Simple ultra‐wider‐bandwidth MIMO antenna integrated by double decoupling branches and square‐ring ground structure

A small and simple four-port ultra-wideband multiple input multiple output (UWB-MIMO) antenna is designed in this letter. Each element of the designed antenna is composed of a circular patch, two smaller parasitic U-shaped patches, a microstrip feed line, and a common square-ring ground plane. To increase impedance bandwidth and reduce the size, this letter introduces the circular patch, two smaller parasitic U-shaped patches, and the common square-ring ground structure with multislits and the truncated corners. On the other hand, all the elements are identical and symmetrical, and neighboring elements are orthogonal to each other for improving the isolation. Furthermore, the double decoupling branches are added on diagonal position of the common square-ring ground to further enhance the isolation and broaden the bandwidth. Therefore, the proposed UWB-MIMO antenna is designed by using a novel and effective method of integrating the symmetric layout, orthogonal structure, four-directional double branches decoupling, parasitic structure, truncated corners, and multislit techniques. Thus, the designed UWB-MIMO antenna has the small physical size of 40 mm x 40 mm and obtains the ultra-wider bandwidth of 3.0 to 18.0 GHz, higher isolation (>20 dB), smaller envelope correlation coefficient (rho(e) < 0.03), and higher multiplex efficiency (eta(mux) > -3.0 dB). Besides, the UWB-MIMO antenna also achieves the acceptable peak realized gain, and stable radiating characteristics. Consequently, the designed antenna can be used for most UWB-MIMO applications.