FEIC Beam Scanning meeting -- 28 August 2008


  • Date/time: 28 Aug 2008 14:00 EDT = 18:00 UT
  • Attendees: Josh, Antonio, Geoff, Sri (NTC); Fred and Todd (CV), Darrel (TU), Richard (JAO)

Action Items from previous meeting

  • Geoff will make measurements with the Band 9 open waveguide feed and report on the results.
  • Josh will reanalyse the bands 6 and 7 PAI data, using the latest spreadsheet originating from Richard.
  • We need to sort out the discrepancy with Andrey's analysis. Antonio will talk to Andrey, and Josh and/or Todd will set up a simple wiki page so that Andrey's intermediate analyses and our own can be compared directly. We will then arrange a teleconference involving Andrey, Richard and other members or this group to home in on what Andrey is doing differently from ourselves. This should be done as soon as practical. Antonio will find out Andrey's availability to arrange a suitable time for this teleconference.
  • The discrepancy between NSI analysis of different probe polar diagrams: Todd and Fred will take suitable existing raw data sets for two different probes, and process them themselves - using our own probe pattern correction, and FFT. This will be compared to the NSI analysis. Is the problem with the NSI representation of the polar diagrams, with the NSI analysis, or what?


  • Josh contacted NSI. Here is what he learned:
    • Q. Are we able to view the raw nearfield data, completely unprocessed in any way?
    • A: Yes. If we do not use the nearfield preprocessing options, and don't use normalization.
    • Q: Position-phase correction. The manual states that for a scan which included two separate beams, "Position phase correction", if enabled, will apply a 90 degree phase shift to beam 2, so that an average beam listing may be produced. I have observed that enabling phase correction applies a phase shift to both beams 1 and 2, and this shift is not 90 degrees. The purpose of phase correction is to offset the phase difference introduced by the 1/4 wavelength difference in distance from horn to AUT. When examining overlayed Hcuts for beams 1 and 2, position-phase correction does not appear to appropriately offset the phase difference between the two beams.
    • A: He'll get back to me on that after investigating further on his end.
  • Richard sent a plot suggesting that Andrey's farfield plot and NSI's farfield plot (for one of the beams, not the average) are quite different. However, after the meeting, he found that there was a missing square root and the two are in better agreement. See this plot.
    • ACTION ITEM: Josh will send out the NSI farfield data for the average of beam 1 and beam 2. Richard will compare them with Andrey's result.
  • Fred said that his FFT of the nearfield data for scan 103 with the proper avg of beams 1 and 2 (with no padding) look essentially identical to Andrey's data.
    • ACTION ITEM: Fred will proceed with implementing efficiency calculations in Mathematica.
  • Todd described the wiki that he set up for the FEIC beam group (i.e. these pages).
  • No new band 9 measurements have been made. Geoff expects to get control of the receiver tomorrow morning.
    • ACTION ITEM: Geoff will make new band 9 scans using the open-ended waveguide probe.
  • We did not get to talk about bands 6 and 7 PAI data, presumably this analysis has not yet been done due to the talking with NSI and generating data files.

-- ToddHunter - 20 Aug 2008

Topic attachments
I Attachment Action Size Date Who Comment
Comp.pdfpdf Comp.pdf manage 27 K 2008-08-28 - 16:27 ToddHunter comparison of NSI farfield (one beam only) with Andrey's (avg of beam 1 and 2)
This topic: ALMA > WebHome > FrontEndIntegrationCenter > FEICBeamScanningResults > FEICBeamScanningMeeting2008aug28
Topic revision: 2008-08-28, ToddHunter
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