[asac] [almanews] ALMA Memo 398 and 399 Released

[Stacy Oliver]

ALMA Memo #398

Impact of ACA on the Wide-Field Imaging Capabilities of ALMA

J. Pety, F. Gueth and S. Guilloteau (IRAM)

2001-11-18

Keywords: mosaicing, wide field imaging, ALMA simulator

This document presents the imaging simulations performed at IRAM to study
the importance of the ALMA Compact Array (ACA) on the wide field imaging
performances of ALMA. The simulations are based on a fast, approximate but
sufficiently accurate method. The image reconstruction is based on two new
CLEAN-based deconvolution methods for mosaics. The effects of i) pointing
errors, ii) amplitude calibration errors and iii) atmospheric phase noise
have been systematically studied. The effect of a poor knowledge of the
primary beams has also been studied. Finally we investigated the impact of
variations of the deconvolution parameters. A large number of simulations
have been performed, using several test images. This allowed us to
disentangle artifacts due to particular random sampling of the errors from
the genuine, average impact of these errors on all images. We find that
adding ACA observations improves the image quality of ALMA in some types of
images. More importantly, ACA provides robust results, when ALMA fails in
presence of some type of errors, or on some images. One of the two new
deconvolution techniques requires only a very moderate increase in computing
time to include the ACA data.

View a pdf version of ALMA Memo 398.
	http://www.alma.nrao.edu/memos/html-memos/alma398/memo398.pdf

Download a zipped ps version of ALMA Memo 398.
	http://www.alma.nrao.edu/memos/html-memos/alma398/memo398.zip



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ALMA Memo #399

Millimeter Wave Generation Using a Uni-Traveling-Carrier Photodiode

T. Noguchi, A. Ueda, H.Iwashita, S. Takano, Y. Sekimoto, M. Ishiguro, T.
Ishibashi, H. Ito, and T. Nagatsuma

2001-11-19

Keywords : photomixer, photodiode, millimeter-wave generation

We have designed a new photomixer using a uni-traveling carrier photodiode
(UTC-PD) for generation of W-band radiation. The UTC-PD is integrated on a
InP chip with DC and RF circuits and the chip is mounted upside down on a
fused quartz substrate which is placed in a microstrip channel across a
quarter-height W-band waveguide. A simple cross-shaped microstrip-waveguide
transition printed on the quartz substrate is used to couple power into the
waveguide. From the simulation it is found that this microstrip-waveguide
transition can give better than -15 dB return loss over 75--120 GHz. The
UTC-PD is irradiated by combined two lasers from the back side of the InP
chip. We have successfully produced difference-frequency radiation at 100
GHz with a power level of 1 mW by the photomixer.

View a pdf version of ALMA Memo 399.
	http://www.alma.nrao.edu/memos/html-memos/alma399/memo399.pdf

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