HFSS: question about radiation pattern

[tkk_hut]

Hi, I hope this is the correct forum. I was wondering if anyone has used Ansoft HFSS and could help me with a simple problem.

My goal is to see what kind of radiation pattern an antenna or waveguide has if we substitute air with teflon. So basically when normally an antenna radiates into air, now the open space would be filled with teflon. I hope I'm making sense. Anyway, this sounds like a simple problem but since I'm pretty much a complete newbie with hfss, i'd just like to make sure i understand what I'm doing. So, normally when you want to explore the radiation pattern of a waveguide for example, you create the waveguide which is surrounded by an airbox with radiation boundary. Analyse, create farfield setup and plot the radiation pattern. So in my case i should just fill the airbox with teflon instead air, am I right?

Thank you in advance

 

[vk6kro]

The teflon would reduce the resonant frequency of the antenna slightly, but it would still radiate very effectively at the new frequency because teflon has very low loss.

There is a wonderful free program called EZNEC DEMO which is available from the author's website. This has a data entry system where all conductors in an antenna are called "wires". There is an option there to add a dielectric of any thickness to any of the wires.

I added a dielectric of dielectric constant of 10, and 5 inches thick, to an existing loop antenna for 75 MHz. This dropped the resonant frequency of the loop from 75.2 MHz to 73.0 MHz.
Not much change.

This is understandable as the new material is having only a small effect on the capacitance of the antenna to ground, because there is a very large thickness of air between the antenna and grond.