Ray-Tracing With Physical Optics And MEC
Physical Optics (PO) is a ray-based physics technique that is very effective for radar scattering and other applications that require calculation of backscatter from detailed faceted objects.
Unlike methods based on the GO/UTD approach, PO involves a full surface integration over faceted structures. This requires denser ray tracing and is more computationally intensive than geometric optics and UTD; however, the additional computation can provide much more accuracy for calculations that require analysis of scattering from faceted structures that are highly detailed, such as the calculation of radar backscatter from a finely-faceted model of a vehicle, aircraft, or naval vessel, or reflections from other high-resolution surfaces. Traditional approaches often make far-field assumptions and are applied to problems such as the calculation of far-field RCS. In Remcom’s WaveFarer® radar analysis software, however, the technique has been specifically enhanced to account for near-field effects, allowing the method to be applied to closer-range applications such as automotive radar or indoor sensing.
In PO, a scattering object is composed of a set of facets that define a closed surface. Ray-tracing is used to find paths to every facet on this closed surface, potentially incurring multipath interactions with other surfaces along the way. It can be combined with GO/UTD methods to incorporate the effects of multipath interactions with other structures in the environment into its calculation of the electromagnetic fields incident on each facet of the surface. The surface integration requires very dense paths, which Remcom’s solutions achieve by targeting facets and incorporating extensions to multipath rays that intersect a target’s geometry. Figure 1 shows an example of the top 50,000 paths for an automotive radar scenario. Once paths are found, the received voltages for each path to each facet are calculated using a generalized Green’s function. The total received voltage at an antenna is then calculated from the sum of the contributions from all combinations of paths and the facets with which they interact.
Method of Equivalent Currents (MEC)
While physical optics does include the effects of edges in its scattering calculations, these effects can be further improved through corrections based on techniques such as the Method of Equivalent Currents (MEC). Remcom’s solutions have applied MEC to find equivalent electric and magnetic currents associated with each edge, which are then included in line integrals to supplement the PO surface integral. The result produces a better numerical approximation for near-zone or far-zone scattered fields than surface PO alone.