Development of the ALMA Antennas
Development of the ALMA Antennas
In the Beginning
In 1992, the ALMA project (then called the MMA project) began looking at antenna designs which would allow fast position switching to achieve phase stable observations a large fraction of the time. Work began on a "slant-axis" antenna design (ie, ALMA Memos 94, 97, 98, 101, 105, 106). The stiffness of this design allowed very fast switching.
The slant-axis design evolved into an off axis parabaloid. The advantages of this off axis, slant-axis design included good gravitational performance, lack of counterweights, and the high sensitivity of an unblocked aperture.
A minimum blockage conventional antenna design, patterned after the BIMA 6 meter antennas, was prompted to provide a cost and performance comparison for the off axis, slant-axis design. In a side by side comparison, the off axis design was eliminated from consideration due to its poor field-of-view and polarization performance. Correction for the field-of-view and polarization was possible, but at the expense of the off axis design's sensitivity advantages.
Competing Prototype Antenna Engineering Design Concepts
In 1998, the formation of ALMA as an international partnership, brought together two different organizations, both with their own antenna design concepts. It was decided that the best way to determine the best design would be for that each organization to produce a prototype antenna for testing. The performance specifications for the antennas are rigorous, and the prototype antenna with the highest functionality will be the design used for the final construction of all 64 telescopes.
In 2001, Japan's entry into the international effort, brought a third antenna design for testing. The three prototypes are scheduled to be tested in 2002-2003, at the Very Large Array site in Socorro, New Mexico.
Additional documents related to the development of the antennas can be found in the ALMA Memo Series.