Radio-interferometric imaging of very large objects: implications for array design

High-quality images of fields larger than the field-of-view of the elements of an array of radio telescopes can be obtained from a mosaic of overlapping pointings. The addition of »single-dish« observations made with a telescope of the same size as the array elements suffices to produce images in which all Fourier components from the zero spatial frequency up to the maximum allowed by the array are properly represented. Image quality is then limited by systematic errors. Images with dynamic range exceeding 1000: 1 and a fidelity index of about 20 require antennas with rms surface accuracy of ∼λ/40 and pointing accuracy of ∼6% of the half-power beamwidth