  A simple method of superimposing multiple near field scans using a single
horn antenna in different configurations to characterize a planar
electromagnetic metasurface is proposed and numerically demonstrated. It can be
used to construct incident fields for which the metasurface is originally
designed for, which may otherwise be difficult or not possible to achieve in
practice. While this method involves additional effort by requiring multiple
scans, it also provides flexibility for the incident field to be generated,
simply by changing the objective of a numerical optimization which is used to
find the required horn configurations for the different experiments. The
proposed method is applicable to all linear time-invariant metasurfaces
including space-time modulated structures.
