Circularly polarized millimeter-wave hemisphere DRA employing FSS polarizer and dielectric superstrate for 5G applications

This paper presents a compact, wideband, high-gain circularly polarized (CP) hemispherical dielectric resonator antenna (HDRA) designed for millimeter-wave 5G applications. The proposed antenna employs a linearly polarized (LP) HDRA excited through an annular slot coupled to a 50-Ω microstrip feed, enabling efficient radiation at millimeter-wave frequencies. Wide impedance bandwidth from 20 to 28 GHz is achieved by overlapping multiple adjacent resonant modes of the HDRA. Circular polarization is realized by introducing a frequency-selective surface (FSS) superstrate positioned at an optimized distance above the antenna. To further enhance the axial-ratio bandwidth and gain, a 2 × 2 HDRA array with a sequential-phase feeding network and an additional dielectric superstrate is implemented. The antenna is fabricated and experimentally validated. Measured results demonstrate an impedance bandwidth of 33.3% (20-28 GHz), a peak realized gain of 11.8 dBi, and a 3-dB axial-ratio bandwidth of 31% (20.5-28 GHz). The proposed design offers a compact and efficient solution for millimeter-wave 5G and IoT applications.