Author Topic: VNA Compact Cal Kit from Rosenberger  (Read 999 times)

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Online dcarr

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Re: VNA Compact Cal Kit from Rosenberger
« Reply #25 on: May 16, 2019, 07:17:50 am »
Great point about the connector repeatability.  I can recommend Rosenberg 32K243-40ML5 as a high performance yet moderately priced option.  It clamps on to the edge of the board and if you bend down the center PCB contact slightly, it acts like one of the expensive Southwest Microwave connectors.  (ie: You clamp it on to the PCB in one place and then when finished you can unclamp it and move it to a new location.)

« Last Edit: May 16, 2019, 07:56:00 am by dcarr »

Offline TheUnnamedNewbie

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Re: VNA Compact Cal Kit from Rosenberger
« Reply #26 on: May 16, 2019, 05:18:50 pm »
Could you care to explain/clarify? The best accuracy should be achieved when the error on the calkit with respect to the stored values used in the VNA are lowest, shouldn't they? The advantage of an ideal connector in a calkit is because an ideal connector means you need less precise compensation values to cancel out the non-ideal connector. After all, that is why sliding-loads are a thing - they wouldn't work with near-perfect connectors.

The point was that when you are measuring the DUT you are going through its non-ideal connectors, which for example may have a nominal characteristic impedance different from 50 ohms due to physical design. No matter how good your cal kit is, this error gets added to the measurement, and conversely if you construct a cal kit out of a connector that closely resembles the DUT's connectors, the error of the connector gets calibrated out.

If you want to measure only the DUT on a test-board, you need to calibrate on the test board with TRL (ideally even TRLL). I don't know about the math and I never do this, since I tend to either use GSG probes or waveguide stuff, but I have once been told that you can get better performance if you first calibrate up to the ports of your expensive VNA cables, then calibrate the TRL, instead of going straight for the TRL (this can also give you an idea about the repeatability of the TRL, since you can see the difference between connectors if you look at the time-domain).

In the spirit of OwO’s comment— if you really want to characterize a PCB mounted device, you should be using on board TRL or similar fixtures.  These will calibrate out your connectors, PCB transitions, and your transmission line geometry.  Best of all, it’s cheap!  You don’t necessarily have to have a traditional cal kit to do it.

Well this is true if you use <10$ SMA edge launch connectors which will vary by quiet a bit but is pretty cheap. And arguably this precision is all you need for most application which use SMA edge launch connectors in the real product anyway. However, if you want to get rid of connector variations, they won't do. Have a look at the 3.5mm/2.92mm edge launch connector prices! And you will need 6+ for the TRL kit (depending on frequency range) and 2 for each DUT!

The thing is that you want your connectors to be as ideal as possible. After all, any variability in the connectors (both between different connectors and the repeatability of the connector itself) will translate into larger errors and uncertainty on the device performance. Just because it will be used with cheap connectors does not mean it is okay to measure it with cheap connectors - you want as precise measurement as possible, since errors tend to compound in simulations and when you start cascading things. And while you might not get big amplitude variations, phase variations can be very important - after all, you need to 'un-rotate' the transmission lines you use.

OP, getting a through that can match the performance of that rosenberger kit might not be as straight-forwards as you think. 3.5mm air-dielectric through are not exactly cheap.
I didn't see any indication on the 3.5mm(f) MSOT (03K30R-MSOTS3) data sheet that the "Through" is an airline. 
It looks like both use the same short/open/load on the data sheet.

To be a APC3.5 mm connector that adheres to the standard, it has to be a airline connector. There is no such thing as a non-airline APC3.5 mm connector.
« Last Edit: May 16, 2019, 06:24:41 pm by TheUnnamedNewbie »
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