My collegues and I are using a 4-port N5241A with the FCA, IMDx and NFx options to test frequency converters; we're making all of our measurements using the SMC + phase approach. My task is to create and maintain the cal sets for several state files; we're measuring parameters such as group delay, conversion gain/loss, RF/IF port return loss, 3rd order intermods and noise figure.

I'm using a 4-port 3.5mm E-CAL, a 18GHz USB power sensor and a 346B noise source to perform all of the calibrations. I used a 26.5GHz comb generator to generate a phase reference calset which I've applied to the group delay state file's calset.

Our customer wants the uncertainty specs for all of our measurements. Naturally I was assigned the task of obtaining these specs...lucky me! My first approach was to use the network analyzer uncertainty calculator; however, to my dismay, I found that the calculator does not include uncertainties for SMC + phase measurements! So, I then looked at the data sheet for the N5241A and found, again to my dismay, there weren't any uncertainty specs for SMC + phase measurements in there either!

So, if anyone out there knows how to compute these uncertainty specs or knows where to find them, it would be greatly appreciated!

-Dan

I'm using a 4-port 3.5mm E-CAL, a 18GHz USB power sensor and a 346B noise source to perform all of the calibrations. I used a 26.5GHz comb generator to generate a phase reference calset which I've applied to the group delay state file's calset.

Our customer wants the uncertainty specs for all of our measurements. Naturally I was assigned the task of obtaining these specs...lucky me! My first approach was to use the network analyzer uncertainty calculator; however, to my dismay, I found that the calculator does not include uncertainties for SMC + phase measurements! So, I then looked at the data sheet for the N5241A and found, again to my dismay, there weren't any uncertainty specs for SMC + phase measurements in there either!

So, if anyone out there knows how to compute these uncertainty specs or knows where to find them, it would be greatly appreciated!

-Dan

We don't have, and never have had, specifications (meaning we can trace them to national standards, verify them in the field, and warrant the performance) for mixer measurements. One key reason is that the particular behavior the mixer greatly effects the uncertainty (for example reconversion on the LO port of IF and RF signals, bouncing off the LO source) so if one wanted to be very correct, the number of things you must know get's very large.

If you want a reasonable estimate of uncertainty, it is the error in the power meter at the input frequencies (maybe 0.15 dB), plus the error in the power meter at the output frequencies (another 015 dB), plus S21 error transferrring the power measurement from input to the output (careful cal keeps this to 0.03 dB), plus the input resisudual mismatch error (depends upon the mixer S11 and source match) plus the mixer residual output match error (S22 of the mixer and load match). But since there are a lot of them, you can RSS the errors; to be more correct, you can estimate the Sdev of the errs, RSS them, and multiply by 2.77 to acheive a 95% confidence interval.

That's all for amplitude.

For phase you have exclude the power meter errors, use the 6.6 times the amplitude errors fro the match terms and S21 cal terms, and then add back in an error estimate for the phase-reference calibration. Our description of phase accuracy is quite large (+-6.5 deg over best region), but my estimated uncertainty is less than 1 degree, and my experience in determining error w.r.t. group delay computations, I think it is on the order about 50-100 psec.

And our phase spec is absolute, but really most cases you only care about relative phase error, and I think it is on the order of 0.25 deg from comb to comb tooth.

So, let me konw if you need more info on estimating your uncertainty.