RF measurement using VNA

[wireless101]

What is the best way to connect an RF pad to a vector network analyser.
I have SMA connector on one end(port) but on the other end(port), I have just RF pad. How can I connect it to VNA to get best estimation of S21.

 

[pragash]

you cant connect RF pad directly to VNA. you need to connect/solder a connector/cable eg. SMA or SMA/UFL cable soldered onto the pad.

 

[wireless101]

Thanks Pragash. Soldering a UFL connector is good idea but it also introduces loss in the system. Do you have any suggestion for a connector that would not introduce any loss in the system.
On my PCB I have ground-signal-ground RF pads on one side while I have SMA connector mounted on other side. Basically, I want to estimate path loss from the SMA connector (on one side) to RF pad signal(on other side).
How can I measure this with VNA, without soldering anything on the RF pad.

 

[Romansh]

There is no way to measure S21 of a system (unless it is just a transmission line or attenuation pad) without connecting both ports. Any connector will add some loss. You can de-embed this loss using ADS or other RF simulator.

 

[wireless101]

Actually, as I described in previous post, its just a transmission line.

 

[wireless101]

Is it possible to estimate S21 for transmission line by knowing just S11.
Is S21 half of S11, when the transmission line is open on the other end.

 

[pragash]

you will need some sort of connector at the end to connect to network analyzer and that will induce losses. the only way is do TRL calibration to subtract the losses from the system so you will only measure the TL line.

 

[bg8npk]

soldering a cable to VNA is a good way to measurement. the cable caused lose can be delete by calibration or input the cable parameter in VNA. if the pad is one element of your network, you can connect full network to you VNA and use the TDR function to locate the reflected element.

 

[FvM]

The best solution is to make a calibration adapter (single port SOL or dual port SOLT, depending on the intended measurement) with the same interface as the device under test, can be e.g. UFL connector or probe needles. Calibrate the VNA with this adapter to get rid of cable and connector losses and reflections.

There are standard pad geometries for test structures used with impedance controlled PCB manufacturing. They are mainly used with TDR measurements but could be used with VNA as well.