Adrian Webster [1]
June 4, 1998
Keywords:
Modern aperture-synthesis array telescopes usually have several configurations differing in size in order to provide the observer with a selection of compromises between angular resolving power and sensitivity. The layout of each configuration, however, is a choice for the designer of the telescope, the main consideration being the desired taper in the uv-plane coverage, which determines such properties as the sidelobe level, the width of the synthesised beam and the relative sensitivity to compact and extended components of the source. There is, unfortunately, no simple way of making this latter choice because it can depend on the source under study and on the particular reasons for making the observations. Implementing two or more types of configuration at each size would solve the problem but the cost of additional antenna stations usually rules this out, while weighting the baselines to change the taper in software reduces the sensitivity. It is therefore investigated to what extent an array may be converted from one type to another by removing some of the dishes from one configuration and resiting them on existing stations of the next smaller configuration to yield a hybrid array. Telescopes are considered whose basic configurations are concentric rings consisting either of circles or of Reuleaux triangles, both of which have a low ratio of the numbers of short baselines to long; moving some of the dishes to a smaller configuration then increases the ratio by providing additional short and medium baselines. Some of the hybrid arrays generated in this way are found to have reasonable radial profiles in the uv-plane providing the multiplicative scale factor between successive configurations is not too large, no more than about 3 or 4. Reuleaux triangles are found to be superior to circles for hybrid arrays not only because their radial profiles are smoother at all values of the scale factor but also because their desirable properties degrade more slowly as the scale factor is increased.
[1] ROE
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