Reference Cavity

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

Monopole Mode

RefTrans.png

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

  • 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 /GHzSorted ascending Unloaded Q External Q Loaded Q Loaded Q check
S11 14.772 1407 2814 938 938
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.
  • Need to simulate to determine why the external Q factor is high, what can be done to correct this.

Position Cavity

  • This time the correct feedthroughs were used.

trans.png

S Parameter Frequency /GHz Loaded Q
S21 14.996 809
S32 14.995 878
S43 14.996 811
S14 14.995 874

  • 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
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

  • 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

cc.png

S Parameter S21 S32 S43 S14
Maximum Signal /dB -43.9 -51.1 -44.3 -48.6

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

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Topic revision: r3 - 28 Aug 2014 - JackTowler

 
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