PEC for sure? Does that make sense?
Yes, you are right. One draws the airbox with PEC on the outside, but I think HFSS "inserts" a radiation boundary there. So whilst it looks like PEC, in fact it is not.
If you give the frequency and dimensions of your antenna, and the dimension and dielectric properties of the dielectric, I can see what I get from "my" 3D solver (Empire XCcell).
Code:
Er = 81, bulk conductivity = 0 (i.e. perfect insulator), relative permeability=1.0
length of dipole = 1.28 m
radius of dipole = 2 mm
feed gap for dipole = 2 mm
dielectric radius = 587 mm
dielectric length = 2.56 m
frequency 14.0 MHz
The length of the dipole is not quite right for 14.3 MHz, as a quick calculation will show, but I originally based this on a wavelength of 20 m. But try those dimensions, but I know resonance will be a bit below 14 MHz. The value I got for the resonate frequency looked quite reasonable.
If you get anywhere with a reasonable input Z, I'd be interested what happens with distilled water, which according to the material properties in HFSS are:
Er = 81, relative permeability=0.999991, bulk conductivity 0.0002 Siemens/m
These are the results I get:
Code:
Peak directivity 1.4228 (not dB)
Peak gain 1.4192 (not dB)
Peak realized gain (includes mismatch loss) 0.0043741
Radiation efficiency (0.99748) - i.e. over 99%.
At first I thought the peak gain was too high - I expected a large reflection at the air/water boundary. But whilst that is no doubt true, the reflected power will just be be reflected into the dielectric, and some more escape. So it all the power will be radiated, so the efficiency should be 100%.
Of course, if the real part of the input Z is 0.02 Ohms, then it will be practically impossible to implement a matching network that will match this to 50 Ohms. Possibly with access to superconductors it might be!
Deborah