This basic method will outperform a 'typical' VNA SOLT calibration (i.e. SOLT without the attenuators) for a simple thru loss measurement especially for measuring very low insertion loss at microwave frequencies using fairly long cables.
I do not agree. The attentuator method is useful work around for simple scalar network analyzers that can not be calibrated.
For vector network analyzers, calibration with a good cal kit is the most accurate method.
Put yourself in the shoes of the analyser.
I come from the Bochum University measurement group that has invented many of the modern calibration methods as implemented in R&S or Agilent VNA, so I have a certain bias towards calibration rather than pure hardware approach.
Of course, you can break calibration if you combine long bad cables with few sweep points, and maybe add some user error. Yes, you can break it.
But your solution with the attentuators has some major weaknesses, too. It suffers from the unknown return loss of the attenuator (how good is that?) and will decrease the SNR and dynamic range of the instrument by 20 or 40dB. The increased noise in the sampled signal will increase the measurement error.
Finally, if you insist to use an attentuator, you can always combine your attentuator method with a proper SOLT calibration. That will be more precise than attenuators with simple THRU normalization.
The increased noise in the sampled signal will increase the measurement error.
That's my point. I've seen so many engineers get errors on a SOLT using the default analyser sweep settings on meaurements at several GHz using long cables.Of course, you can break calibration if you combine long bad cables with few sweep points, and maybe add some user error. Yes, you can break it.
As long as the attenuators have >30dB return loss then I would still argue that simpler is better. The measurement error with >30dB return loss is so small then I'd argue that the error introduced from the physical act of SOLT (rather than theory) will present a risk of making the measurement worse. But I doubt you would be able to 'see' the error or know it was an errorFinally, if you insist to use an attentuator, you can always combine your attentuator method with a proper SOLT calibration. That will be more precise than attenuators with simple THRU normalization.
But the attenuator return loss can be checked and measured with good confidence on the VNA.
Also note:
If I preset the Agilent 8753ES by my desk it defaults to 201 sweep points. If I get time I'll make some measurements comparing 1metre cables on a default SOLT using an 85033E cal kit against a thru loss using some nice 18GHz attenuators on something like a filter or switch.
How? You have described that you do not trust calibration, so you start with an un-calibrated inaccurate VNA. To measure the return loss of your attenuator, you must first calibrate your VNA. How to calibrate that, if you have no reference that you can trust? If you just use another attenuator as the reference, your results might look nice, but all the impedance error from the attenuator is now in your data.
In SOLT, the standards are very well defined and measured against trusted standards. With your attenuator method, you have no trusted reference to start with.
I have described the real world limits of trying to calibrate to compensate for a very long (imperfect) cable at microwave frequencies.You have described that you do not trust calibration
Do you see the difference?
Yes, I see your point.
Maybe we can agree that your method of improving return loss in hardware, and more advanced calibration methods that can remove imperfections of the hardware, can be combined.
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