Tarik El Arrouch, Sudipta Das, Namrata V. Langhnoja, Tanvir Islam, Abeer D. Algarni, Najiba El Amrani El Idrissi, Boddapati Taraka Phani Madhav
ABSTRACT In this article, ultra‐wideband (UWB) single‐element and two‐port multiple‐input‐multiple‐output (MIMO) antenna structures with circular polarization (CP) characteristics are designed to support numerous modern wireless systems. The basic CP element is designed to obtain an ultra‐wide operating bandwidth. In the design process, a circular stub is integrated into the ground plane, and a circular slot is structured into the patch to achieve CP. On the other hand, a rectangular stub is used to improve the axial ratio bandwidth (ARBW). The elemental antenna achieves an impedance bandwidth (IBW) of 97.96% (4.13–12.06 GHz), an ARBW of 49.62% (5–8.3 GHz), a peak gain of 5.75 dB, and a minimum efficiency of 80%, maintaining small dimensions of 20 mm 20 mm 1.6 mm (0.275 λ 0 × 0.275 λ 0 × 0.022 λ 0 ). Meanwhile, a two‐element UWB MIMO radiator of 20 mm 44 mm 1.6 mm (0.275 λ 0 × 0.606 λ 0 × 0.022 λ 0 ) is designed and experimentally validated. It addresses the challenges of achieving wide impedance and axial‐ratio bandwidths while maintaining a compact size and high isolation for MIMO operation with attractive diversity performance. It achieves an impressive ultrawide IBW of 100% (4–12 GHz), ARBW of 42.73% (4.6–7.1 GHz), and 10.90% (7.8–8.7 GHz) while offering improved isolation. The MIMO geometry exhibits outstanding diversity performance, with an envelope correlation coefficient (ECC) < 0.01, diversity gain (DG) > 9.92 dB, total active reflection coefficient (TARC) < 10 dB, and channel capacity loss (CCL) < 0.2 bits/s/Hz. These features render the proposed UWB MIMO antenna exceptionally appropriate for various wireless communication uses, such as microwave C‐band (4–8 GHz), WiMAX (5.725–5.850), WLAN (5.150–5.825 GHz; 5.925–7.125 GHz), and satellite communication in X‐band (downlink: 7.25–7.745 GHz and uplink: 7.9–8.4 GHz).