Products > Test Equipment
Kirkby calibration kit alternatives?
小太:
Here are the fitted values by METAS VNA Tools for the entire 0~18GHz range.
The Applied EM kit is only specified up to 10GHz though, so this is just for educational purposes and not a commentary about the kit quality :)
(I'll do a proper 0~10GHz version in my next post)
Results have been plotted in Mathematica with equations from Keysight application note 1287-11 "Specifying Calibration Standards and Kits".
"Given" values are those included with the Applied EM kit (as reported here), while "Fitted" are those VNA Tools generated
Short FOffset Z0
(Ω)Offset delay
(ps)Offset loss
(GΩ⋅s-1)L0
(10-12 H)L1
(10-24 H⋅Hz-1)L2
(10-33 H⋅Hz-2)L3
(10-42 H⋅Hz-3)Given51.5683.612.57-889.079989.259983.11-1413.8Fitted51.52481.1396.2800-909.96111076-14204340.48Open FOffset Z0
(Ω)Offset delay
(ps)Offset loss
(GΩ⋅s-1)C0
(10-15 F)C1
(10-27 F⋅Hz-1)C2
(10-36 F⋅Hz-2)C3
(10-45 F⋅Hz-3)Given5076.371.96-351.35-39471326.61-507.08Fitted53.54967.4422.787146.597-9005010138-358.16Load FOffset Z0
(Ω)Offset delay
(ps)Offset loss
(GΩ⋅s-1)Given54.164.7710Fitted54.2538.4764-11.561
P.S., Equations from Keysight application note 1287-11 converted to Mathematica form
--- Code: ---Zr = Quantity[50, "Ohms"];
(* Equations 1.1 and 1.4 *)
\[Gamma]l = \[Alpha]l + I \[Beta]l;
\[CapitalGamma]1 = (Zc - Zr)/(Zc + Zr);
\[CapitalGamma]T = (ZT - Zr)/(ZT + Zr);
\[CapitalGamma]i = (\[CapitalGamma]1 (1 - Exp[-2 \[Gamma]l] - \[CapitalGamma]1 \[CapitalGamma]T) + Exp[-2 \[Gamma]l] \[CapitalGamma]T)/(1 - \[CapitalGamma]1 (Exp[-2 \[Gamma]l] \[CapitalGamma]1 + \[CapitalGamma]T (1 - Exp[-2 \[Gamma]l])));
(* Equation 1.10 *)
\[Alpha]l = (offsetLoss offsetDelay/(2 offsetZ0)) Sqrt[f/Quantity["Gigahertz"]];
\[Beta]l = 2 \[Pi] f offsetDelay + \[Alpha]l;
Zc = offsetZ0 + (1 - I) (offsetLoss/(4 \[Pi] f)) Sqrt[f/Quantity["Gigahertz"]];
(* Equations 1.12 and 1.13 *)
ZS = I 2 \[Pi] f (L0 + L1 f + L2 f^2 + L3 f^3);
ZO = 1/(I 2 \[Pi] f (C0 + C1 f + C2 f^2 + C3 f^3));
(* Example usage with OPEN parameters *)
\[CapitalGamma]i /. ZT -> ZO /. {
C0 -> Quantity[46.597 10^-15, "Farads"],
C1 -> Quantity[-90050 10^-27, "Farads"/"Hertz"],
C2 -> Quantity[10138 10^-36, "Farads"/"Hertz"^2],
C3 -> Quantity[-358.16 10^-45, "Farads"/"Hertz"^3],
offsetDelay -> Quantity[67.442, "Picoseconds"],
offsetLoss -> Quantity[2.7871, "Gigaohms"/"Seconds"],
offsetZ0 -> Quantity[53.549, "Ohms"],
f -> Quantity[f, "Gigahertz"]
};
S11 = % /. Cases[Variables[%], v_ /; Head[v] =!= Quantity -> v -> Quantity[v, "DimensionlessUnit"]] /. {
Quantity[v_, "DimensionlessUnit"] :> v,
Quantity[v_, 1/"DimensionlessUnit"] :> v,
Quantity[v_, Sqrt["DimensionlessUnit"]] :> v
};
Plot[Abs[S11], {f, 0, 18}, AxesLabel -> {"Frequency (GHz)", "|S₁₁|"}]
--- End code ---
小太:
Same thing as above, but fitting was limited to just 0~10GHz
Short FOffset Z0
(Ω)Offset delay
(ps)Offset loss
(GΩ⋅s-1)L0
(10-12 H)L1
(10-24 H⋅Hz-1)L2
(10-33 H⋅Hz-2)L3
(10-42 H⋅Hz-3)Given51.5683.612.57-889.079989.259983.11-1413.8Fitted52.31985.3251.0887-965.37-6172329349-2997.3Open FOffset Z0
(Ω)Offset delay
(ps)Offset loss
(GΩ⋅s-1)C0
(10-15 F)C1
(10-27 F⋅Hz-1)C2
(10-36 F⋅Hz-2)C3
(10-45 F⋅Hz-3)Given5076.371.96-351.35-39471326.61-507.08Fitted52.27777.4471.2253-309.12-12284219.52-456.68Load FOffset Z0
(Ω)Offset delay
(ps)Offset loss
(GΩ⋅s-1)Given54.164.7710Fitted 1*77.7750.76737340.06Fitted 2*54.1426.239110.000
