A Compact Four-Element MIMO Antenna with DNG Metamaterial Decoupling Structure for 2.4 GHz Wi-Fi Applications
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Abstract
This paper presents a small four-element MIMO antenna that can work with a frequency of 2.4 GHz and was designed such that it would maximize isolation and radiation efficiency without changing the size of the antenna. Unlike conventional designs of MIMO, which utilize the inter-element spacing of λ/2 to reduce the mutual coupling between the elements, the proposed structure has successfully demonstrated good performance with a smaller inter-element spacing of 15mm. It is worth noting that the center-to-center spacing between the antenna elements is approximately 0.39λ₀ at 2.4 GHz, which is significantly smaller than the ideal λ₀/2 separation typically required for low-coupling MIMO configurations. This reduced spacing naturally increases mutual coupling highlights the necessity of the proposed DNG-based decoupling approach. The very high electromagnetic interaction of this proximity is compensated by embedding between some pairs of selected antennas (ports 2–3 and 1–4) a double-negative (DNG) metamaterial unit cell. These cells inhibit surface-wave propagation and near-field coupling, leading to large gains in isolation and stable impedance properties. The antenna is designed on FR-4 substrate (εr = 4.3, h = 1.6 mm) and its measured performance is to be; S11 = -15.9 dB, S21 = -17.7 dB, S31 = -64.6 dB, S41 = -44.7dB at 2.4 GHz. In addition, a realized gain of 12.68 dBi, radiation efficiency of 87.5% and envelope correlation coefficient (ECC) of 0.0002. The proposed DNG-based MIMO antenna is a good alternative in the future of wireless communication systems in the Wi-Fi and IoT where it is necessary to achieve high isolation in a small physical space.
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