Fast and Accurate Antenna Alignment Correction Performed using a Vector Isometric Rotation

The success of most traditional implementations of antenna measurement techniques whether near field, far field or compact, assume that a fiducial mechanical datum associated with the antenna under test (AUT) can be accurately and precisely aligned to the mechanical axes of the test range. Unfortunately, an alternative approach is sometimes necessary, as achieving such careful alignment is not always convenient or possible. Instead, if the relationship between the frame of reference associated with the antenna and the frame of reference associate with the range can be acquired, i.e. assuming that it is known, then in principal any misalignment can be corrected for within the data processing chain. Techniques for rigorously implementing the necessary vector isometric rotation are well documented and usually utilise the concepts of a modal expansion. In general this is not always convenient as these methods can be difficult to implement and often require the transformation of one modal expansion to another, e.g. planar or cylindrical to spherical, etc. This paper describes the additional post processing that is required to yield alignment corrected far field data from an acquisition of an imperfectly aligned antenna. A general-purpose vector isometric rotation strategy is utilised that is reliant upon interpolation, rather than a particular modal expansion. The interpolation is performed using a polar, i.e. amplitude and phase, implementation of a two dimensional bi-cubic convolution interpolation algorithm. The effectiveness of this technique is then demonstrated through the use of range measurements.