Paving the way for suitable metasurfaces’ measurements under oblique incidence: Mono/Bi-static and Near/Far Field concerns

Abstract

This paper aims at contributing to the specialized literature on experimental characterization of metasurfaces reflectivity. Growing demand on angularly stable metasurfaces 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 post-processing is highlighted among the involved issues, according to the obtained results. The suitability of monostatic vs bi-static measurement set-ups for comparison with plane-wave simulation is studied. The aforementioned AMC is experimentally characterized using both set-ups providing relevant conclusions. The trade-off between the manufactured prototype dimensions (to resemble the simulated infinite one) vs the required anechoic chamber size (to fulfil far-field (FF) conditions i.e. 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 near-field (NF) retrieved measurements vs plane-wave simulation results is unveiled. This is even more critical when the angular stability is analysed, since the scattering patterns of the AMC are not conformed at near-field distances, which makes the errors even greater. Consequently, noteworthy conclusions concerning the characterization of AMCs in particular and metasurfaces in general, regarding far-field or near-field measurements and angular stability analysis will be presented.