Enhanced isolation with defected ground structure in MIMO antenna

A defected ground structure (DGS) for improving isolation between four ports in a collocated multiple-input-multiple-output (MIMO) antenna is proposed. Isolation improvement by 7 dB is achieved by reducing surface waves within the dielectric substrate. Mutual coupling values as low as -25 dB are obtained along both the E- and H-planes. The MIMO antenna includes a square patch antenna surrounded by a square ring patch antenna with the DGS etched in the form of a square ring. The DGS effectively suppresses the cross-polarisation levels for all radiating modes. The design and effectiveness of the DGS in improving isolation for a fabricated 4-port antenna are discussed.