Wideband Circularly Polarised Compact MIMO Antenna With Enhanced Isolation for RF Energy Harvesting

A wideband circularly polarised compact MIMO antenna with enhanced isolation for RF energy harvesting is proposed. The antenna realises 42% impedance bandwidth and 1.5% axial ratio bandwidth, with a bandwidth overlap of 0.99. Circular polarisation improvement is achieved through ground-plane modification based on characteristic mode analysis, while a plus-shaped decoupling structure mitigates mutual coupling. The MIMO array, composed of four orthogonally oriented radiating elements, ensures broad angular coverage and polarisation diversity. The antenna operates from 4.0 to 7.5 GHz, with diversity performance quantified through envelope correlation coefficient, diversity gain, channel capacity loss, and total active reflection coefficient, demonstrating robust MIMO behaviour.