Validation of the sample rotation scheme in the measurement of random-incidence scattering coefficients

The reverberation room method for measuring random-incidence scattering coefficients, standardized by ISO 17497-1, employs a sample rotation scheme to extract specularly reflected energy, where synchronized averaging of room impulse responses is performed during stepwise or continuous rotation of a test sample. However, the requirements of the stepwise and the continuous approaches are not yet clarified, particularly the latter employing the correlation technique with periodic pseudo-random signals. This paper theoretically elucidates the principles of the two approaches and formulates the error in scattering coefficient measured by each approach. Theoretical analyses demonstrate the minimum number of angular steps and the minimum revolution period that depend on the sample's scattering coefficient and the room's absorption area. Small- and full-scale experiments on the continuous approach verify that the minimum revolution period exists in the use of maximum-length sequence signals, however, the minimum number of signals exists in the use of swept sine signals, corresponding to angular steps in the stepwise approach.