Behaviour of orthogonal wave functions and the correction of antenna measurements taken in non-anechoic environments

The measurement and post-processing mode orthogonalisation and filtering technique, named Mathematical Absorber Reflection Suppression (MARS), has been used extensively to identify and subsequently extract measurement artefacts arising from spurious scattered fields that are admitted when antenna testing is performed in non-ideal anechoic environments. Underpinning the success of the MARS post-processing, and other mode orthogonalisation and filtering strategies, is the behaviour of the orthogonal vector wave (mode) expansions that are employed to describe the radiated fields and in particular their behaviour under the isometric coordinate translations that are central to the post processing. Within this paper, simulated and measured data will be used to illustrate the applicability of this measurement and post processing technique paying particular attention to the behaviour of the various modal expansions examining and confirming specific, commonly encountered, measurement conventions.