Altair Feko: Radome Modelling with MoM Characterised Surfaces: Workflow & Limitations
Altair EmployeeWorkflow
1) Calculate Transmission & Reflection (TR) coefficients of a planar layered structure and export to *.tr file.
Use the Planar Multilayer Substrate solution for isotropic layered structures or Periodic Boundary Condition solution for FSS type structures.
- Use normal plane wave incidence vs frequency: {theta, phi} = {0,0} with orthogonal polarisations.
- Phase reference position at the top of the layered structure.
- Export to *.tr file.
Can re-use a *.tr file that was previously used with the RL-GO asymptotic solution assuming that the phase reference position was at the top of the layered structure.
2) Define a characterised surface on air (εr=1) dielectric region solved with the SEP MoM / MLFMM solution.
Example 1: Modelling a single layer radome with a characterised surface.
Figure 1: Single dielectric layer radome (some faces are hidden) excited with a Hertzian dipole array
The characterised surfaces must be applied to an air dielectric region solved with SEP MoM/MLFMM. Can use the inner surface of the radome layer together with the metallic backplate to form an air dielectric region.
- Apply characterised surface on the inner surface of actual layered structure.
- Face normal of the characterised surface must point towards the source.
- Specify total layer thickness.
- Reference vector not used (yet).
Figure 2: Single layer radome modelled via characterised surfaces on a closed air dielectric region
Example 2: Modelling a FSS radome with a characterised surface
Figure 3: Cylindrical radome with single εr=2.2 dielectric layer with hexagonal slot FSS surface in the middle.
Again, the characterised surfaces must be applied to an air dielectric region solved with SEP MoM/MLFMM. In this case an option is to remove the FSS surface and change the properties of the dielectric layer to air. Note the air dielectric layer thickness can be chosen to some convenient value related to the mesh size. The characterised surface is applied on the surface closest to the source.
Figure 4: Cylindrical FSS radome modelled via characterised surfaces
Limitations of the characterised surface approximation
- The TR coefficients are calculated for a planar structure with plane-wave incidence. When used as a characterised surface the incident field on the characterised surface should be locally plane. This imply that the source can’t be too close to the characterised surface and that the radius of curvature of the characterised surface should be small. Ideally the surface radius of curvature should be >> λ .
- Presently normal incidence is assumed when enforcing the boundary conditions and the source should illuminate the characterised surface close to normal incidence. Preferable not more than 30° off normal.