Difference: ClicBrazeRF (1 vs. 4)

Revision 422 Oct 2014 - JackTowler

Line: 1 to 1
 
META TOPICPARENT name="NewClicBpm"

Reference Cavity

Revision 328 Aug 2014 - JackTowler

Line: 1 to 1
 
META TOPICPARENT name="NewClicBpm"

Reference Cavity

Line: 23 to 23
 
S22 14.772 1313 3283 938 938

  • The unloaded Q factor is higher than before brazing, however the external Q is larger, making the Q factor larger than 500.
Added:
>
>
  • Need to simulate to determine why the external Q factor is high, what can be done to correct this.
 

Position Cavity

Line: 47 to 48
 
S33 14.996 1200 2222 779 779
S44 14.995 1394 2221 857 857
Changed:
<
<
  • The external Q is not as higher as before but still much larger than the value in simulation, ~600.
>
>
  • The external Q is not as high as before but still much larger than the value in simulation, ~600.

  • Need to simulate to determine why the external Q factor is high, what can be done to correct this.
 

Cross Coupling

Line: 57 to 60
 
Maximum Signal /dB -43.9 -51.1 -44.3 -48.6

  • All maximum cross couplings are below -40 dB.
Added:
>
>
  • Much lower (remarkably lower) than measured previously.
 

Revision 221 Aug 2014 - JackTowler

Line: 1 to 1
 
META TOPICPARENT name="NewClicBpm"

Reference Cavity

  • The BPM was connected to 2 ports of the VNA and S parameters were measured.
Added:
>
>
  • Vacuum seals were used this time.
 

Monopole Mode

Line: 12 to 13
 
Frequency /GHz 14.772 14.772
Loaded Q 943 953
Changed:
<
<
  • The measured resonant frequency is 300 MHz below the desired 15 GHz.
  • The feedthrough antennae were not well concentrically aligned and frequency was seen to vary on repeated repositioning of the feedthrough.
  • Simulations need to be performed to see if this effect is reproduced.
>
>
  • The measured resonant frequency is 230 MHz below the desired 15 GHz. But has increased 70 MHz after brazing.
 
  • The Q values can be determined by plotting a smith chart.

RefSmithFinal.png

S Parameter Frequency /GHz Unloaded Q External Q Loaded Q Loaded Q check
Changed:
<
<
S11 14.698 382 588 231 231
S22 14.699 426 530 238 236
>
>
S11 14.772 1407 2814 938 938
S22 14.772 1313 3283 938 938
 
Changed:
<
<
  • The unloaded Q factor is much smaller than expected, bringing the loaded Q down.
  • This could be caused by uneven clamping or not clamping strong enough or by excessive surface roughness.
  • The frequency and Q factor was seen to vary with antenna offset, so the effect of this offset needs to be investigated.

Feedthrough Offset Variation

  • Simulations were performed with the feedthrough offset 1 degrees the along the beam pipe direction.
  • Corresponding to a antenna tip movement range of 0.26 mm within the cavity.
  • Positive values correspond to offsets towards the flat surface of the cavity, negative values correspond to offsets towards the reentrant part of the cavity.

Offset Angle /degrees Frequency /GHz Q_0 Q_ext Q_L
-1.5 14.736 2739 203 189
-1.0 14.743 2732 194 181
-0.5 14.751 2730 193 180
0.0 14.760 2727 197 184
0.5 14.771 2724 210 195
1.0 14.780 2722 230 212
1.5 14.794 2715 260 237

OffsetSim.png

  • The frequency change depending on the antenna offset is ~700MHz/mm.
  • The Q factor change is not enough to explain the low loaded Q factor of the position cavity.

Dipole Mode

dipole.png

S Parameter
<-- -->
Sorted ascending
Frequency /GHz Loaded Q
S11 19.090 98
>
>
  • The unloaded Q factor is higher than before brazing, however the external Q is larger, making the Q factor larger than 500.
 

Position Cavity

Changed:
<
<
  • The BPM was clamped as above and all four ports connected to the VNA.
  • A drop in frequency from 15 MHz was predicted from simulation.
>
>
  • This time the correct feedthroughs were used.
  trans.png

S Parameter Frequency /GHz Loaded Q
Changed:
<
<
S13 14.988 1434
S24 14.991 1545
>
>
S21 14.996 809
S32 14.995 878
S43 14.996 811
S14 14.995 874
 
Changed:
<
<
  • The frequencies are very close to the expected value of 14.985 GHz, the Q factors are three times larger.
  • The coupling here is too weak to rely on the Q factors calculated from the Smith chart but it does offer clues to the source of the high loaded Q.
>
>
  • The frequencies are higher than the pre-brazing value of ~14.990 GHz, but just below 15 GHz.
  • The Q is closer to the design value, but still too high.
  PosSmith.png

S Parameter Frequency /GHz Unloaded Q External Q Loaded Q Loaded Q check
Changed:
<
<
S11 14.988 1733 7888 1421 1420
S22 14.991 2026 6246 1537 1530
S33 14.988 1713 8327 1427 1421
S44 14/991 1647 13628 1462 1469

  • The external Q is much higher than the design value of ~600, possibly caused by the incorrect coupler.

Position Cavity with Reference Cavity Antenna

>
>
S11 14.996 1154 2450 789 789
S22 14.995 1250 2999 869 882
S33 14.996 1200 2222 779 779
S44 14.995 1394 2221 857 857
 
Changed:
<
<
  • The position cavity was simulated with the feedthrough antenna from the reference cavity.

