  RISs are an emerging technology for engineering the channels of future
wireless communication systems. The vast majority of research publications on
RIS are focussing on system-level optimization and are based on very simplistic
models ignoring basic physical laws. There are only a few publications with a
focus on physical modeling. Nevertheless, the widely employed model is still
inconsistent with basic physical laws. We will show that even with a very
simple abstract model based on isotropic radiators, ignoring any mismatch,
mutual coupling, and losses, each RIS element cannot be modeled to simply
reflect the incident signal by manipulating its phase only and letting the
amplitude unchanged. We will demonstrate the inconsistencies with the aid of
very simple toy examples, even with only one or two RIS elements. Based on
impedance parameters, the problems associated with scattering parameters can be
identified enabling a correct interpretation of the derived solutions.
