Phase centre analysis of array antennas and its significance for microwave landing system

A mathematical model is developed that enables the determination of the array phase centre from its far field pattern. Its accuracy is established by investigating and locating the phase centre of selected small arrays. The method is then applied to typical microwave landing systems (MLS) phase arrays, specifically the azimuth antennas. Initially, various sources of errors are identified, that include errors due to the scan algorithm, phase shifter quantization and RMS errors, design and implementation errors, element and phase shifter failures, amplitude taper and quantization error, and the array element mutual coupling. A comprehension study is then carried out to compute the coordinates of the array phase centre and their variation due to each error. The results indicate that the phase centre location is not unique and depends strongly on the array tolerances and the types and magnitude of the errors. The results are also used to evaluate the antenna performance and to determine the effect of phase centre movement on the pointing angle, beamwidth and the side lobe levels