HFSS - Strange results for Monopole Antenna Parameters

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EMHerb

Newbie level 5
Hi,

I ran some simulations in HFSS for a monopole, using a lumped port.

Port impedance is set to the complex conjugate of the antenna's impedance. The results obtained shows a well-matched port, where S11 is close to -60 dB.

But when I compute the antenna parameters with an infinte sphere under "Radiation tab", the results are:

1) Peak Gain = 0.68226
2) Peak Realised gain = 1.08 e-05
3) Radiated Power = 0.00387 W
4) Accepted Power = 0.00396 W
5) Incident Power = 250.99 W

Questions:
-I find it strange that incident power is 250.99 W. I thought the manual said that lumped ports are 1 W?
-If my S11 is well-matched (-60 dB), why is my peak realised gain not close to my peak gain? And why is accepted power so low?

roxxon

Member level 2
Maybe a bit late, but I think I can give an answer to the first question: as I found out with several simulations, just the real part of the power (the real power) into the port is normalized to 1W, but the incident power appears to be the total power (apparent power) and is therefore 1W *sqrt(Re(Z)^2+Im(Z)^2)/Re(Z).

But as to why the accepted power is so low... I don't know. I got similar results and am still trying to find solutions to those effects.

waw

waw

Points: 2

TheArcane

Newbie level 5
Hi,

Just a thought, HFSS computes the antenna parameters at the solution frequency by default. Make sure you solve at the correct resonant frequency and then compute the parameters. I don't recall now, but maybe if you do a fast sweep and tell it to save all the fields, you can also calculate the parameters at different frequencies.

Hope that helps.

flanello

Hi,
are you using a wave port or a lumped port?
I have the same effect here using a lumped port. Perhaps with a lumped port it will work.
In another post () I have found this formula:

incident power (Pinc) = 1W
accepted power (Pacc) = Pinc * (1 - s11^2 ) (ie mismatched loss)

But this doesnt' work for me.

Are you using a complex port impedance?
I think the above froumla works if the port has only a resistance and no reactance.

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