A meta-surface antenna array decoupling (MAAD) design to improve the isolation performance in a MIMO system

In this paper, a design to reduce the mutual coupling between two closely MIMO antennas is presented. A metasurface superstrate consisting of periodic circular split ring resonator (CSRR) elements is placed above the coupled two-element patch antennas to improve the isolation performance. The propagation of the electromagnetic wave from antenna 1 to antenna 2 causing mutual coupling will be blocked since the loading of metasurface, which can be considered as a negative-permeability medium. First, the size of the CSRR element is determined by properly designing the range of negative permeability in the desire band. Thereafter, a decoupled MIMO array with a high isolation performance is realized with an intolerable matching curve. Then, some measures are employed on each patch to enhance the matching performance, such as etching slots and loading short probes on the patches. Next, two prototypes for the coupled and decoupled arrays are fabricated and measured to verify the improvement of the isolation performance. Measured results show that the value of |S21| for the decoupled array has been greatly improved from -8 dB to less than -20 dB within the entire working band of 5.58-6.0 GHz. Meanwhile, the match bandwidth of |S11| < -15 dB for the decoupled array is approximately 420 MHz, which has also been improved in the desire band compared with the coupled array. In addition, the measured gains for the decoupled array are improved by approximately 1.8 dB as compared to the coupled array, whereas the efficiencies are increased by 16% which is higher than the coupled array. Moreover, the envelope correlation coefficient (ECC) for the decoupled array is reduced from 0.17 to 0.06 within the entire band of interest. Therefore, all measured results demonstrate that the proposed MAAD design is a good candidate for the improvement of MIMO antenna arrays.