Intro

    On 10feb23  Felix measured the s-parameters for the wide band receiver. The setup was:

• The receiver was in the lab and cooled.
• absorber was placed in front of the window.
• the field fox was used to do the 2 port measurement,.
• s1 input : cal sma input on dewar
• s2 output: lna sma output
  
• the s-parameters  were measured between 2 and 14 GHz. 1001 channels were used.
• the reference plane was the cal sma input ant the lna sma output.
  

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The S-parameters:

    Plots show the

• The s-parameters: s21 s11,s22,s12  
  
• The acf computed from each sparameter spectra
• The acf was computed as:  abs(fft(spc))[0:lenfft/2-1] (since it is symmetric)
• I then divided by acf[0] (the 0 lag which is the integral of the power across the spectra)
• May be off by a factor of 2 since the negative lags were ignored.
• The lag axis was:
• max Bw:14-2 GHz = 12GHz
• shift rate: 1/12GHz (.083 ns resolution)
• max lagdelay: .083*500=41 ns.
  
• The signal path is:
• Cal sma input
• 10db pad
• coupled input (20db )
• highpass filter
• lna
• output
  

    The plots show the measured s-parameters (.ps) (.pdf):

• Black is polX, red is polY
• Page 1: S21 : gain: input cal port, output lna output
• Top S21 gain:
• there is 10+20db of attenuation from pad, coupler
• the cumulative gain is
  
• polX: 7db at 2.5 ghz to 0db at 14 GHz
  
• polY: 3db at 2.5 ghz to 0db at 14GHz
  
• the amp gain (measured by hamdi)
  
• polX 40db at 2.5 GHz to 36 db at 14Ghz
• polY  35db +/- 1db 2.5 to 14 GHz,.
• Bottom: acf of S21
• there is ripple power at 5 to 7 ns.
• Page 2: S11: reflections at cal input.
• Top: spectra of S11
• The level stays below -10 except for some of the ripples from 9 to 11 GHz
• Bottom: acf of S11
• there are some very sharply defined ripples
• 3ns
• 6ns
• 17.5, 19.5,22 25.5ns
• The acf has been normalized to the total power.
• PolX and polY show very similar ripples.
  
• The 10db pad should knock down any reflections beyond the pad by 20db.
• a 6ns ripple with cable velocity of .7 would be a distance of .63 meters (about 2 feet).
• Page 3: S22: reflections at lna output
• Top: spectra of S22
• values range from -20db to -15 db (with some oscillations going higher).
• Bottom:acf of s22
• ripples similar to S11 with a few added frequencies,.
• Page 4: S12: lna output to cal input.
• Top spectra
• < -70db
• Bottom: acf
• no ripples stand out
• Page 5: plot ACF's for all parameters on 1 page.
• I plotted the Acf on 1 page to compare the freq ripples
• I converted the x axis to distance using .15 m/ns
• these distances assume the velocity is c. The should be multiplied by the velocity in the cables (say .7)
• S11 and S22 show some of the same ripples.
  

   

SUMMARY:

• The sparameters from the cal input to the lna output were measured.
• Ripples were seen (especially in S11 and S22)
• the times for the ripples were longer than expected (if just looking at the cable lengths)
• You would have though that the 10db pad between the sma input and the coupler would have done a better job cutting down the ripples.
  

processing: x101/230213/sparmswbrcv.pro