Compact planar 2 × 2 and 4 × 4 UWB mimo antenna arrays for portable wireless devices

A very compact 2 × 2 and 4 × 4 ultra wide band (UWB) multiple input multiple output (MIMO) antenna array with high isolation and polarization/pattern diversity are proposed in this letter. The compact size of antenna with orthogonally polarized elements help in achieving high isolation between elements of the arrays without using any decoupling circuit while maintaining its overall size very compact. The monopole UWB antenna prototype has compact size of 14 × 14 mm2 and enlarged to 2 × 2 array having size of 14 × 31 mm2 and 4 × 4 array having overall size of 31 × 31 mm2. The proposed designs have been fabricated and tested. Measured isolations |S21| are ≤ −25 dB and ≤ −20 dB for 2 × 2 and 4 × 4 arrays, respectively. However, impedance bandwidth |S11| is ≤ −10 dB for both arrays in the range from 3.6 to 10.6 GHz. The simulated, measured and calculated result shows good agreement for its impedance matching, isolation and dual polarization characteristics. Dual polarization improves its diversity performance and compact size improves its spatial multiplexing.