dbi unit

hi everyone,
I would like to know which unit is correct when we calculate antenna gain in HFSS, dBi or dBd?
thanks in advance!

Hi

They are both correct, depending on what you compare with.
dBi is compared to an isotropic antenna(fictive), while dBd is compared to a dipole.

dBd = (your antenna) dB - (dipole antenna) 2.15 dBi

Regards

@tyassin:
Thank you for your kind attention.
In a more specific case, when I create a 3D view Gain report like following image.
(Quantity - Total gain; Function: dB)
Simulation result shows a value at 1.9. Does it mean that is the antenna absolute gain? If it's true, how much it is in dBi?

Thanks again!

You are mixing two questions. Gain can be referenced to an isotrope or a dipole. That is the dBi vs dBd stuff. The "different" types of gains in the HFSS post processor also include a reference to a particular polarization (as well). Think of the difference between a circularly polarized omni antenna and a linearly polarized antenna for example.

Go read the details of the definitions (on line help) and look up the references Ansoft cites to get your hands around the differences. Stutzman has a useful book on the subject as well.

@azulykit:
Thanks for your helpful suggestions