FEKO and input impedance - subtract loading?

[Zangetsu57]

Hello everyone,

I'm a bit stumped when using FEKO. I'd like to obtain the input impedance of an antenna, which I estimate to be approximatley 200-300 ohms (folded dipole). In POSTFEKO, there is an option to "subtract loading" above the reference impedance. As far as I can tell, this needs to be checked in order to obtain the correct input impedance. Am I correct?

I somewhat checked my answer by looking at S11. To see how well the antenna matches to a 200 ohm transmission line (S11 magnitude), I've been checking the box "subtract loading", and a reference impedance of 200 ohms. This result matches the graph obtained when hitting the "s-parameters" button, assuming a reference impedance Z0 of 200 ohms in CADFEKO.

Any info would be great. Thanks!

 

[e_m_c]

Usually such feature is used to subtract external load you applied at antenna port. Like if for the excitation you have been using [1 V Voltage Source + 50 OHm] then your observed impedance will contain these 50 ohms as well. So, to get impedance of the antebnna itself this one needs to be subtracted. If you apply just Voltage Source without the load you need to have 'subtract' option swithced off.