[mmaimcal] Change Request No 260: Relaxation of the Band 3 polarization efficiency specification

[Al Wootten]

Folks,

Although no comment from Science is on the reviewer or approval list for 
this change it does affect B3 science.  Comments appreciated by the 
ridiculously short and impending deadline of 9/30; they may be made on 
edm at:

http://edm.alma.cl/forums/alma/dispatch.cgi/changereq/docProfile/101873

260.  	Relaxation of the Band 3 polarization efficiency specification

CRE Number :
ALMA-40.02.03.00-0662-A-CRE


Description :
Relaxation is sought to the FE Requirement [FEND-40.00.00.00-00226-00 / 
AT] which requires that the polarization efficiency of the tertiary 
optics system shall exceed 99.5% for all ten bands. The proposed relaxed 
requirement (for Band 3 only) is 98% (-17 dB cross polarization in the 
integrated sense.) The peak cross polarization for the cold cartridge 
alone (without warm optics), [FEND-40.02.03.00-00298-00 / T], is sought 
to be relaxed to -19 dB instead of the presently specified -23 dB.

This request is instigated due to two factors: (i) several FE assemblies 
have been measured at the integration centers at this level of cross 
polarization for Band 3, and this represents the limit of 
achievable/measureable performance. (ii) The Band 3 cartridge group is 
unable to meet their originally specified cross polarization requirement 
(for the “cold cartridge alone”, without warm optics), due to 
manufacturability/yield concerns.

Note that, the cross polarization requirements for the Band 3 "cold 
cartridge alone" (without warm optics) are specified in terms of peak 
cross polarization performance (and not in the integrated cross 
polarization performance sense that the completed FE assembly is 
eventually evaluated against). This metric was chosen (somewhat 
arbitrarily) and meeting or failing this criteria at -23 dB peak cross 
polarization level does not guarantee compliance to the formal FE 
specifications one way or the other. This metric was chosen because 
integrating over the entire beam scan area (again without the warm 
optics) was thought to under estimate the cross polarization efficiency.

Statistics collected for the Band 3 cartridges produced thus far 
indicate that about 50% of the cartridges have a cross polarization 
performance (in the peak sense, on at least one polarization/test 
frequency combination) that is poorer that -23 dB with respect to the 
peak of the co-polarization pattern.

http://edm.alma.cl/forums/alma/dispatch.cgi/iptfedocs/showFolder/118271/def/def/3719192

CRE Form :
Upload the CRE form:
ALMA-40.02.03.00-0662-A-CRE.pdf

No Zon presence 	Eduardo Pizarro
	Posted on 2010-09-21 12:35
Modified by Eduardo Pizarro on 2010-09-24 06:33
Workflow state changed by Javier Marti on 2010-09-24 07:48
Author:
ksaini

Impact:
Date decision required:
2010-09-30 12:00

Name of supervisor who authorized the submittal of this change request:
Javier Marti (jmarti)

Reviewer List:
   	No Zon presence Kamaljeet S Saini (ksaini)
   	No Zon presence Pavel Yagoubov (pyagoubo)
   	No Zon presence Ravinder Bhatia (rbhatia)
Reviewer List Email Reminder (Days):
   	3
Approval List:
   	No Zon presence Dorsey L. Thacker (sthacker)
   	No Zon presence Gie Han Tan (ghtan)
   	No Zon presence Javier Marti (jmarti)
   	No Zon presence Dick Kurz (dkurz)
Approval List Email Reminder (Days):

Clear skies,
Al