[asac][almanews] ALMA Memos 429 and 430 Released

[Stacy Oliver]

ALMA MEMO #429

Fixed-tuned waveguide 0.6 THz SIS Mixer with Wide band IF

A. Baryshev (SRON/NOVA), E. Lauria (NRAO), R. Hesper (SRON/NOVA), T. Zijlstra (DIMES), W. Wild (SRON)

2002/07/28

Keywords: SIS mixer, isolator, ALMA band 9, IF amplifier, noise temperature, waveguide mixer, fixed tuned, DSB mixer.

The Atacama Large Millimeter Array (ALMA) requires low noise SIS receivers for frequencies from about 80 GHz to 950 GHz with a very
large IF bandwidth (8 GHz SSB upper or lower sideband, 8 GHz DSB or 4 GHz dual sideband, upper and lower sideband). Since there will
be a large number of antennas in the array (currently 64), additional requirements such as high reliability, low cost, and the
production of a relatively large number of mixers have to be addressed. In this paper we report the results of a waveguide mixer
with a fixed backshort for ALMA band 9 (602 – 720 GHz). The mixer is based on standard Nb/AlOx/Nb SIS junction technology. This
mixer was tested with a wide band IF amplifier with and without isolator. Mixer measurement results for different LO frequencies
across a wide IF band (4-8 GHz) will be presented. DSB Receiver noise across the both RF and IF band was measured, and receiver
noise as low as 136 K at 650 GHz was demonstrated over the wideband IF. Finally, the possibility of a small production series of
such a mixer is discussed with results on a first batch of mixer-blocks will be presented.

View a pdf version of ALMA Memo #429.
http://alma.aoc.nrao.edu/memos/html-memos/alma429/memo429.pdf

Download a postscript version of ALMA Memo #429.
http://alma.aoc.nrao.edu/memos/html-memos/alma429/memo429.ps

________________________________________________________________________________________________

ALMA MEMO #430

Compact Configuration Evaluation - Mosaicing

Melvyn Wright Radio, Astronomy laboratory, University of California, Berkeley

2002/07/22

Keywords: Antenna Configurations, Image Simulations, Mosaicing

In this memo, we compare the mosaicing performance of compact configurations. MIRIAD scripts simulate mosaic observations with ALMA,
calculate error images and pipeline the results into tables. The residual imaging errors are characterized by the recovered flux,
peak flux density and the sidelobe levels. We present tables of the sidelobe levels and image fidelity for source declinations from
+60 to -60 degrees. Mosaic images for source diameters 24 and 32 arcsec are analyzed. For the 24'' source, a Gaussian configuration
provides the best image fidelity. For the 32'' source, the most compact configuration provides better sampling of the large scale
structure and better image fidelity, except at high declinations where the array is strongly shadowed.

View a pdf version of ALMA Memo #430.
http://alma.aoc.nrao.edu/memos/html-memos/alma430/memo430.pdf

Download a postscript version of ALMA Memo #430.
http://alma.aoc.nrao.edu/memos/html-memos/alma430/memo430.ps


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