ALMA Memo #355
Design of the ALMA's Compact Configuration with the Road Design First.

L. Kogan

At the recent PDR of the ALMA configurations (Grenoble, February 26-27, 2001) the committee selected the best brightness sensitivity as a main criterion of the compact configuration design. The best brightness sensitivity is equivalent to the most wide synthesized beam or the smallest size of the array configuration. The self shadowing of antennas requires some minimum spacing between antennas. During reconfiguration each antenna has to be accessible by the transporter. And this make even more requirement to the spacing between antennas. So it looks like that the problem of achievement of the best brightness sensitivity is equivalent to the problem of minimizing area of the road inside of the array. The previous designs of the compact configuration were leaving the road problem to the end. At the same time the road requirement can destroy the original good configuration. That is why I suggest to design the road with minimum area at the beginning and then design the configuration itself considering the roads as a topography constrain. Such an approach can be considered as a complete design because the road area is minimized since the beginning and therefore the brightness sensitivity is maximized. Optimization of the side lobes can be carried out by the standard procedure at AIPS (task CONFI) using the road constrain as a topography constrain. The road file has to be created at the standard Butler's format used for the site topography.

At this memo I give several examples of the roads and relevant configurations. The synthesized beam widths are compared with ideal hexagon configuration beam.

One of the configurations has the beam width very close to the ideal hexagon configuration of the given spacing.

View a pdf version of ALMA Memo 355.