Hybrid arrays: design of reconfigurable aperture-synthesis interferometers

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 decided when the telescope is designed. The main consideration is 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. The appropriate taper can, however, depend on the astronomical source under study and on the particular reasons for making the observations, and no single layout can be ideal for all cases. In the paper hybrid arrays are considered in which some of the antennas are removed from one configuration and resited on existing stations of the next smaller configuration in order to change the taper. Telescopes are considered whose basic configurations are concentric rings consisting either of circles or of Reuleaux triangles. Some of the hybrid arrays generated in this way are found to have reasonable beam profiles, provided that 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 as the basis of hybrid arrays