Ultra-wideband CP Metasurface-Loaded Ring Antenna with Asymmetric Slots and EBG for 5g/satellite Applications

This paper presents a novel dual-resonance ultra-wideband (UWB) circularly polarized (CP) metasurface-loaded ring antenna, exhibiting |S11|<−10 dB over 2.1–2.78 GHz and 3.9–10 GHz (combined FBW ≈130%, compliant with FCC Part 15.517 UWB definition), with asymmetric slot perturbation and an electromagnetic bandgap (EBG) ground for enhanced gain in 5G and satellite communication systems. The antenna is fabricated on an RT/duroid 5880 substrate with relative permittivity ɛr=2.2, loss tangent tanδ=0.0009, thickness h=1.6mm, and overall dimensions of 40×40mm2. A 5 × 5 frequency selective surface (FSS)/metasurface grid is employed to improve impedance matching and radiation characteristics. The axial ratio (AR) remains below 3 dB over two distinct circular polarization (CP) bands, 3.5–4.8 GHz and 6.4–8.3 GHz, providing stable dual-band RHCP operation. Outside these frequency ranges, the AR increases beyond 3 dB and the polarization gradually transitions toward elliptical and linear states; hence, the CP behavior is explicitly characterized as dual-band rather than ultra-wideband. In this context, the term UWB refers to the impedance bandwidth, where |S11|<−10 dB is achieved over 2.1–2.78 GHz and 3.9–10 GHz, resulting in a combined fractional bandwidth of approximately 130%, consistent with FCC Part 15.517. With the inclusion of the EBG ground plane, the antenna achieves a peak realized gain of 12.5 dBi. The asymmetric slot perturbations of 0.8 mm and 0.6 mm effectively excite orthogonal resonant modes, thereby enhancing circular polarization purity within the two AR bands. Furthermore, the metasurface layer suppresses surface-wave propagation, resulting in an average front-to-back ratio (FBR) exceeding 25 dB and a peak FBR of approximately 30 dB at 8 GHz, while maintaining radiation efficiency greater than 85%. The broadside radiation patterns exhibit cross-polarization levels below −20 dB across the useful impedance bandwidth. Owing to its compact configuration and favorable bandwidth–gain trade-off, the proposed antenna outperforms conventional CP ring antennas and is well suited for sub-6 GHz 5G systems, low-Earth-orbit (LEO) satellite communication links, and radar applications.