Full-phase single-layer metasurfaces with C4-symmetric resonators via multipolar interference

Complete and efficient manipulation of electromagnetic (EM) waves is a cornerstone for creating advanced functional devices. However, conventional single-layer passive metasurfaces often face an intrinsic trade-off between phase-modulation range and reflection efficiency. To overcome this limitation, we propose and demonstrate a design paradigm that achieves full 360° phase coverage with near-perfect reflectivity by intentionally engineering the unit cell's symmetry. Specifically, by reducing the symmetry from C4v to C4, we introduce a magnetic dipole resonance that hybridizes with the original electric dipole mode. This dual-resonance interference closes the phase gap and circumvents amplitude nulls, while the preserved C4 rotational symmetry guarantees a robust polarization-insensitive response. By systematically varying the geometry at 10 GHz, these multipolar modes are synergistically tuned for continuous phase control. To validate this concept, a library of 36 unit cells was established to demonstrate two functional metasurfaces for electromagnetic focusing and holographic imaging. This work provides a robust and elegant paradigm for developing single-layer passive metasurfaces with superior performance, promising wide applications in high-performance microwave imaging, next-generation wireless communications, and advanced radar systems.