FEIC Beam Scanning meeting -- 04 September 2008


  • Date/time: 04 Sep 2008 14:00 EDT = 18:00 UT
  • Attendees: Richard, Darrel, Fred, Todd, Josh, Geoff, Antonio

Action Items from previous meeting

  1. Josh will send out the NSI farfield data for the average of beam 1 and beam 2. Richard and Fred will compare them with Andrey's farfield result (which was a direct Fourier transform of the beam-combined raw nearfield data)
    • Richard's results: amplitude plot, efficiencies, explanation
    • 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.
  2. Fred will proceed with implementing efficiency calculations in Mathematica.
  3. Geoff will make new band 9 scans using the open-ended waveguide probe.

Recommendations from Richard made during the past week

  1. Read the NSI manual and do a third independent FT of the scan 103 data
  2. Make future maps with 127 x 127 points and a window size of 100.8126mm (so that the step matches the 12.7 micron stepper motor stepsize)


  1. Josh: We got a response from NSI regarding beam averaging in their software. In most of our previous beam scans, beam 2 was +90 deg from beam 1, which is opposite of what NSI assumes in its processing. But even using scans with the correct beam order, the result does not look right--seeing an extra 20 degrees. Josh will follow up with NSI.
  2. Fred is seeing good (but not perfect) agreement with Andrey's result if he does not correct for the half-pixel shift that should be applied due to having an even number of rows.
  3. Geoff reported some hardware problems with the beam scanning IF system. He is just getting the receiver again today and will proceed with scans with an odd number of rows, and with/without the open-ended waveguide.
  4. The new ALMA optics mailing list is available here: http://lists.alma.cl/mailman/listinfo/alma_optics

Action Items

  • Fred will continue his work with FFTs, half-pixel shifts and the like.
  • Richard will respond to Bernard on the recommended analysis procedure.
  • Geoff & Josh will continue with the planned Band 9, then Band 3, measurements, including measurements with open ended waveguide feeds.
  • We'll all think about the right way of dealing with the lambda/4 shifted measurement plane and how to cancel reflections: followup email thread

-- ToddHunter - 28 Aug 2008
Topic revision: r4 - 2008-09-13, ToddHunter
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