Recommendations: Polarization

1.

The polarization receiver specifications proposed by Larry D'Addario as stated in the Wolfgang Wild memo would appear to be satisfactory so long as other recommendations below are followed. These specs were that either linear or circular orthogonal polarization states are acceptable, with a maximum degree of non-orthogonality and of mismatch between antennas of -20 dB. Because linear receptors appear to be capable of delivering lower system temperatures, linear polarization would be preferred.

2.

The proposed special provision for circular polarization capability for band 7 would not be needed, as long as other recommendations are followed.

3.

We continue to recommend that band 7 be optimized for polarization work. This means that the design goal should be as clean as possible a polarized beam pattern. One aspect of this recommendation is a design goal of zero beam squint. Although a beam squint (and other polarized beam anomalies) of 3% could be addressed in principle by calibration, it will reduce polarization accuracy and sensitivity. In particular, these effects will be extremely important for single-dish polarization mapping, which will be essential for much of the polarization science that will be done.

4.

The Emerson bandpass calibration signal, stable in intensity and phase, should be included in the receiver design.

5.

The antennas must be designed and constructed for maximum stability of the polarized beam patterns. Without this, polarization mapping will be difficult if not impossible.

6.

Provision for testing the polarization characteristics of the two-antenna test array should be made. This will give the opportunity to test the system hardware and software for interferometer and single-dish polarimetry and identify problems before additional contracts are signed.