Compact Quad-Port MIMO Antenna Employing Defected Substrate and Ground Plane for Sub-6 GHz 5G Communication

This work presents a low-profile, compact quad-port MIMO antenna structure optimized for sub-6 GHz and X-band wireless communication. The antenna employs a tapered and stepped monopole radiator in conjunction with defected substrate and ground plane modifications to enhance isolation, improve diversity performance, and support dual-band operation. A single monopole element, designed on an FR-4 substrate (ε<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> = 4.3, tan δ = 0.002), has been extended into a quadport configuration with orthogonally oriented ports to achieve polarization diversity and minimize mutual coupling. Although the spacing is less than λ<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub>/2 (0.14 λ₀), a reduced inter-element gap of 11.25 mm is adopted to achieve compact integration. The antenna measures 44 × 44 × 1.6 mm³ and operates across two frequency bands: 2.75–4.4 GHz and 10.33–13 GHz (S<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">xx</sub> < -10 dB) with S<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">xy</sub> values below –17.5 dB and –25 dB in the respective bands, ensuring robust MIMO performance. With its compact design and efficient radiation characteristics, the proposed antenna is well-suited for 5G-NR systems, IoT devices, V2X communication, and satellite-based applications.