Spurious solutions on Dispersion Diagram

[kalo]

Hi all,

I'm trying to obtain the dispersion relation of EBG structures,
I' m using a software based on MoM,
but some spurious solutions appear, these spurious lie in the linear relation (in (straight) line).

Why do these spurious solution appear?
Is there a theoretical reason to neglect them?
Does someone help me?

Thanks in advance.

Regards.

 

[savedadogs]

Can you please post a picture of your structure and the dispersion diagram that you obtained. Most likely it is a numerical error. Dispersion diagrams are tricky especially in the fast wave region.

 

[kalo]

More details:
The MoM analisys is based on Electric Field Integral Equation (EFIE) and leads to the formulation of a homogeneous matrix problem.
The solution of this problem is performed by an iterative procedure:
for a given value of the propagation phase constant beta,
the frequency range is scanned to find the frequencies where the field equation has a non trivial solution.
The search of these frequency is based on the detection of the determinant zero crossing.
In this context I'm obtaining spurious solution, which lie in line,
as if the FSS structure was a non dispersive structure for these spurious solution.
The unit cell is a square patch (lenght=0.6 cm, periodicity=0.8 cm, substrate thickness=0.254 cm, permettivity=10.2)
An example is on the attached file.