ALMA Memo #291: First Simulations of Imaging Performance of a Spiral Zoom Array; Comparisons with a Single Ring Array

Imaging simulations have been carried out with a version of the spiral zoom array presented in Conway(2000) (Memo 283). Two test images were used, one based on a VLA image of Cygnus A and another based on an OVRO CO map of M51. Both snapshot and long track CLEAN simulations were carried out. The results were compared with those obtained for a single ring array with similar resolution. The single ring array has a fairly uniform coverage out to its maximum baseline and therefore provides a useful constrast to the spiral zoom array which has a strongly tapered (almost gaussian) coverage. For both test images the spiral array gave better imaging performance. The difference was particularly large for the case of the long-track observations when the rms errors were 10 times larger for the ring than for the spiral arrays. This large difference arises because the large near-in sidelobes of ring arrays, caused by the sharp edge to the uv-coverage, persists even after a long track.