Insulation Improvement in MIMO Antenna Using ENG Metamaterial Decoupling Structure

Abstract

This work presents the design and performance enhancement of a compact MIMO antenna operating at 60 GHz for millimeter-wave 5G communication systems. The pri- mary objective is to improve isolation between closely spaced antenna elements using an ENG (Epsilon Negative) metamaterial decoupling structure. The proposed single antenna element achieves a reflection coefficient of S11 = −28.51 dB, a realized gain of 7.17 dBi, and a radiation efficiency of 92.68% at 60 GHz. A 2 × 1 MIMO antenna is then designed with an edge-to-edge spacing of 1.4 mm (0.28λ). Without isolation, the mutual coupling reaches approximately −18 dB. An ENG metamaterial unit cell is designed and char- acterized, exhibiting negative permittivity at the operating frequency. After integrating the ENG structure, the transmission coefficient S21 is significantly reduced from −18 dB to −50 dB, representing an isolation enhancement of 32 dB. Consequently, the Envelope Correlation Coefficient (ECC) remains approximately 4.06 × 10−8 , the Diversity Gain (DG) reaches 9.99 dB, the Channel Capacity Loss (CCL) remains below 0.4 bits/s/Hz, and the Total Active Reflection Coefficient (TARC) stays under −10 dB. These results confirm that the proposed ENG-based decoupling structure effectively suppresses mutual coupling and enhances MIMO performance, making it a suitable candidate for 60 GHz millimeter-wave communication applications.