concurrently uncorrelates the antennas´ radiation characteristic by inducing negative group delay in the target frequency band. The validity of the technique is demonstrated with a USB dongle MIMO antenna designed for LTE 700MHz band. Measurement results show that the antenna correlation is reduced more than 37% using the proposed technique.