# Where to connect the VNA during matching network tuning

I'm trying to design the matching network between an antenna and its transmitter, running at 868MHz, as shown below. There's probably about 20mm between the transmitter output and the Pi network.

When connecting the VNA to the PCB in order to measure the impedance, where should the VNA be connected? At the transmitter end, or at the start of the Pi network?

My understanding was that in order for the VNA to "see" the load how the transmitter sees it, the VNA should ideally be connected close to the output of the transmitter (in my case, I have a blank PCB, so I've soldered a UFL connector directly on the transmitter output pad). However, after reading this article by Tektronix, it states the following:

it’s important to keep in mind that the impedance to be matched must be measured at the point where the matching network will be placed.

I understood this to mean that I should solder the UFL connector close to C13 in the image above (and possible cut the trace between the transmitter and the UFL connector).

• how do you propose connecting at start of PI network? If your using sufficient bandwidth, you can connect at the pcb end and time-gate out the board launch as well as the device on the other end Mar 26 '19 at 1:49
• @johnnymopo - I've edited my question to add further clarification. You mentioned the following: you can connect at the pcb end and time-gate out the board launch as well as the device on the other end. Can you explain what you mean by this? Mar 26 '19 at 5:38
• @johnnymopo Yes, could you please explain that? :) Nov 5 '20 at 15:12
• look up VNA de-embedding - essentially using the time-domain transform on the VNA you can "gate" the time-response to de-embed to your DUT Nov 16 '20 at 22:15
• @johnnymopo Wow, it's really not very helpful to just say look up VNA de-embedding so smugly and tersely when you yourself have already given an, in fact, really nice answer to this elsewhere a whole year before this question came up. I'm torn: I'm both grateful for the answer you gave there and slightly mad that you didn't deign to link to it... An odd one. Nov 19 '20 at 22:53