Editing Submillimeter Array (section)

== Antennas ==
[[File:SMAAntenna1.png|thumb|An SMA antenna deployed on a pad]]
Each of the eight antennas has a 6 meter diameter primary mirror made of 72 machined cast aluminum panels.   Machined aluminum was chosen over the lighter carbon fiber alternative, because of concerns that heavy snow accumulation, or windblown volcanic dust, might damage fragile carbon fiber panels.   The panels, each about 1 meter wide, were machined to an accuracy of 6 microns.   They are supported by a carbon fiber tube backup structure, which is enclosed by aluminum panels to protect it from windblown debris.   The positions of the panels can be adjusted from the front of the dish.

The initial adjustment of the surface panels in Hawaii was done in the service hangar, using a rotating template.   After the antennas were deployed, the surfaces were measured using near-field holography with a 232.4 GHz beacon source mounted on the exterior cat-walk of the Subaru building, 67 meters above the SMA's subcompact pad ring.   The panel positions were adjusted based on the holography results, and holography guided adjustments are repeated periodically, to maintain the surface quality.   After several rounds of adjustment, the surface's error is typically about 15 microns RMS.<ref>{{cite book |last1=Sridharan |first1=T.K. |last2=Saito |first2=Masao |last3=Patel |first3=Nimesh |title=Holographic Surface Quality Measurements of the Sub-Millimeter Array Antennas |date=August 2002 |publisher=URSI General Assembly |location=Maastricht |url=https://www.ursi.org/proceedings/procGA02/papers/p1387.pdf |access-date=11 November 2020}}</ref>

Heating units are installed on the primary mirror, the quadrupod supporting the secondary mirror, and the secondary mirror itself, in order to prevent ice formation in high humidity conditions.

Each antenna has a cabin holding the electronics needed to control the antenna, as well as the Nasmyth focus receivers.   This temperature-controlled cabin nearly encloses the antenna's steel mount to minimize pointing errors due to thermal changes.