A Compact 2-Element Symmetrically Fed MIMO Antenna with a Ground Isolation Stub for Ultra-Wideband Communication Systems

In this paper, a compact multiple-input multiple-output (MIMO) antenna, with a ground isolation stub for ultra wideband (UWB) communication systems, is presented. The proposed design is based on two symmetrical semi-circular patches, fed by stepped‐impedance microstrip lines, on the top side of the substrate, and a partial ground plane with two symmetrical large rectangular-shaped defected ground structure (DGS) units with a stub in between, and two symmetrical thin rectangular-shaped DGS units, on the bottom side. The two radiating elements are fed using a symmetrical feeding technique for future MIMO antenna systems. The 2-element UWB MIMO antenna with a simple structure and small size of 24 × 35 mm² is printed on FR4 substrate material. This study has resulted in an impedance bandwidth from 3.3 to 20 GHz which insures that the UWB spectrum is properly covered. In addition to that the elements are well isolated due to the fact that the isolation coefficient is smaller than −20 dB for the whole range of frequencies. The proposed structure exhibits stable omni-directional patterns and nearly bidirectional patterns in both E- and H-planes with an increasing gain across the operation bandwidth. An acceptable agreement between measured and simulated S-parameters is obtained.