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Optimum Line length Verification for TRL cal

Question asked by GS on Nov 6, 2007

I am trying to create a TRL standard and I calculated the line offset between the through and the line standard as follows to achive the 20-160 degree phase offset:

Eeff = 2.84 (Effective dielectric constant)
f1 = 1000 ( low end of the band in MHz)
f2 = 6000( High end of the band in MHz)
fc = (f1+f2)/2 ( Centre of the band)

VF = 1/sqrt(Eeff) ( Calculating the velocity factor)

Calculated the Electrical length using  the Agilent  app note 5968-5329E  page 22 as a reference document :

El= (15000*VF)/(f1+f2) 
El in mils = El* 393.700 =  500.33 mils

Then I verified whether the offsets were met by using the follwing equations:
Phase1 = (0.012*f1*El)/VF = 25.7 Degrees
Phase2 = (0.012*f2*El)/VF= 154.28 Degreed
PhaseC= (0.012*fc*El)/VF= 90 Degrees

Which is well within the specified range.

Now the problem I have is when I tried to verify this in using Agilent Momentum. I simulated the through line (2822 mils) and then I simulated the line standard (2822+500.33 =3322 mils) and looked at the Phase Vs frequency of S21.

I assumed that at  the centre band I would see a 90 degree difference between tha phase plots, and at the high end of the band (6000 MHz) I would see a 160 degree difference in the phase plots. but I do NOT see that difference in phase.

So could you please suggest a way to verify the line standard??

Thanking you greatly GS