negative db gain

Hi,

I am getting negative gain in result of a simulation in HFSS so please kindly guide what does negative gain means?

negative gain means, you have positive gain outside the boundries. Depends on your structure try to find another vawe port.

Negative gain can indicate that you have an antenna with significant insertion loss. Think of a dipole with an attenuator in series. This is not normally a good thing.

Or you may have done something wrong in the simulation.

I have the same problem too, especially the directivity? how can a directivity have negative value? Which is impossible in theory. Please can anyone explain it to me?

A negative gain antenna can be used to bend air. It is very powerful. The trick is to actually build it without losing all of its "negativity".