* The "Load F" fitting decided to produce stupid values initially, so I ran it again but forced the offset loss to 10, and it gave more reasonable values. Both results are shown
I'm not really qualified to make a conclusion here (I'm too inexperienced), but if I were to make one anyways:
- Assuming the VNA was calibrated correctly with the Rosenberger kit (and kit was within spec)
- Applied EM's short and open have calibration coefficients that seem fitted to a max of 6~8GHz rather than all the way up to 10GHz
- Applied EM's load coefficients seem to be way off
- Ignoring the load coefficients (I haven't worked out how to apply them to measured data yet), the load only has a return loss of ≥36dB up to 4GHz, and it progressively gets worse until 29dB at 10GHz, which doesn't sound like it's within spec
EE-digger:
You can also ask yourself how good your results have to be. I've done a lot of chip antenna layout and tuning work. After cal to the end of my VNA cable with SMA standards, I still have to extend it over an SMA to U.FL to another U.FL on the pcb.
In a case like this, you're better off creating your own open, short load on the pcb itself. Then, just put an RF short on the last connector and run auto or manual compensation for the short.
added - and, of course the frequencies you're working on will affect this big time
joeqsmith:
--- Quote from: radar_macgyver on February 08, 2024, 09:14:11 pm ---I quit after tearing my hair out for a good 2 hours trying to figure out the METAS tools, so if someone else can use it to generate a model I'd be grateful (and maybe post a link to a tutorial?)
--- End quote ---
Sorry for the necropost. I had watched the METAS video and they did not go into any details on how to accomplish this. Going through this thread, I too am curious how to derive the coefficients for an unknown set.
The last time I did this, I used one of the local members Matlab scripts. I would like to try this with METAS. Any pointers to save my hair are appreciated.
Also:
https://www.eevblog.com/forum/testgear/kirkby-calibration-kit-alternatives/msg1437115/#msg1437115
SUJ, nice job with the waveguides. I am on a similar path.
shabaz:
Not read the entire thread (too long!) but I was in a situation where I had an OK-ish quality, new OSL Tee, but without the coefficients. I asked Dr. Kirkby nicely, and he was kindly willing to measure it and provide the coefficients for me. The price was extremely reasonable (this was about five years ago). So, that might be an option for the cases where someone's ended up with a cal kit (say from eBay) which might accidentally be missing the data.
Recently I've been using the SDR-kits cal kit (PDF doc), but have not exercised them beyond 1 GHz yet. The kit is not bad for what it is, however, the supplied 50-ohm load in my case had 48.52 ohm DC resistance. That's normally not an issue (there's another thread on the topic elsewhere) and some VNAs allow for entering that value, but if that's a concern (personally, I wanted closer to 50 ohm because I also tend to use it for various purposes at low frequencies, from DC to tens of kHz) then the very easy solution is to just replace that with your own 50-ohm load, e.g. Huber & Suhner ones are often much closer at DC.
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