Advanced Calibration Method For Accurate Microwave Absorber Reflectivity Measurements At Oblique Illumination Angles

The increasing complexity of new radio systems re- quires a change of measurement sites towards more sophisticated virtual electromagnetic environments. RF absorbers are an essential element of these environments to achieve the propagation conditions desired by obtaining well-defined measurement conditions and suppressing interfering signals. Optimal propagation conditions can only be achieved by sufficient knowledge of the frequency-and angle-dependent reflectivity of RF absorbers. For this purpose, an advanced calibration procedure for reflectivity measurements at oblique illumination angles based on a combination of the established RCS- and NRL-arch methods is proposed. Measurement results obtained with the new technique show good consistency with the NRL-arch method in the specular case but with the advantage of accessing the angle-dependent behavior of the RF absorbers. Therefore, the proposed calibration procedure will not only help manufacturers to characterize their absorbers more effectively, but additional knowledge of the off-normal reflectivity will also contribute to the optimization of measurement sites such as virtual electromagnetic environments.