Wideband double-layer reflectarray antenna employing subwavelength multi-resonant elements for C-band application

This paper presents a wideband C-band reflectarray antenna based on subwavelength triple-resonant phase engineering to address the inherent bandwidth limitation of conventional single-resonant reflectarrays. The proposed unit cell, with a compact size of 0.33 λ ₀ (where λ ₀ is the free-space wavelength at the center frequency) at 6.2 GHz, employs a double-layer configuration composed of two PTFE substrates (relative permittivity ε r = 2.55) separated by a 3-mm air gap and printed with three metallic layers. By deliberately introducing three staggered resonances through arc delay-lines, Koch-fractal loops, and cross-shaped resonators, the reflection-phase dispersion is significantly flattened across 4.76–6.70 GHz. Unlike tightly coupled or three-dimensional reflectarrays that enhance bandwidth at the expense of structural complexity, the proposed design achieves broadband operation through systematic phase-slope control while maintaining a planar and fabrication-friendly architecture. An 11 × 11 prototype with a 200 mm × 200 mm aperture was fabricated and fed by a broadband log-periodic dipole antenna to ensure stable aperture illumination. Measured results demonstrate a 3-dB gain bandwidth of 19%, a peak gain of 19.9 dBi at 6.2 GHz, sidelobe levels below −12 dB, and cross-polarization below −29 dB across the operating band. The proposed approach provides an effective and compact solution for broadband C-band reflectarrays through phase-dispersion engineering rather than structural enlargement or complex feeding networks.