**Physical Optics** (

PO) is a popular

Computational Electromagnetics technique used in

scattering analysis. It makes use of a simple

assumption to simplify the relationship between the

electric surface

currents on an object and the

incident EM wave that is causing the currents.

PO assumes that at any location on the scatterer, the surface curvature can be considered to be very small. It then extends that assumption to state that the local surface is to be considered flat and infinite in extent. Under these approximations, the electric surface current **J** can be written directly in terms of the incident magnetic field **H** as:

**J** = 2 **N** × **H**

where **N** is the local surface normal.
Using this relationship, the magnetic vector potential **A** can be
written as:

**A** = (μ / 4 π) ∫_{s} **J** (e
^{-jkR}/R) ds

where s is portion of the scatterer which is directly illuminated by the incident energy **H**.

The scattered electric field **E** is then simply:

**E** = -j ω **A**

in the far field.

The PO theory is very easy to implement, but has limitations which make it undesirable for use in the calculation of scattered fields from an object. It does not treat nonuniform currents which exist at joins and edges, which must be treated by seperate techniques such as the Physical Theory of Diffraction (PTD). It also does not take into account the issues of multiple bounce in a target which may have articulating parts, cavities, and the like. The method of Shooting and Bouncing Rays (SBR) must be used to handle this multibounce behavior. It also does not handle the scattering from cracks and gaps, or low-frequency effects such as creeping waves.