Radiation efficiency and Antenna Gain question.

An antenna radiates its energy by power dissipation and heat dissipation. How can you tell if your antenna is dissipating heat energy in HFSS? The antenna I'm simulating is matched, -20dB, so I think it should be radiating by power dissipation. I looked at the far field radiation plot and the gain is low, -40dB.

That is very simple, simulate the materials but without adding the loss tangent and check your return loss. If the return loss is still low then your antenna is radiating,

I already said that the antenna is matched, S11 <= -20 dB. That is what you mean for return loss, right?

I would like to know why a matched antenna would radiate poorly. The only answer I can come up with is heat dissipation.

Does anyone know?

There are several sources of heat loss in an antenna. One is the ohmic resistance of the metal parts. Another is the losses in the surrounding material.

In the HF and lower range, vertical antennas over earth have a high amount of loss in the earth.

Can HFSS tell you how much surrounding materials like a ground plance affect the return loss?