A. G. Willis

Demonstration of a Dual-Polarized Phased-Array Feed

We describe the design and construction of a dual-polarized phased-array feed (PAF) with the purpose of demonstrating this technology as a means of expanding the instantaneous field-of-view of radio telescopes. The PAF beamformer is calibrated with observations of an unpolarized astronomical radio source, the covariance matrix of all receiver channels is calculated, and the two dominant eigenvectors are then used as beamformer weights. We show measurements demonstrating the capabilities of this instrument as a polarimeter, and confirm that the calibration method does produce orthogonally-polarized beams. These results are then analyzed to show the sensitivity to fluctuations in gain and phase in the multiple parallel receiver chains making up the phased-array feed. We also compare the performance of PAFs that beamform all array elements with PAFs that beamform only co-polarized elements.

New spectral line multibeam correlator system for the James Clerk Maxwell Telescope

A new Auto-Correlation Spectral Imaging System (ACSIS) for the James Clerk Maxwell Telescope (JCMT) is being developed at the National Research Council of Canada, in collaboration with the Joint Astronomy Centre and the United Kingdom Astronomy Technology Centre. The system is capable of computing the integrated power-spectra over 1-GHz bandwidths for up to 32 receiver beams every 50 ms. An innovative, multiprocessor computer will produce calibrated, gridded, 3-D data cubes so that they can be viewed in real-time and are in hand when an observation is over. When connected to arrays of receivers at the Nasmyth focus of the telescope, the system will be able to rapidly make large-scale images with high spectral resolution and map multiple transitions. The ACSIS system will be mated initially with the multibeam 350-GHz receiver system. Heterodyne ARray Program (HARP), under development at the Mullard Radio Astronomy Observatory in Cambridge, England. In this paper we describe ACSIS, how it is designed and the results of key performance tests made.

A Real-Time Parallel-Processing Imaging System for Radio Astronomy

ACSIS (Auto Correlation Spectrometer Imaging System) is a real- time data collection and reduction system intended for use with a 16 pixel receiver at the James Clerk Maxwell Telescope on Mauna Kea, Hawaii. At peak operating speed, the correlator connected to each receiver will generate an autocorrelation lag array of 8192 numbers every 50 ms, or 10.5 Mbytes of data every second. The ACSIS reduction system converts raw lag-data into calibrated radio-frequency spectra as the data are obtained. In mapping modes, these spectra are further inserted into a 3-dimensional data cube of image planes as a function of radio frequency. The reduction system should produce calibrated data of sufficient quality that further o-line processing is not required.