Rfid tag antenna help

[Enrique Romo]

Hellow Guys,
I am new to HFSS and I am trying to duplicate the results of an RFID tag antenna working in the 915 MHz. I don't know how to conjugate match the antenna with the chip. Also, I am using a Alien Highs chip (Impedance 27.4-200j ohm) and I don't know how to set it up in the antenna design in HFSS, should I use a lumped port or what??? I need HELP!!!

 

[E Kafeman]

HFSS is a good simulation tool but not of much use when last few dB's must be found for the real hardware.

Conjugate matching for a single frequency with ideal components is simple: https://home.sandiego.edu/~ekim/e194rfs01/jwmatcher/matcher2.html
This tool is ok for a simulation study but for a real hardware that should be impedance optimized is it a rather useless tool as assumes ideal components and do not care about PCB losses.
It can cost several dB's in increased transmission loss due to misleading calculations.

For better matching result must somewhat wider frequency band matching be done, using measured S-parameters for antenna as well as S-parameters for the real matching components.
If possible should measured/recommended impedance values for same frequency range also be used for the radio.
Making it further a bit more complicated, if antenna environment not is fixed such as due to free space relative handheld, will its impedance change.
Calculate optimized matching network including these different scenarios is automatically done by AnTune software.
Either is AnTune feed with measured S-parameters or can it read live values directly from a VNA and present optimized values, real E12 values and component-type, article number and schema.
Almost no delay, result will update 10 times/s if input parameters are changed, live or by manual manipulation, which makes it real simple to modify antenna and filters for best performance directly a lab-bench.
Optenni can be an alternative to AnTune but downloadable version is not fully functional.

 

[flanello]

You can use a lumped port.
If your chip has an impedance of (27.4j200) ohm your antenna must have an impedance of (27.4+j200) ohm for conjugate matching.

 

[Enrique Romo]

Thank you flanello,
So, in the lumped port I input the resistance and the capacitance which will give me 27.4-200j ohm but how I set up the antenna impedance to 27.4+200j?

 

[flanello]

I would not use the capacitance section of the port. If you use it you need carefully check if its working as you expect.
You can get the impedance of the antenna with the result Z(Lumped Port). You have to design/modify the antenna so it has the impedance that you want.