The effects of some mechanical uncertainties on the performance of welded and machined phased array antennas

Cost-effective manufacturing possibilities and inherent mechanical strength suggest the use of sheet metal constructions in large-size phased array antennas up to 3 GHz and above, applied both for civilian and military communication and radar systems. Constructional defects cause phase and amplitude errors which impair the radiation pattern by introducing non-symmetrical lobes and by filling wanted minima possibly up to -10 dB or creating phantom ones. Random phase deviations up to 60 degrees have been measured and gain variations of 2-3 dB are not rare. Typical faults include bends in the sheet structure due to welding and improperly aligned transmission line junctions in internal machined modules. A mathematical real-time compensation of most of these errors is feasible although in some cases this does not cure the actual fault but just masks the problem