Antenna Matching Tool not giving accurate values?

[MZilv.1]

I am new to antenna matching so I decided to use the ST25R Antenna Matching tool V3.1. It seems simple enough, and gave me this output after adding in my antenna parameters (taken right from the datasheet):  

However when I simulate this circuit in Qucs, the outputs don't seem like the parameters calculated actually matched the antenna:

 

I was under the impression that the circuit should be matched in a way so that the target frequency is in a valley of the S11 plot and a peak of the S21 plot. If that's true, is there a parameter or value I'm not setting correctly or do I just need to do the rest by hand?

[Travis Palmer · Accepted solution]

Hi Matt,

AN5592 provides some information about the calculation of the matching values. Unfortunately the calculation of Cs and Cp is only an approximation.

Also the QUCS simulation template inherits some more components (parasitics) to be closer to the real system.

We are currently working to make those calculation more precise.

Meanwhile please use the chapter 6.3 of AN5276 to finetune your simulation and real system.

br Travis