Approach for improving inter-element isolation of orthogonally polarised MIMO slot antenna over ultra-wide bandwidth

With the increasingly multiple-input multiple-output (MIMO) applications in ultra-wideband (UWB) communication systems, antenna researchers face big challenges in designing compact operational geometries that meet the essential demand of achieving high isolation among antenna elements over the ultra-wide operating bandwidth. Disposed antenna elements orthogonally are seen to be the most common methodology to reduce mutual coupling of MIMO antenna by exploiting polarisation diversity performance. In such configuration, the mutual coupling mainly depends on the inter-element spacing. which it may not be in line with the compact structure. In this Letter, taking the advantages of symmetry of planar UWB antennas, asymmetric feeding scheme miniaturising technique is utilised to improve the inter-element isolation of a reference MEMO antenna made up of four previously designed slot antenna elements, closely-disposed orthogonally. Analytical results have validated the design concept and the improved MIMO antenna using the halved-chopped elements, showing good performance in terms of impedance matching, isolation, radiation features, signal correlation, and system fidelity factor.