Efficient Isolation of an MIMO Antenna Using Defected Ground Structure

To implement efficient isolation between units of a multi-input multi-output (MIMO) antenna, a defected ground structure (DGS) has been investigated. An antenna with two elements operating at 5.8 GHz and fed by coaxial is considered. To reduce mutual coupling between the elements, a zigzag groove is inserted into the center of two elements formed as a DGS. To verify this design, a scattering matrix was tested, such as reflection coefficient S(11)and transmission coefficient S(21)between two element ports. Meanwhile, radiation pattern, current distribution, envelope correlation coefficient (ECC), and diversity gain of the antenna were simulated and measured. The results showed that the mutual coupling was reduced by 28.8 dB when a DGS was used, and the ECC was less than 0.02. Owing to these good performances, each antenna element can operate almost independently, and this MIMO antenna can be efficiently applied to the narrow band Internet of Things system.