ALMA-FEIC Study Group. 2008-05-28

(Last revised 2008-07-16 15:30 UTC)

Relevant documents

  1. Front end #1 PAI data: FEND-40.00.00.00-116-A-REP.pdf
  2. band 3 PAI (cartridge #3): FEND-40.02.03.00-133-A-REP.pdf
  3. band 6 PAI (cartridge #3): FEND-40.02.06.00-214-B-TDR.pdf
  4. band 7 PAI (cartridge #1): FEND-40.02.07.00-0010-B-REP.pdf
  5. band 9 PAI (cartridge #1): FEND-40.02.09.00-044-B2-REP+cartridge+acceptance+test+report+SN001.doc

  6. Ticra report (we use efficiency equations on page 118 et seq ) secret document _DO NOT distribute further_ chapter 5 attached other sections at under appendices 1-11
    (This is an EDM reference. Available also in the "Optical Analysis Final Report Chapter 5" below.)

    Other documents:

  7. Latest beam scans of bands 3 and 6 using the NSI scanner after alignment: FEND-40.09.07.00-074-A-REP.pdf
  8. NA FEIC Preliminary Beam Measurements: FEND-40.09.03.00-041-A-REP.pdf

  9. How we analyse data: ALMA-40.00.00.00-123-A-PRO.doc

  10. Test setup: FETMSdescription7.pdf
  11. Block diagram: 20080402_Block+Diagram+of+NA+FEIC+system+without+LORTM.pdf

    Test set data

  12. Beam scanner doc
  13. FEIC discussion measurements
  14. Band 6 comparison
  15. FEND report
  16. 1433_001.pdf

    17. Further notes

  17. 2007-10-04 Optical Analysis Final Report Chapter 5
  18. Optics section from FE acceptance (24 MB)
  19. Baryshev beam efficiency presentation
  20. Far field distances (PDF) or (Excel .xls) from Richard, who says:
    I have made the attached table to show the Rayleigh distances for the ALMA bands. This assumes a Gaussian beam and a 12 dB taper. The Rayleigh distance is defined as pi*w_02/lambda with w_0 being the beam waist radius.

