ISSTT Proceedings

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Ideal Grid Generates Cross Polarization

Authors:
B. Lazareff, S. Mahieu, D. Geoffroy
Abstract:
The ALMA Band 7 cartridge dual-polarization cold optics has been designed to meet a number of specifications, among which the level of cross polarization (initially <-20dB, now <-23dB). The initial design was based on the assumption that the coupling diagram from each of the two horns would be free from cross polarization (Xpol) just beyond the polarization diplexing grid, with the only contribution to Xpol comping from the final refocusing mirror. Initial measurements were showed levels of Xpol significantly worse than expected. This led (after some time) to the realization that an ideal grid can generate cross polarization, which can be brought down to a negligible level by a proper orientation of the grid. The design has been modified accordingly, and the measurements indeed have shown a significant improvement, that allowed a tighter specification to be instated.
Categories:
Quasi Optics, Waveguides
Year:
2009
Session:
P2
Full-text:
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Page Number(s):
223-226