A Practical Approach to Locate Offset Reflector Focal Point and Antenna Misalignment Using Vectorial Representation of Far-Field Radiation Patterns

A direct and unambiguous approach to determine the focal point of a single offset reflector is presented. The proposed approach makes use of the vectorial form of far-field radiation patterns, both amplitude and phase. The method is based on iteratively defocusing the primary feed laterally and axially. First, mathematical expressions of the offset reflector with a small lateral and axial defocused feed are reviewed. Then, the numerical results are presented. It is shown how the corresponding far-field phase pattern information can be utilized to optimally locate the focal point of an offset parabolic reflector. The method can also be used to place the phase center of an unknown feed on the reflector focal point, and align the reflector on a test tower.