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Kirkby calibration kit alternatives?
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hendorog:
Best one so far - in terms of residual. I opened up the Z0 limit, to range from 48 to 52 ohms.


--- Code: ---Optimization results:
offs_delay = 55.465329 ps
offs_loss = 5.685029 Gohm/s
offs_Z0 = 49.172627 ohm
C0 = -286.232017 * 1e-15 F
C1 = -2372.098441 * 1e-27 F/Hz
C2 = 1891.981433 * 1e-36 F/Hz^2
C3 = -246.050762 * 1e-45 F/Hz^3

Residual RMS error : -62.879680 dB

--- End code ---
G0HZU:
The last two look the best but I'm not sure if I'm modelling the offset Zo correctly. I found that tweaking Zo improved the male SHORT Kirkby kit and that was the thing I would have experimented with if I had this kit here as per post #53.

Are you optimising to 3GHz or 6GHz? Your data looks flat to 3GHz but there is a tiny slope up to 6GHz. But it still looks good.

However, some of your values look strange. Normally the fringing capacitance is about 50fF but your optimiser has put in a negative capacitance of -286fF. I guess that will still be OK in the world of mathematics but can you set realistic limits for this capacitance of maybe 30fF to 100fF and run it again?

On the Agilent kit this capacitance only varies by a tiny amount away from 50fF across frequency.
hendorog:

--- Quote from: G0HZU on February 24, 2018, 11:49:48 pm ---The last two look the best but I'm not sure if I'm modelling the offset Zo correctly. I found that tweaking Zo improved the male SHORT Kirkby kit and that was the thing I would have experimented with if I had this kit here as per post #53.

Are you optimising to 3GHz or 6GHz? Your data looks flat to 3GHz but there is a tiny slope up to 6GHz. But it still looks good.

--- End quote ---

By default it is sweeping over the range in the Dr Kirkby S1P file - from 50MHz to 12GHz.


--- Quote ---However, some of your values look strange. Normally the fringing capacitance is about 50fF but your optimiser has put in a negative capacitance of -286fF. I guess that will still be OK in the world of mathematics but can you set realistic limits for this capacitance of maybe 30fF to 100fF and run it again?

On the Agilent kit this capacitance only varies by a tiny amount away from 50fF across frequency.

--- End quote ---

No problem, I'll constrain the C values to that range and run it again. Could be just that the Dr Kirkby standards are not as mechanically 'refined' as the Agilent ones?
G0HZU:
Here's what appears to be the custom coefficients for that Kirkby female OPEN and C0 looks to be about 44fF.


--- Quote ---Female open. (Use OPEN(M) or OPEN -F- depending on model of VNA - see notes above) **
Minimum frequency:  0 GHz
Maximum frequency:  7.0 GHz
Offset Zo: 50.0 ohms
Offset loss: 3.0  G ohm/s
Offset delay: 39.8  ps
C0: 44.36
C1: 156.42
C2: 1159.1
C3: -131.92


--- End quote ---


I just spotted your attached results files.

The optimiser tool you are using looks very powerful. I tried downloading it and the other sparam tool etc and I already have GNU Octave but I wasn't sure what to type in the command line. I tried an edited version of the default example but it didn't like it. I'm a newbie with GNU Octave so I probably haven't installed something correctly. I assume all the plots come from this optimiser tool?
G0HZU:
Try running it up to 6GHz or maybe 7GHz as Fmax. It might give a flatter result?
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