Hi,
I am trying to measure the parameters of an external differential antenna I designed. I have been using the application note AN4974 in order to figure out how I can measure these parameters and I have some confusion on the setup and the results I am receiving so far.
I've looked at other posts and the way I understand it is that I should connect my VNA in single-ended mode (ant1 connected to signal and ant2 connected to the shielding/body of my SMA connector). Is this correct?
I have taken a measurement of a flexi antenna I would like tuned and I also tried to measure the antenna of the st25r3911b-disco board to verify if I measured the flexi correctly. My issue is that the measurements both look completely different from what I see on the application note. Using other posts as a reference, my antenna looks somewhat similar. although, my values are strange compared to others and the app. note.
The first picture is my flexi antenna and the second is the antenna of the st25r3911b-disco board.
First of all, the low frequencies are very jagged and I'm not sure why. My only guess is maybe there's something wrong with my calibration process. I'm also guessing this may be why I'm measuring negative ohms... The antenna inductance looks okay for both cases. I expected my antenna's inductance to be high. My other confusion is that the inductance at the resonant frequency is very high compared to the app. note and other references.
Am I understanding the procedure for measuring correctly? Is it just the calibration of my VNA?
Any help or pointers would be appreciated.
Thank you,
Kaitlyn
