The rapid growth of 5G and next-generation wireless systems demands antenna solutions capable of supporting massive data rates, low latency, and reliable operation in dense communication environments. Millimeter-wave bands, in particular, require compact, wideband, and low-interference antenna architectures to ensure stable and efficient performance. This paper presents a compact wideband circularly polarized (CP) 2-element MIMO antenna specifically designed for millimeter-wave 5G applications. The antenna, implemented on an RT Duroid 5880 substrate ( \(\varepsilon _r = 2.2\) , thickness = 1.6 mm), achieves CP through a novel square-slot perturbation introduced in the radiating patch. To enhance isolation, a modified mushroom-shaped electromagnetic band gap (EBG) structure is incorporated, effectively suppressing surface waves and minimizing mutual coupling. This innovative EBG-assisted configuration results in an exceptionally low envelope correlation coefficient (ECC < 0.01) and a diversity gain close to 10 dB, demonstrating excellent spatial diversity. The proposed design offers a wide \(-10\) dB impedance bandwidth spanning 21-45 GHz (72.7%), a 3 dB axial-ratio bandwidth from 27-45 GHz, and a peak gain of 7.5 dB near 30 GHz. Strong agreement between simulated and measured results validates the antenna’s performance. With its compact profile, enhanced isolation, and wide CP bandwidth, the antenna serves as a novel and high-performance candidate for mmWave 5G applications including smart infrastructure, vehicular networks, and wireless backhaul systems.
