Both PNA and ENA has this features, the fixture simulator.

i am abit confuse with the purpose of 50ohm to 75ohm adapter, is it needed because of physical connection compatibility, or because we need convert 75ohm to 50ohm then only measure, if we need convert them to suit 50ohm system , then do we still need to change to 75ohm using port impedance conversion feature as we have convert physically to 50ohm form 75ohm.

and also, when we want to measure 75ohm, or 100 ohm, assuming there is no physical connection compatibility issue and they can connect directly to the NA , we change the port impedance using impedance conversion to 75ohm or 100ohm, but calibrate using 50ohm kit, is this correct method to do so?

thanks for anyone help.

i am abit confuse with the purpose of 50ohm to 75ohm adapter, is it needed because of physical connection compatibility, or because we need convert 75ohm to 50ohm then only measure, if we need convert them to suit 50ohm system , then do we still need to change to 75ohm using port impedance conversion feature as we have convert physically to 50ohm form 75ohm.

and also, when we want to measure 75ohm, or 100 ohm, assuming there is no physical connection compatibility issue and they can connect directly to the NA , we change the port impedance using impedance conversion to 75ohm or 100ohm, but calibrate using 50ohm kit, is this correct method to do so?

thanks for anyone help.

If you can physically connect to the 50 ohm port (that is, if the connections mate and make contact, such as a PC board fixture or probe), then you may calibrate in 50 ohms, connect a different Z device and use the software feature under fixturing to mathematically transform the S-parameter results to what are in referenced in new Z impedance.

For type N, they sort-of connect; if you put a 75 ohm male on a 50 ohm port, the center pin is smaller and most of the time it won't make contact. If you put a 75 ohm female on a 50 ohm male, the female center pin will be over-expanded and sometime break off a finger or two.

If you use a connector that has 50 on one end and 75 on the other, then you must calibrate in 75 ohms using 75 ohm standards. In this case the raw match is still 50 ohms, much like the first case above, but the calibration standards are 75 ohms so there is no need to do the mathematical transformatin.

There is also a minimum loss pad that changes the port impedance to 75 ohms, but has loss, so you must still calibrate after the pad or the insertion loss and return loss will be in by 2 times the pad loss.

If you are in a different impedance, one for which you don't have a cal kit, like 100 ohms on PC board, then your only option is to calibrate in one impedance, like 50 ohms, and do the mathematical transformation.

Your next question, undoubtably, is "which way is best". My unsatisfactory answer is "it depends".

If your system is very stable, and your cal kits are not that good, then using a minimum loss pad is best. If your system (directivity in particular) is not very stable, then doing a calibration without pads can be better. If your cal kit is very poor, then using a calkit in an impedance that is better and mathematically transforming will give a better result.