Experimental evaluation of polarimetric beamformers for an L-band phased array feed

A novel method to form multiple high-sensitivity beams with a reflector based radio telescope is to use a phased array feed (PAF). To accurately reconstruct the polarization state of the incident radio waves, the beam patterns of the PAF are of crucial importance. The co- and cross-polar element patterns of an oversampled L-band PAF prototype system have been measured in an interferometric setup. It is demonstrated that, although the antenna elements sampling the two orthogonal polarizations of the focal field are not co-located, dual polarized beams can be formed by combining the element responses in a beamformer. The capability of the PAF to optimize its beams in terms of sensitivity, sidelobes and polarization characteristics is demonstrated.