Suppose a structure was 1/2 wavelength long. If time is not taken into account,
coupling might be in phase. If time is taken into account, coupling might
be 180 degrees out of phase. Big difference! My good friends at IBM, Al
Ruehli and Barry Rubin, call this the retardation effect. I'm sure they could
comment further on this.
I think that MoM can be used on structures as large as a wavelength, only if
coupling at large fractions of a wavelength are insignificantly small.
> I agree with you that your friend is wrong in stating the entire structure
> has to
> be less 1/10 wavelength to use MoM. Instead, the structure has to be
> in such a way that each element is very small compared to wavelength.
> 1/10 wavelength is a good rule of thumb. One may go as high as 1/20
> to achieve higher accuracy. This is because many MoM formulation uses so
> locally supported basis function to represent electric currents. Those
> are typically low order polynomials. Hence, it only can represent small
> in currents on a local area such as a triangle or rectangle.
> -Xingchao Yuan
> Cadence Design Systems