  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.
