I would like to know how to model an antenna above an underground metal plate in NEC4.2 or CST?
I need such a model to find out what is the influence of a metal plate of 21 x 21 meters that is buried 5 centimeters under lossy ground on a turnstile antenna of two inverted vee (thin) dipoles on the polarization, and the influence of position errors on the diagram and the polarization.
I have extensive experience with NEC4.2, but so far my experience is limited to wire antennas above ground. I have only modeled ground screens above ground, not just below it.
Hoi Ben,
First question is: what will be the wavelength of the EM wave? Is it much smaller than 21m? I would 1/10 of 21 m = 2.1 meter or smaller as small. Then I would just use an infinite conductive groundplane which should be available in NEC4.2. (I've got experience with 4NEC2 and modelling of marine type antennas above the metal and/or sea.)
Otherwise, if your wavelength cannot be considered to be small, I'd try with a GP from 21 m long metal rods which are spaced at 1/10 or 1/20th of a wavelength.
To simulate the influence of the soil you'll have to use CST, since this is not a simple dielectric or metallic piece of wire.
Sorry, I should have specified that: 5.3 MHz. And no, a radial network won't properly represent the metal plate, although a mesh network could. NEC4.2 also has dielectric (Sommerfeld) ground, but I just don't know how to create a correct underground plate or mesh. Neither in NEC nor in CST. Any example files?
Hello Ben,
Since you are asking the question, then I suppose that your computational capabilities are not enough to run the simulation.
In this case, I would suggest to scale your problem in frequency:
1- Calculate the electrical lengths of both your antenna and ground plane
2- Choose the smallest frequency that will allow you to run your simulation on your computer
3- Get the new physical dimensions of your antenna and ground plane by using the new wavelength
4- Make sure to keep a good impedance matching at the new operating frequency
5- Run your simulation and pray that the results would be close to those at 5.3 MHz :o)
Hi Farid, thanks for your advice! I have enough computation power to run the simulation, but need advice on the correct way to model the underground metal plate or underground metal mesh. Preferably without as little necessity for prayer to make the results realistic, although it may always help ;-)
Hi Ben,
If you have enough computation power, then I am not sure to understand the problem.
If you have the necessary computation power, is there any problem to draw in CST a square metallic layer that would be the metallic ground plane and then add another dielectric layer that would represent the lossy ground and then draw the antenna on the top?
Select ground plate & put metal plate on that ground plane then add substrate & patch.
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