Hello! I've matched a couple antennas before using the same methodology. In this particular instance, I am not able to get where I need to and am turning to people with more experience (you!) for some insight. Trying to tune a PCB antenna to 915 MHz. Pi filter footprints are in place.
A semi-rigid cable is attached at a 50 ohm point (just after a balun), just before the pi filter to the antenna, so:
IC -> balun -> 50ohm point (sma cable here) -> pi filter -> antenna
This image shows the calibrated VNA with a 0 ohm resistor in the series position of the pi filter:
OK, so from that, replacing the 0 ohm resistor for a ~5pF capacitor should bring the impedance down along the constant resistance circle to here, or just about, right?
Here's what I get instead:
As stated, in the past, I got results (mostly with inductors) that matched theory more closely. In this case, not too sure why I'm observing this, and what to do next.