Phase centre analysis of planar array antennas: Application to a microwave landing system

A mathematical model is developed to determine the antenna phase centre and its uniqueness. The model is then used to investigate the phase centre location for the azimuth antenna of a Microwave Landing System (MLS) and to determine its movement due to beam scanning and various design or operational errors. It is shown that, for an ideal antenna, i.e., the error-free case, the phase centre coincides with the antenna's geometrical centre. However, any deviation from ideal conditions, due to design, fabrication or operational errors, phase shifter quantization and the scan angle algorithm, causes its non-uniqueness and movement from the antenna's geometrical centre. The method is also used to treat environmental effects, such as ground reflection and thermal expansion or contraction, on the location of the antenna phase centre.