Printed circuit metasurfaces have attracted significant attention in the microwave community for their capability of versatile wavefront manipulation. Despite their promising potential in telecommunications and radar applications, few transmissive metasurfaces have been reported operating at millimeter-wave frequencies. Several secondary effects including fabrication tolerances, interlayer near-field coupling and the roughness of conductors are more severe at such high frequencies and can cause significant performance degradation. Additionally, experimental characterization techniques reported previously are not accurate enough for the verification of such effects. In this work, we present highly efficient refracting metasurfaces operating at 83 GHz. We use a sophisticated synthesis technique that minimizes possible effects of performance degradation such as interlayer near-field coupling and the influence of fabrication tolerances. Additionally, we propose a new experimental technique for the characterization of periodic metasurfaces. Using this technique, we present for the first time an accurate determination of the intensity of propagating Floquet harmonics in a broad frequency range. The proposed method gives deep insight into the beam refraction problem as it accurately quantifies in which direction energy is scattering. Additionally, it verifies our numerical model.