as a beginner, I know S11 parameter is measured to know the resonance frequency of the antenna, But when I measured S11 for the Ti's "TIDA-00524" board, I didn't get the resonance frequency at 13.56Mhz instead, I got resonance at 13.56Mhz when i measured S12/S21. Would you please help me in tuning the external antenna and why the S11 isn't showning 13.56 MHz for this already tuned board?
I have attached the S11, S12 measurement and my setup for S12 measurement.
