THE ARRAY DESIGN PROBLEMThe array design problem consists in determining the optimal locations for the antenna pads. Three main difficulties arise when trying to solve this problem:
The main constaints on the design are the number of pads, the topography, and the wiring cost and the access to the antennas. The scientific specifications depend on the purpose : imaging requires low sidelobes, and correct uv-sampling, astrometry requires high resolution i.e. long baselines and detection requires high sensitivity towards short baselines, i.e. compact configurations.the constraints and scientific specifications are numerous and sometimes incompatible; the technique of interferometry is complex and the translation of the scientific specifications and constraints in terms of specifications for the Fourier components (visibilities) to be measured is not straightforward; once defined, the specifications for the visibilities cannot be directly translated in terms of antenna positions. The derivation of the specifications in terms of distribution of Fourier samples is an essential issue. Several works (e.g Woody 2001, a & b ) were devoted to that question. I addressed the problem in Boone 2002 . The main results of the analysis developed in this paper are summarized in the next section .
In Boone 2001 I introduced an optimization method able to optimize antenna locations for any target distribution of visibilities. It is an efficient tool that allows to overcome the last difficulty of the list above, namely the derivation of the antenna locations for some specifications on the distribution of samples. A software based on this method is available and some documentation is given in the optimization software section.
The optimization method is being applied to the design of ALMA configurations using the target distributions as defined by the analysis presented in the next section ..The resulting configurations are presented in the ALMA configurations section.
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