What should be the port impedance for RFID tag antenna in IE3D?

[nmobin27]

Hello everyone

Would you please tell me what should be the port impedance for simulation of RFID tag antenna in IE3D? I want to use Alien Higgs 3 IC which has the impedance of 12-j140. For conjugate matching, do I need to set the port impedance 12+j140? Which matching technique is preferable? For example, T-matching or stub matching. I appreciate your quick reply.

 

[WimRFP]

If you are just running antenna simulation (with Smith Chart curves as result), just design your antenna for the impedance that the chip wants to see. So you need to design an antenna that has an input impedance of 12+j140 at the design frequency. You may know that you can select "impedance" during Smith Chart view. You can't specify a complex impedance for plotting the Smith Chart.

If you want that 12+j140 is in the center of the chart (not recommended), You need to add -j140 Ohms in series with your port and set Zc = 12 Ohms. You can set the reference impedance for the Smith Chart after the simulation (I though "terminating impedance").

There are two ways to make the series capacitance: via a second port and using the spice simulator, or by modelling a series capacitor. With the spice simulator you can connect a lumped compent to the additional port.

When the relatieve frequency range is small, you can draw/model the capacitor in IE3D. I frequently used this option. As long as you make sure the plates allign with each other and are meshed the same way (so all segments are alligned), you get good results.

Just to make sure, I would simulate the capacitor seperately.

The port impedance itself you can just leave at 50 Ohms. If you Change the reference impedance for Smith Chart plotting, the simulator may show normalized impedances instead of real impedance.