Design of a Compact MIMO Antenna Using Coupled Feed for LTE Mobile Applications

A compact multi-input multi-output (MIMO) antenna with a coupled feed structure for 4th generation (4G) handsets is proposed for operation in long-term evolution (LTE) band 13 (0.746GHz-0.787GHz). The MIMO antenna consists of two symmetrically distributed identical antenna elements. The size of each element is limited to 20 mm x 10 mm x 5 mm(lambda(0) = 392 mm at 0.765 GHz), and the separation between different elements is minimized to 15 mm. Each antenna element contains a Z-shaped coupled feed strip and a simple folded monopole-type radiating element. The simple folded radiating element supports two monopole modes (first order) excited at adjacent frequencies to achieve broadband performance. The coupled feed strip effectively modifies impedance matching and maintains good isolation. The proposed antenna has a 6 dB return loss bandwidth of 55 MHz (0.735 GHz-0.79 GHz) and isolation above 12 dB without the use of an additional isolation enhancement element. Moreover, the envelope correlation coefficient (ECC) is maintained below 0.5 over the designed frequency band.