== Conventional Physical Optics (GO-PO) ==
The following analysis assumes a general impedance surface. The general impedance boundary condition relates the tangential components of the electric and magnetic fields on the surface: :<math> \mathbf{\hat{n} \times E(r)} = Z_s \mathbf{\hat{n} \times \mathbf{\hat{n} \times H(r)} </math> To treat an object with an arbitrary geometry using PO, the object is first decomposed into many small elementary patches or cells, which have a simple geometry such as a rectangle or triangle. Then, using the tangent plane approximation, the electric and magnetic surface currents, '''J(r)''' and '''M(r)''', on the lit region of the scatterer are approximated by:
:<math> \mathbf{J(r)} = (1+\alpha) \mathbf{\hat{n} \times H(r)} </math>