An Ultra-Wideband MIMO Antenna Design with Improved Performance Using a Hybrid Substrate

Abstract

This research paper presents a compact 2×2 multiple-input multiple-output (MIMO) antenna based on Koch fractal geometry for ultra-wideband (UWB) operation. A defected ground structure (DGS) is applied to the ground plane to enhance the impedance bandwidth, while maintaining a compact antenna structure. Moreover, a hybrid substrate combining FR-4 and RT5880 is integrated to further improve the impedance bandwidth. The design then proceeds with a 2×2 MIMO configuration, where the unit antenna elements are placed orthogonally to support compactness and enhance inter-element isolation. This configuration provides an inter-element isolation greater than 15 dB, while the peak array gain reaches 5.79 dBi within the operating band. The simulated results indicate good MIMO diversity performance characteristics in terms of diversity gain (DG), envelope correlation coefficient (ECC), mean effective gain (MEG), and total active reflection coefficient (TARC). Considering the obtained 1.74–8.76 GHz operating band, the designed antenna can support several wireless applications, including LTE/5G sub-6 GHz bands, Wi-Fi 5/6/6E systems, 5G NR mid-band applications such as n77, n78, and n79, private 5G networks, and C-band communication systems.