Geometrical Optics (GO) Based on Ray Launching
- Geometrical Optics (GO) based on Ray Launching
RCS of an aircraft at 1 GHz in the elevation plane: Comparison between
MLFMM and GO (ray launching). GO (ray launching) required 33 times
Ray launching through a lens. Dielectric lens modelling with GO
General Applicability of the Technique
GO (ray launching) is formulated for use in instances where electrically very large (> 20 λ) metallic or dielectric structures are modelled. GO is a ray-based technique that models objects based on optical propagation, reflection and refraction theory. This is also known as the shooting and bouncing rays (SBR) approach.
Users will typically attempt a MoM solution for structures involving such objects at first and should they find that the structure is electrically too large to solve using available resources (platform memory, time) they will turn to MLFMM and then GO.
FEKO integrates the GO method with the current-based MoM, by launching rays from each radiating MoM element. The ray-interactions with metallic and dielectric structures are then modelled using Huygens sources placed on each ray-contact point (reflected, refracted and transmitted rays) on the material boundaries. The ray-launching process is easily controlled based on the angular spacing (for localised sources) or transverse spacing (for plane wave sources) of the rays and the number of interactions to be taken into account.
FEKO segments a GO region triangularly, in exactly the same manner used for MoM and PO solutions, making it a simple task to switch between solution options. GO triangles may, however, be electrically much larger than for MoM modelling as the mesh only needs to resolve the surface geometry, potentially resulting in a large reduction in mesh storage requirements. Smooth surfaces can be meshed into very few triangles, independent of the wavelength.
Run-time and memory requirements scale almost perfectly for parallel processing. Multi-core CPUs or cluster computers thus operate very efficiently while solving GO (ray launching) problems.
GO (ray launching) models may include various complex dielectric materials:
- dielectric coatings of metallic surfaces
- thin dielectric sheets with multiple dielectric layers
- anisotropic materials
Traditional GO FEKO extended GO GO (ray launching) complex material modelling
Radiation Analysis with GO (Ray Launching)
For dielectrics, a typical application of the MoM/GO hybrid method is the analysis of lenses. The source structure, e.g. a metallic antenna under a lens, may be modelled with the MoM and the large dielectric lens may be modelled with the GO.
For metallic structures, an ideal application is the analysis of reflector antennas. The feed source can often be modelled in isolation to establish its radiation pattern. The pattern can then be imported into the GO-based analysis of the reflector, as its excitation.
Reflector near field calculated with GO Comparison between GO and MLFMM
Scattering Analysis with Ray Launching GO
For highly accurate solutions to scattering problems the premier method is full wave analysis with the MoM (or MLFMM). For electrically very large structures, an asymptotic method is required as any full wave method results in prohibitive resource requirements. PO may require a prohibitively large mesh for extremely large problems, while run-time grows exponentially with multiple reflections. GO (ray launching) is inherently well suited to the solution of large structure scattering problems, since the “shooting and bouncing rays” approach is very efficient for an arbitrary number of multiple reflections. RCS can be computed with RL-GO, which is not possible with UTD due to caustics.