Characteristic mode analysis applied to reduce the mutual coupling of a four-element patch MIMO antenna using a defected ground structure

A multiple-input-multiple-output (MIMO) microstrip patch antenna array of four elements is proposed to cover the 5.8 GHz WLAN band. The characteristic mode analysis is carried out to design a defected ground structure that improves the MIMO performance without impacting negatively the radiation characteristics of the four-element array. Simulations and measurements demonstrate that the implemented prototype reaches a maximum mutual coupling of -32 dB and a gain-per-element of 5.3 dB with good MIMO attributes, surpassing many other proposals in the antenna literature: maximum envelope correlation coefficient of 0.0001, diversity gain very close to 10 dB, capacity loss (C-loss) near to 0.0023 bps/Hz at the resonant frequency, multiplexing efficiency (eta(muxij)) of 0.935, and a total active reflection coefficient weakly dependent on the excitation phases. The presented design is proposed for operation on the IEEE 802.11a/n standard.