We test the waveform at feedpoint of antenna. And find the frequency of the waveform jump up and down. It is much lower than 13.56MHz. What kind of problem for this,software or antenna matching? We use a android main board connecting to NFC board,and the main board can find NFC boad.
you can check the following link
there is an antenna tool where you can check your matching values and some application notes that can help you.