All,
The IFA described in in AN043 was analyzed with Sonnet Lite EM software. This SW is provided free of charge from Sonnet.
A 3D view of the IFA analyzed is shown below:
The predicted S11 response is next. The best S11 was at 2.2 GHz rather than the desired 2.45 GHz. This could be due to many factors such as the exact location of the shunt trace ground via, Sonnet box size, cover distances, thickness of air layers above and below PCB (FR4) layer, etc. I'm not certain exactly how the EM simulation shown in AN043 was setup.
Sonnet generates S-parameter data after the simulation is complete and saves to a file if desired. The predicted S-parameter data can easily be matched at 2.45 GHz with lumped components. Sonnet provides a text editor so ideal components can be simulated along with the predicted S-parameter data. Below I show the schematic simulated in Sonnet. I used Agilent ADS to show the schematic view for clarity. Notice I added a series 1.2 pF cap and a shunt 0.4 pF from the 50 ohm point. The "S1P" data box uses the EM generated S-parameter data. A better simulation would include ESL and ESR for the caps.
The new S11 plot (antenna matching network + EM simulated IFA) is shown below. Notice the best S11 dip is now at 2.45 GHz.
I was not able to attach the Sonnet EM (*.son) file. Contact me via email if the file is desired or there are any other questions. Thanks to Jim Merrill at Sonnet SW for his technical support.
Regards,
Eric Hooker
RF Consulting Engineer