Ideal dipole antenna close to metal ground plane

[kuanfu]

ideal dipole antenna

Hi,everyone

I am using HFSS to simulate dipole antenna near metal ground plane. the dipole is parallel to the metal ground plane.

when i simulate this dipole antenna for 2.4Ghz centre frequence and place it very close to ground plane 1mm to be exact i get badly matched dipole shown by s parameter.

however when i check the farfield pattern at 2.4 ghz,the gain is around 9dbi and its giving smooth and wide main lobe with maximum in Theta=0 degree.

can anyone explain this why this is happening because in my view if antenna's s parameter is not good it should not radiate and its gain should be very low.
any help would be highly appreciated.
thanks

Kuanfu

 

[cuongtran]

dipole ground plane

But we see that your center frequen is at 2.5G?

 

[jallem]

2.4ghz antenna in presence of metal

HFSS has two gains,
gain and real gain. Gain
is based on the energy that radiates
by the antenna while real gain is based on
the energy supplied to the antenna, or
in other words includes the "losses" due
to reflection or low S11. Try to plot
realized gain to see if you get any difference.

 

[shahid78]

dipole antenna ground plane

yes i agree with jallem.

the gain you are talking about is the gain which doesnt take into account the losses due to mismatch. so even though ur S11 is very poor but but as your antenna is directive so whatever power gets to it it will be radiated efficiently and you will get high gain

on the other hand realized gain takes into account the reflection losses so a large part of power is reflected due to poor matching and only part of the input power will be radiated by the antennas as compared to the input power and surely u will get low value of realized gain

so as mentioned by jallem if you plot the realized gain and see how much you get , it will confirm our point

regards

 

[cuongtran]

ground plane dipole

Hi Shahid, you mention to plot "realized gain"; so please tell me how to plot this in HFSS, thanks, I need to verify also, thanks.

 

[a&f_hfss]

realized gain s11

hi, kuanfu

you can choose 'realized gain' when you plot

 

[cuongtran]

ideal dipole gain

Hi, with hfss for plotting, two results (real and effectiv) are the same!