Broadband Huygens' Metasurface Based on Hybrid Resonances
Recently, a special class of Huygens' surfaces has been proposed which are capable of manipulation of transmitted wavefronts while exhibiting high transparency over a broad range of frequencies. In this work we propose and study a new meta-atom for achieving broadband transparency of Huygens' surfaces based on two mutually shifted split-ring resonators. The resonators were carefully optimized using a new developed analytical model so that their electric and magnetic responses was balanced to achieve unidirectional scattering of the incident field. Moreover, their mutual shift canceled their inductive coupling so that both the responses were resonant at the same frequency and the meta-atom exhibited no magneto-electric coupling. The analytical prediction of broadband transparency along with the frequency-dependent phase shift of the transmitted wave within the full coverage of $360\degree$ has been verified numerically and experimentally in the microwave range. The proposed metasurface can be used for symmetric high-efficient polarization conversion and beam-splitting, and opens the way for other interesting applications.