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A Novel Isolation Improvement Technique for Wideband MIMO Antenna Systems

In this paper, a novel technique for improving element isolation in wideband multiple-input-multiple-output (MIMO) antennas in a parallel configuration is presented. Our methodology is based on ground plane alterations, in particular, introduction of an n-section rectangular slit below the feed line combined with a multi-stage EM-based adjustment of antenna geometry. The technique is demonstrated using a representative set of four wideband MIMO antennas with an intention to analyse the relevance of the approach for various radiator geometries. To maintain a compact antenna size while ensuring acceptable electrical performance, rigorous EM-driven optimization is carried out involving all antenna geometry parameters. The numerical results indicate a clear advantage (in terms of isolation improvement) of increasing the number of the slit sections but also a saturation effect beyond n = 2. The antenna optimization process aims at satisfying two performance specifications: reflection |S11| ≤ −10 dB, and isolation |S21| ≤ −20 dB, both within the entire operational bandwidth. Other important figures obtained for the optimized designs, such as Envelop Coefficient Correlation (ECC < 0.005), diversity gain (DG > 9.99 dB), and total efficiency approximately > 80%, confirm suitability of the proposed technique in the context high-performance compact MIMO antenna design.