A high-isolation quad-port MIMO antenna with self-coupled defected ground structure for sub-6 GHz wireless applications

A compact quad-port multiple-input multiple-output (MIMO) antenna is proposed for broadband sub-6 GHz wireless communication applications. The antenna is implemented on a low-cost FR-4 substrate with a thickness of 1.6 mm and relative permittivity of 4.4, occupying an overall area of only 36 × 55 mm². The proposed antenna is designed by combining three main contributions of an orthogonal radiator with a slit-loaded resonator, a branch shorted in the ground plane, and an interconnected defected ground structure (IC-DGS) to enhance the bandwidth while reducing the inter-element coupling. By employing the design process, multiple resonance modes are combined to achieve an effective, continuous wideband impedance range from 2.10 GHz to 4.55 GHz (S 11 < − 10 dB) while maintaining excellent port-to-port isolation characteristics, thereby enabling the antenna to be utilized in sub-6 GHz broadband wireless communication applications, which makes it very attractive to modern multi-standard wireless communication systems (covering LTE Band 40 as well as WLAN/WiMAX and 5G NR Bands n77, n78, and n79), while simulated and measured data show excellent correlation in terms of performance. This has been achieved by maintaining minimal S 31 < -26.05 dB and S 21 < -35.10 dB within the operational band. Furthermore, a radiation efficiency exceeding 85% is maintained while preserving stable gain characteristics. Diversity performance is verified through an ECC below 0.30, DG close to 10 dB, and CCL below 0.025 bits/s/Hz, indicating excellent MIMO operation. The proposed quad-port MIMO antenna is a promising candidate for the next generation wireless platform (IoT device, smart terminal, wireless access point, base station, and vehicular communication system); it has a compact design, a low-profile single layer, is simple to manufacture, and provides excellent isolation characteristics.