S11 parameter measurement in NFC antenna design

[leonardorafaeli]

Hi,

I'm designing a NFC antenna for my PN5180 PCD.

I'm doing this based on "AN11740 PN5180 Antenna design guide".

My question is about "4.2.1.6 Assembly and measurement " level.

Is this step( impedance measurement between TX1 and TX2 pins) done in live mode ?

I mean is it necessary to power on the PN5180 during the measurement or it must be powered off ?

[leonardorafaeli]

There is Problem with my measurement, In both measurements(Initial Coil measurement and TX1/TX2 measurement) my parameters was not stable,It changes and also my smith diagram is a bit different with document.I used same ZVB20 VNA and it was well calibrated. Does any one have any suggestion whats problem and how could I fix it ?

I attached my first measurement smith chart( from antenna coil leads) During measurement values changes from 3~11 ohm in real part.

[leonardorafaeli]

Dear Xia & Extephania,

Thank for Your replies.

I watched NXP NFC Antenna design webinars.

My question is if PN5180 must be powered off during impedance measurement between TX1 and TX2 pins, then why we does not de-solder the inductor L1,L2 which removes, PN5180 output pins effect on our measurement ?

This disconnect antenna circuit from  from TX1 and TX2 pins which could change S11 parameter of antenna circuit.

[onlineit]

The  impedance measurement between TX1 and TX2 pins should include PN5180 and it must be powered off.

[onlineit]

it must be powered off.

[estephania_mart]

Hello, 

Maybe to help you understand better this topic, you can check the available webinars in the antenna design topic.

There are 6 of them and those might be good guidance on the topic. 

Regards, 

Estephania