hfss resonance dip

I recently used IE3D 11.15 to compute the back scattering RCS for a square conductor sitting on top of an infinite dielectric slab with a finite ground conductor (also a square). The excitation was an normally incident plane wave. The code reports a peak (highest) value RCS for (theta0,phi=0) at a frequency of resonance.

I had also used HFSS to compute the back RCS for the same pa-tch on top of a finite dielectric slab with finite ground. The HFSS results show a dip at roughly the same frequency (of resonance). Thus the two codes "seem" to give contradicting answers.

I look forward to your opinions on
1) definition of RCS in IE3D.
2) should there be a peak or a dip for the back scattering RCS when a plane wave is incident upon a square conductor sitting on top of a finite dielectric slab with finite ground.
3) is there any difference in the definition of RCS for planar geometry with infinite or finite ground inside IE3D. (Altough I used infinite dielectric in IE3D, the intension was to model a finite dielectric with finite ground. )

Hi, poyinting:

On IE3D, the scattering field is defined as the field scattered instead of reflected. When you define infinite substrate, there is scattered field and reflected field. Reflected field is a plane wave when the incident wave is planewave. Scattered field is a spherical wave.

In some sense, if you model a patch on infinite substrate and a patch on finite substrate, you may not get the same scattered field because the scattered field from the finite substrate is included in the finite case while the reflected wave from the infinite substrate is not included in the infinite case.

On IE3D 11.5, I don't think we support RCS with finite substrate. Planewave excitation and RCS calcualtion for finite substrate are supported in IE3D 12.

Best regards,