Compact multiple-input–multiple-output antenna using quasi-self-complementary antenna structures for ultrawideband applications

A compact multiple-input-multiple-output (MIMO) antenna with a very small size of only 21 × 38 mm² is proposed for ultra-wideband (UWB) applications. It consists of two quasi-self-complementary antenna (QSCA) elements with an inverted T-shaped common ground plane. The QSCA elements are the mirror images of each other, having a half-circular conductor patch on one side of the substrate and a slot with the complement of the half-circular shape on the other side. To reduce mutual coupling between the two QSCA elements, two rectangular slots are cut symmetrically on the ground plane between the two elements. Simulation and measurement are used to study the performance of the MIMO antenna in terms of reflection coefficient, isolation between the two ports, radiation pattern, realised gain, efficiency and envelope correlation coefficient. The results show that the MIMO antenna has a bandwidth from 3.1 GHz to more than 10.6 GHz with a mutual coupling of less than -15 dB and a correlation of less than 0.1, respectively, making it a good candidate for portable UWB applications.