Elimination of rotation axes offset error in antenna radiation pattern measurements using spherical wave expansion

The error caused by the offset between θ- and ϕ-rotation axes is eliminated from a measured antenna radiation pattern. Proper offset is found by minimising the difference between the original data field and the field of the spherical wave expansion (SWE) calculated from the data. Errors of the original and the corrected fields are estimated as the difference from a field calculated by the IE3D simulator for the antenna. The method is verified by comparing the obtained offset with a value given by minimising the phase difference between the measured and the simulated electric fields.