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We describe the design and construction of a dual-polarized phased-array feed (PAF) with the purpose of demonstrating this technology as a means of expanding the instantaneous field-of-view of radio telescopes. The PAF beamformer is calibrated with observations of an unpolarized astronomical radio source, the covariance matrix of all receiver channels is calculated, and the two dominant eigenvectors are then used as beamformer weights. We show measurements demonstrating the capabilities of this instrument as a polarimeter, and confirm that the calibration method does produce orthogonally-polarized beams. These results are then analyzed to show the sensitivity to fluctuations in gain and phase in the multiple parallel receiver chains making up the phased-array feed. We also compare the performance of PAFs that beamform all array elements with PAFs that beamform only co-polarized elements. [ABSTRACT FROM AUTHOR]

A novel approach for analysing the quasi-optical large adaptive reflector Cassegrain system is described. In this system a feed-reflector is used to illuminate a hyperboloid sub-reflector with 5-10m diameter, located 500m above the ground. In the proposed method of analysis the feed-reflector aperture field distribution is expanded into a set of Gaussian--Laguerre modes. These modes propagate from the feed-reflector aperture in a simple and well defined way. The feed-reflector near-field radiation pattern is calculated at the subreflector location. The subreflector parameters in this system are found by maximising the LAR aperture efficiency, which includes phase and taper efficiencies, and minimising the LAR spillover loss. This process is computationally more efficient than the physical-optics current-distribution method and more accurate than the ray-tracing approach. It also provides a new insight into the operation of the feed-reflector system. [ABSTRACT FROM AUTHOR]