On the Feasibility of a Generic Phased Array Feed for the European VLBI Network

The feasibility of using a generic Phased Array Feed (PAF) for the radio telescopes within the European VLBI Network (EVN) is explored. Taking into consideration the variations in size ($\mathrm{1 4} \mathrm{~ m}-100 \mathrm{~m}$) and primary focal distance to diameter ratios $f / D(0.3-0.5)$ of the EVN reflectors, the achievable aperture efficiency of a generic array feed is investigated. For the scan range of $0^{\circ}-5^{\circ}$, a parametric study based on encircled power is performed to find the optimum location, shape and size of the array. It is concluded that for a generic PAF design, the smallest $f / D$ ratio decides the required array size for a certain aperture efficiency and scan angle. A spherical array with specific radius of curvature and displacement from the focus is found to achieve $80 \%$ aperture efficiency with smaller size, both in terms of radius projected onto the focal plane and surface area, than a planar array placed in the focal plane.