simulating 2 ports RFID tag antenna using CST

Helloo.. i really need your help.. i have to simulate a crossed dipole RFID tag antenna.. both of the antennas are independent to each other.. So after I simulated the tag antenna, I got 2 antenna input impedances and both of the impedances are quite similar to each other.. In order to calculate the tag reading range, I need to insert the antenna impedance and the other values alos like antenna gain, etc. My question is, which antenna input impedance should I take? Should I take the average value of those two impedances? Or should I combine those two impedances? Please anyone help me

kindly post your simulation in order for us to help

thanxxx so much flashking for your reply.. here I attach my antenna design.. before this I calculted the average of the antenna impedance for both ports, and then I inserted the values in the reading range equation.. but the result is not the same as in the data sheet.. together with the design, i also attach my results and the data sheet result.. relly hope that you can help me solve this problem..

The purpose of your simulation isn't clear. To take advantage from the cross dipole, it's normally operated with a 90° phase shift network, generating circular polarized waves. If this is the intended operation mode of your antenna, it should be tested with the phase shift network, isn't it?
Averaging input impedances sounds as reasonable as averaging apples and oranges...

Hi FvM.. yes the purpose of my simulation is to create a circularly polarized antenna, so that I can get an omnidirectoinal radiation pattern.. Can you please explain to me how can I test with the phase shift network? Is there any tools provided in CST Studio suite for this phase shift network? Please guide me..

Ideally, a 90° hybrid would be used.

I'm not sure if this works, but can you setup two lumped ports with one connection in common, e.g. port1: x1---x0 and port2: x2---x0 and then tell CST that the two ports should have a phase shift of 90°?

Hi flanello... I don't think it will work because both of the ports should be independent to each other.. huhuhu.. i totally dont have any idea what to do with both of these antenna impedances.. I dont know how to calculate the reading range aith those antenna impedances.. huhuhu

If the ports should have a 90° phase shift, they aren't independent.
Have you tried the simulation?
And if you want to use this antenna you need either an RFID chip that has a three port interface, or you need to connect a phase shift network between the antenna and the RFID chip.

Hi flanello.. I have tried to simulate the antenna design (UPM Frog 3D).. But I got 2 antenna impedances.. I am bit confused, which antenna impedances should I take in order to calculate the tag reading range .. UPM Frog 3D use Monza 4 tag chip, which have four terminals.. Do you have any idea?

Can you look into the data sheet of the the antenna or the tag chip for an impedance value and compare it with your results?

Hi flanello.. In the data sheet, the chip impedance at 866MHz is 13-j150 [ohm]. The antenna impedance from my simulation at 866 MHz are 1.32+j157 [ohm] and 1.34+j156.8 [ohm]. Both of the antenna impedances are quite similar to each other. Compared to the chip impedance, the resistance of the antenna is very much smaller than the resistance from the chip impedance. But the reactance for antenna and the chip is not much different.

I've been working in UHF RFID for a period of time,and doing the same work as nmohdfau.
I can not open your attachment for i used HFSS, but i think your tag antenna design is not circular polarization because it's too hard to implement on TAG. So the dependent antennas are just the same and construct two linear polarization.
The impedance of 1.32+j157 [ohm] and 1.34+j156.8 [ohm] are too small in Rx .

@waw: Please open a new Thread for a new question.