Frequency /GHz Unloaded Q External Q Loaded Q
14.983 3309 3192 1625

  • In the simulation the external Q is much larger than expected, driving the loaded Q up.
  • The value of the loaded Q is closer to that measured from the transmission curves.
  • This is encouraging evidence that using the correct feedthroughs and vacuum seal will results in Q's close to the design values.
>
>
  • The external Q is not as higher as before but still much larger than the value in simulation, ~600.
 

Cross Coupling

cc.png

S Parameter S21 S32 S43 S14
Changed:
<
<
Maximum Signal /dB -30.9 -31.0 -39.8 -36.8
>
>
Maximum Signal /dB -43.9 -51.1 -44.3 -48.6
 
Changed:
<
<
  • All maximum cross couplings are below -30 dB.
>
>
  • All maximum cross couplings are below -40 dB.
  \ No newline at end of file
Added:
>
>
META FILEATTACHMENT attachment="cc.png" attr="h" comment="" date="1408631223" name="cc.png" path="cc.png" size="70682" user="ztap061" version="1"
META FILEATTACHMENT attachment="trans.png" attr="h" comment="" date="1408631223" name="trans.png" path="trans.png" size="54912" user="ztap061" version="1"
META FILEATTACHMENT attachment="RefSmithFinal.png" attr="h" comment="" date="1408631223" name="RefSmithFinal.png" path="RefSmithFinal.png" size="87228" user="ztap061" version="1"
META FILEATTACHMENT attachment="RefTrans.png" attr="h" comment="" date="1408631223" name="RefTrans.png" path="RefTrans.png" size="44179" user="ztap061" version="1"
META FILEATTACHMENT attachment="PosSmith.png" attr="h" comment="" date="1408631386" name="PosSmith.png" path="PosSmith.png" size="96031" user="ztap061" version="1"

Revision 121 Aug 2014 - JackTowler

Line: 1 to 1
Added:
>
>
META TOPICPARENT name="NewClicBpm"

Reference Cavity

  • The BPM was connected to 2 ports of the VNA and S parameters were measured.

Monopole Mode

RefTrans.png

S Parameter S12 S21
Frequency /GHz 14.772 14.772
Loaded Q 943 953

  • The measured resonant frequency is 300 MHz below the desired 15 GHz.
  • The feedthrough antennae were not well concentrically aligned and frequency was seen to vary on repeated repositioning of the feedthrough.
  • Simulations need to be performed to see if this effect is reproduced.
  • The Q values can be determined by plotting a smith chart.

RefSmithFinal.png

S Parameter Frequency /GHz Unloaded Q External Q Loaded Q Loaded Q check
S11 14.698 382 588 231 231
S22 14.699 426 530 238 236

  • The unloaded Q factor is much smaller than expected, bringing the loaded Q down.
  • This could be caused by uneven clamping or not clamping strong enough or by excessive surface roughness.
  • The frequency and Q factor was seen to vary with antenna offset, so the effect of this offset needs to be investigated.

Feedthrough Offset Variation

  • Simulations were performed with the feedthrough offset 1 degrees the along the beam pipe direction.
  • Corresponding to a antenna tip movement range of 0.26 mm within the cavity.
  • Positive values correspond to offsets towards the flat surface of the cavity, negative values correspond to offsets towards the reentrant part of the cavity.

Offset Angle /degrees Frequency /GHz Q_0 Q_ext Q_L
-1.5 14.736 2739 203 189
-1.0 14.743 2732 194 181
-0.5 14.751 2730 193 180
0.0 14.760 2727 197 184
0.5 14.771 2724 210 195
1.0 14.780 2722 230 212
1.5 14.794 2715 260 237

OffsetSim.png

  • The frequency change depending on the antenna offset is ~700MHz/mm.
  • The Q factor change is not enough to explain the low loaded Q factor of the position cavity.

Dipole Mode

dipole.png

S Parameter Frequency /GHz Loaded Q
S11 19.090 98

Position Cavity

  • The BPM was clamped as above and all four ports connected to the VNA.
  • A drop in frequency from 15 MHz was predicted from simulation.

trans.png

S Parameter Frequency /GHz Loaded Q
S13 14.988 1434
S24 14.991 1545

  • The frequencies are very close to the expected value of 14.985 GHz, the Q factors are three times larger.
  • The coupling here is too weak to rely on the Q factors calculated from the Smith chart but it does offer clues to the source of the high loaded Q.

PosSmith.png

S Parameter Frequency /GHz Unloaded Q External Q Loaded Q Loaded Q check
S11 14.988 1733 7888 1421 1420
S22 14.991 2026 6246 1537 1530
S33 14.988 1713 8327 1427 1421
S44 14/991 1647 13628 1462 1469

  • The external Q is much higher than the design value of ~600, possibly caused by the incorrect coupler.

Position Cavity with Reference Cavity Antenna

  • The position cavity was simulated with the feedthrough antenna from the reference cavity.

Frequency /GHz Unloaded Q External Q Loaded Q
14.983 3309 3192 1625

  • In the simulation the external Q is much larger than expected, driving the loaded Q up.
  • The value of the loaded Q is closer to that measured from the transmission curves.
  • This is encouraging evidence that using the correct feedthroughs and vacuum seal will results in Q's close to the design values.

Cross Coupling

cc.png

S Parameter S21 S32 S43 S14
Maximum Signal /dB -30.9 -31.0 -39.8 -36.8

  • All maximum cross couplings are below -30 dB.

<--

Settings just to customise this page

-->
 
This site is powered by the TWiki collaboration platform Powered by PerlCopyright © 2008-2022 by the contributing authors. All material on this collaboration platform is the property of the contributing authors.
Ideas, requests, problems regarding RHUL Physics Department TWiki? Send feedback