Compact Dual-Resonance Element With Low Phase Sensitivity for Offset Reflectarray Antennas

Generally, conventional elements of planer reflectarray antennas (RAs) suffer from incomplete phase variation range (less than 360 degrees), high phase sensitivity, or large size. Here, we propose an isotropic three-turn square-ring resonator element on a single-layer substrate working at X-band. The element is not only electrically small and dual resonant to cover a complete reflection phase-shift range of (0 degrees, 360 degrees), but also achieves a flat slope of the phase curve due to the fourfold rotational symmetry, and both aspects are essential to improve the radiation performances of the RAs. For potential applications, an offset RA has been optimized, fabricated, and measured. Numerical and experimental results coincide well, indicating that the sample advances in many aspects such as high aperture efficiency of better than 70%, 1-dB gain bandwidth of wider than 13%, and also competitive radiation gain. The proposed strategy opens an avenue to new types of high-efficiency metasurfaces and RAs with enhanced radiation characteristics.