Antenna phase center determination from amplitude measurements using a focusing lens

One critical performance parameter associated with feed systems for reflectors or other focused antennas is the feed phase center position. Maximum aperture efficiency is obtained when the feed phase center is positioned at the reflector focal point. Although horn antennas are the most common feeds for reflectors, lens antennas with bolometer detectors integrated at its base are the most common configuration [1] at millimeter and, especially, at sub-millimeter waves imaging and radiometric applications. Unlike horns, where the phase center position is normally located close to the aperture plane, the phase center of integrated lenses is very dependent upon the lens shape and may even be far out from the lens body. However, when bolometers or other detectors are used at the lens under test, only amplitude measurements can be obtained, preventing the usual phase center calculation from radiation pattern phase information. In this communication an alternative procedure based on power measurements is proposed and evaluated. Corresponding results obtained for a double-shell dielectric lens are compared to those obtained for the same lens with the usual method based on measured phase pattern. The alternative method uses an auxiliary collimated lens and can be used in small anechoic chambers.