  In this paper, a proof-of-concept study of a $1$-bit wideband reconfigurable
intelligent surface (RIS) comprising planar tightly coupled dipoles (PTCD) is
presented. The developed RIS operates at subTHz frequencies and a $3$-dB gain
bandwidth of $27.4\%$ with the center frequency at $102$ GHz is shown to be
obtainable via full-wave electromagnetic simulations. The binary phase shift
offered by each RIS unit element is enabled by changing the polarization of the
reflected wave by $180^\circ$. The proposed PTCD-based RIS has a planar
configuration with one dielectric layer bonded to a ground plane, and hence, it
can be fabricated by using cost-effective printed circuit board (PCB)
technology. We analytically calculate the response of the entire designed RIS
and showcase that a good agreement between that result and equivalent full-wave
simulations is obtained. To efficiently compute the $1$-bit RIS response for
different pointing directions, thus, designing a directive beam codebook, we
devise a fast approximate beamforming optimization approach, which is compared
with time-consuming full-wave simulations. Finally, to prove our concept, we
present several passive prototypes with frozen beams for the proposed $1$-bit
wideband RIS.
