MMA Memo #260

A Comparison of Zoom Arrays with Circular and Spiral Symmetry

J.E.Conway (Onsala Space Observatory, Sweden)

April 12, 1999

Keywords: Arrays, Configuration

There are advantages in making the intermediate arrays of the MMA/LSA which fill the 3km plain so-called 'zoom' arrays. In such arrays the antenna pads are arranged according to a scale-free self-similar distribution. By moving antennas from inner pads to outer ones the array gradually expands keeping a self-similar uv coverage. So far two types of zoom array have been proposed, one based on a definite shape, a three-armed logarithmic spiral (Conway 1998), and another assuming a circularly symmetric inverse-square law density of pads (Webster 1998). In this memo we make a first comparison of these two geometries. In the arrays tested we find small but significant advantages of the spiral geometry over the circularly symmetric ones; both in terms of uv coverage and how well the geometry stays self- similar as the array zooms. Although better untested circularly symmetric configurations may exist the advantages we see for the spiral appear to be intrinsic; coming fundamentally from its three- fold symmetry and the 'open' nature of this pattern. Despite these small differences we argue that both circular and spiral zoom arrays have better capabilities than the series of set array configurations that have dominated array configuration planning up to now.

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Last modified: 09 December, 1999