    21. CSV and other data from Geoff and others

  21. Data files from Geoff
  22. Geoff's Powerpoint presentation from our 2008-05-27 telecon
  23. Plots of Geoff's data, from Todd
  24. Todd's plots of data with model fits
  25. Fred's FFT of NSI NF data
    Fred comments:   The first pair of plots is a re-display of the near-field amplitude and phase as measured by the NSI scanner. The x and y axes are labeled in mm. The second pair of plots shows the amplitude and phase patterns of a straight FFT of the near-field data. The units for the axes here are degrees (assuming I computed the grid spacing correctly - which I need to double check). The final pair of plots show, for comparison, the far-field distribution computed by the NSI software, over the range -10 deg to 10 deg.
  26. Todd's plots of Geoff's lambda/4 shifted data, 2007 Scan 13
  27. Todd's plots of Geoff's lambda/4-shifted data, 2008 Scan 20
    The above plots are from Geoff's data with lambda/4-shifts, currently entries 26-37 in the list of data files.
    Todd said: Here are two PDFs, each with six panels, illustrating these 12 data files. The 2D Gaussian fit parameters are listed under the amplitude panels.
  28. Scan 20 with mask before FFT Todd said:
    In today's meeting, you asked that we compare the FFT of the nearfield data taken above and below the point in elevation where the anomalous appearance tends to manifest itself (y > 0.21). In the enclosed plot of 2008_Scan_20, we compare the FFT using the whole data vs. using only the cleaner area below this line. The right column is simply a zoom of the middle column. Clearly, there is much less large scale structure when the top part is masked. Also, note the point-like features at (-34,-33deg) and (-34,+27deg) which appear more prominently in the unmasked data, and are nearly symmetric with respect to the beam center ~ (0,-2). I wonder if these could be somehow related to the mechanical corner struts of the xy stage? However, the scale may not be right for this to be the case: (200mm)(tan34) = 135mm. We also examined the FFT of just the upper section of data, and this showed some of the excess in the upper two quadrants, but with lower S/N.
  29. Scan 20 with complementary mask before FFT
  30. Spreadsheet from Richard Richard says:
    Here is a cleaned-up version of my spread-sheet, doing just the spill-over calculation on the Far Field data. On the Scan 77 case that we have been taking as a reference I get 2.91% as the minimum spillover - optimizing just for that - and 3.00% with the secondary at (0, -1.0) deg.
  31. Spreadsheet for phase fitting, from Richard (Excel, 27 MB).
  32. Subreflector patterns, Spreadsheet from Sri.
  33. Subreflector spreadsheet for Scan 77 Sri said:
    Attached excel file has subrefl. scattered pattern thru different cuts. The taper at 64 deg. varies from -17 dB at -90 deg. to -11 dB at +90 deg. The 90 deg. plane is the plane of offset of the Band 9 cartridge and the cartridge offset is in the -Y direction (-50mm).
  34. Far field fits summary. Richard says:
    I have run through the remaining data sets and put the results in the attached. In some places the consistency of the results in encouraging, in others less so.
  35. 2008 Scan 20, spurious feature identified (Darrel) Last revised 2008-06-25 The near-field data of Scan 20 have been filtered to enable identification of the origin of the spurious far-field feature in this scan already identified from Todd and Fred's analyses.
  36. ftp://ftp.cv.nrao.edu/NRAO-staff/fschwab/fftplots.ps FTP link to Fred's FFT files. NB, 70+ MB . or Much smaller version here: jpeg files zipped.
    Fred says:
    I fft'd the near-field patterns for Beam 1 and Beam 2 separately, and found that the spurious feature is much more compact and well-defined in the plots of those data than in the plots with both beams combined, where it appears more diffuse. I also noted that for Scan 20 there is a feature at the top and very center of the the fft plot (actually in these cases, two small blobs slightly separated), and that in fact there are similar features - at the top for the 2008 data, and at the bottom for the 2007 data - in every scan. I think these features are spurious and likely arise from the putative backlash. I've done the fft for every one of the data sets. (If you use ghostview to view these, you'll likely see some artifacts which disappear if you turn OFF ghostview's Antialiasing option. They may show up with other viewers also, but they don't show up if you send the file to a printer.) Scan 4 from 2008 in the near-field phase plot shows very strong horizontal striations. In my FFT amplitude plot, note the intensity of the pink blob at the very top. I should mention that in the fft plots the coordinates on the plots now are u and v. (Richard had questioned me and Geoff on this matter.)
  37. Calculation of efficiencies revised 2008-06-22 from Richard Hills (PDF) or Word .doc format.
  38. Beam efficiency Spreadsheet 2007 7.xls Modified spreadsheet from Richard Hills
  39. fit-all-2007_small_A.xls Richard's spreadsheet on the same data
    Richard describes the above two spreadsheets: I put in the 0.1-degree resolution data that you [Josh] sent and got the sheet working. There were still some discrepancies with my numbers so I had a poke around and found a few problems. I have marked them and made modifications. This now agrees with my sheet for the particular set of numbers that have been assumed for the phase centre. (I haven't tried to figure out how the macros work.)
    If you fit for the best phase centre the phase efficiency increases from 0.9920 to 0.9953. More importantly the phase centre shifts by a further (0.38,1.69,-24.22). To me this says that we do need to do a proper fit if we are to use these values to anything secure about beam squint, etc.
  40. Patterns and efficiencies at 94 GHz from Sri. Sri said:
    Josh gave me data on Band 3 Scan 17. I used Polarization 1 data to calculate the subreflector scattered pattern and the telescope beam. Since, setting up the geometry for Band 3 is complex, I first did my calculations with the Band 3 window on axis of the telescope. So for this case the subreflc. is not tilted. Then I did the Band 3 actual case where the window is off set by 18.1 cms and the subreflector is tilted by 0.881 deg.
    Summary, Band 3 Scan 17 (Word)
    There are 4 exl files.
    1. 94P1abs.xls Subrefl pattern for window on axis
    2. 94P1abm.xls Telescope beam for window on axis
    3. 94P1efs.xls Subrefl pattern for window off axis
    4. 94P1efm.xls Telescope beam for window off axis.
    In 94P1efm.xl the patterns for on axis and off axis are overlaid on a single graph. The Off case beam looks good and there is only 1.1% loss for this case. Sri.
  41. Josh compilation of data in accordance with the list Geoff gave.
    The list is included.
  42. Comments from Darrel on the necessary sampling interval for near-field beam scanner. 0.4*lambda is a good value.
  43. Beam Efficiency Spreadsheet Revised 2007 17.xls Richard commented:
    I have edited the scan 17 version to have names consistent with the TICRA report and the revised version of my note.
  44. Josh has put the current band 3 scan results here as a spreadsheet. Josh will update this sheet as more data become available.
  45. Geoff supplied 4 new data files:
    1. Scan_100_Beam_1.csv
    2. Scan_100_Beam_2.csv
    3. Scan_109_beam_1.csv
    4. Scan_109_beam_2.csv
    Geoff explains:
    [I attach] the files for the scans 100 and 109 (each was at two z's so I send both scans separately - not combined)
    100 is WITH the warm optics
    109 is WITHOUT warm optics - I scanned the same area so I missed the peak.
    The values are normalized to the peak value seen in the scan area. For 109 the peak in area is -60.2 dBm. When I went to the signal maximum it has -28.2 dBm ( so everything is 32 dB down or more) (The peak in scan 100 is -26.49 dBm)
  46. Geoff added plots of the above scans:
    1. NF scans 100 & 109 (.xls) . NB large, ~11 MB file .
    2. Darrel created a smaller, PDF version of the large xls file: NF scans 100 & 109 (.PDF file)
    3. Geoff also gives details of the feed horns used as sources: Source feed horns (.doc file) .
    Geoff said of the above files:
    I attach plots of the 4 scans I sent earlier.
    The values are normalized to the peak value seen in the scan area (thanks to the NSI software). For 109 the peak in area is -60.2 dBm. When I went to the signal maximum it has -28.2 dBm ( so everything is 32 dB down or more -the light red being another 10-12 dB down = -42dB) (The peak in scan 100 is -26.49 dBm)
    There is some change with z distance.
    I also attach details on the feed horns used on the sources for the various bands
  47. Comments and questions from Richard, July 4th
    1. Source feed horns comments
    2. Item list plus interchanges
  48. Some earlier correspondence from Bernard Lazareff
    1. 2008-02-12
    2. 2008-02-20
    3. 2008-02-21
    4. another 2008-02-21
    5. 2008-05-29
  49. Notes from 2008-07-11 telecon
  50. First version of Baryshev report from Geoff - still missing quite a few sections and any useful numbers.