Paving the Way for Suitable Metasurfaces’ Measurements Under Oblique Incidence: Mono-/Bistatic and Near-/Far-Field Concerns

This paper aims at contributing to the specialized literature on the experimental characterization of metasurfaces (MTSs) reflectivity. The growing demand for angularly stable MTSs reinforces the relevance of the results under oblique incidence. Generally, reflection coefficient phase measurements are more challenging than the amplitude ones. Thus, an artificial magnetic conductor (AMC) is used to analyze the critical aspects for enlarging the angular margin that can be properly measured. The importance of the retrieving methodology along with the proposed data postprocessing is highlighted among the involved issues, according to the obtained results. The suitability of monostatic versus bistatic measurement setups for comparison with plane-wave simulation is studied. The aforementioned AMC is experimentally characterized using both setups providing relevant conclusions. The tradeoff between the manufactured prototype dimensions (to resemble the simulated infinite one) versus the required anechoic chamber size (to fulfill far-field (FF) conditions, i.e., the plane-wave incidence for the considered frequencies) is tackled. Indeed, a thorough literature revision shows that most authors do not have this key aspect into account. The relevance of the resulting error from comparisons between the near-field (NF) retrieved measurements versus plane-wave simulation results is unveiled. This is even more critical when the angular stability is analyzed, since the scattering patterns of the AMC are not conformed at NF distances, which makes the errors even greater. Consequently, noteworthy conclusions concerning the characterization of AMCs in particular and MTSs in general regarding FF or NF measurements and angular stability analysis will be presented.