radome thickness

Hi Everybody!

I have to simulate the behavior of an antenna (a simple dipole) surrounded by a radome.

I have to plot the gain at different thickness of the radome.

I have notice that if I plot the rE (db) (the power of the E field) I obtain the maximum value with the antenna with no radome, and it decreases as the thickness of the radome increase.

But if I plot the gain the behaviour is not the same.
Shouldn't I obtain a similar behaviour, obvioulsy with different values?

Because the gain, from definition, is normalized by the gain of an isotropic antenna and that shoul be fixed, isn't it?

Thanks for your help.

It depends on whether your radome is lossy or not. From the HFSS, the real gain contains the loss from the impedance mismatching and loss from the dielectric materials and conductive loss, so that might be a more "real-world" parameter you want to know. In contrast, the gain in HFSS does not include the impedance mismatch, so if the radome is lossless, maybe the gain will not decrease when you increase the radome thickness.

First of all thanks for your answer.

So you suggest me to plot the "RealizedGain" (I suppose is that the one you call real gain..) and not the "Gain" from HFSS to obtain a more real-world result and to consider more completely the problem?

My radome has a small loss tangent, but is not lossy (0.0005)

In my problem I have to increase the thickness of the radome and , fixed the thickness, change the parameters of the material (loss tangent,dielectric constant ecc..) so probably the realized gain is the best solution.

Obviously if I simulate the antenna without radome the "gain" and the "realized gain" should coincide, isn't it?

Thanks again for your help!

Hi. Yes, what I means real gain is the "realized gain".

Generally speaking, the "realized gain" include the impedance mismatch for the gain calculation. For example, if the S11 (return loss) for your antenna is -10dB, which means that 10% of the power are reflected back to the source. So the input power for the antenna is only 90%. If your antenna (+radome) conductive loss and dielectric loss is 90%, which means that 90% of the input power is radiated out, then you will get this relationship:

"gain"=0.9*"directivity";
"realized gain"=0.9*"gain"

So in general case: directivity>gain>realized gain in HFSS.

The same thing applies to IE3D "antenna efficiency" and "radiation efficiency"....

Good luck