Dual-Band Co-Polarized MIMO Patch Antenna With Shared Aperture and High Isolation Using Charge Redistribution Stub

This paper introduces a dual-band co-polarized MIMO patch antenna utilizing a charge redistribution stub (CRS) technique to achieve high port-to-port isolation within a shared-aperture design. The proposed approach leverages I-shaped CRS (I-CRS) and L-shaped CRS (L-CRS) to independently control modal resonance and field redistribution, achieving high isolation and broadside radiation across two frequency bands. First, theoretical isolation conditions are derived, demonstrating that equal-magnitude, anti-phase mode pairs are required for effective decoupling. Metallic vias are then employed to establish a TM₂₁-TM₂₂ mode pair for isolation in the higher band, while I-CRS and L-CRS structures are introduced to form a TM₀₁-TM₀₄ mode pair and correct radiation patterns, ensuring dual-band functionality with co-polarization. A prototype was designed, fabricated, and tested, showing excellent performance with isolation exceeding 20 dB, impedance bandwidths of 3.0% and 9.2%, and peak gains of 7.6 dBi and 9.3 dBi across the two bands. The measured envelope correlation coefficient (ECC) values remain below 0.1, confirming strong MIMO diversity performance. Therefore, the proposed MIMO antenna achieves dual-band operation in a shared aperture configuration through a charge redistribution mechanism, while maintaining high port-to-port isolation and demonstrating stable broadside radiation characteristics with low cross-polarization levels, making it a strong candidate for next-generation wireless systems.