Near field antenna tuning without a Vector Network Analyser (VNA)
0xFRED’s blog post is about the making of a capacitive touch pad on a PCB.
This one will be a front door entry system, so I decided to go with something that could read my NFC implant but also had a numeric keypad for the kids (and anyone else) to use. Not everyone wants to be chipped. Crazy, isn’t it? I’ll write more up on the board when it gets closer to completion, but for this post I’m going to concentrate on a small PCB antenna that’s intended for use with a tiny implanted tag.
I must admit the range and sensitivity wasn’t great. I had calculated that the PCB antenna should have an inductance of about 1μH so I just used the same matching components that worked well previously. What I really needed to tune the matching circuit was a Vector Network Analyser (VNA). Unfortunately these are very expensive and I’d likely only ever use one for this. Is there another way? Well, luckily I came across an article entitled “Impedance matching for 13.56 MHz NFC antennas without VNA”
So with some measurements and calculations, the impedance was matched for the frequency and the circuit worked!
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