sci.physics.electromag

On Wed, 13 Feb 2008 11:45:58 +0100, Joerg Felder
wrote:

>Hi everybody,
>
>I have been toying around with some matlab code for FDTD simulations.
>Running a simulation for a patch antenna, I get S parameters just slightly
>larger than 0dB below a few hundred MHz. My assumption is that I have
>either a DC offset in the simulation or the excitation pulse does not
>sufficiently cover DC frequencies. However, the behavior is similar for
>both, a gauss pulse as well as a derived gauss excitation...
>
>Does anybody have an idea and could give me hints where to look at.

You could try using an excitation pulse which has no DC component,
such as a sinusoid modulated by a raised cosine. If you still get the
problem then it isn't DC offset.

Another, more likely, reason is that your absorbing boundaries are not
perfect and some reflections are perturbing your S parameter
calculations. Are you using PML or just something like Mur?

Good luck

--

Fergus