The Kobayashi potential in electromagnetic theory is reviewed. As an illustration we consider two problems, diffraction of plane wave by disk and rectangular plate of perfect conductor. Some numerical results are compared with approximated and experimental results when they are available to verify the validity of the present method. We think the present method can be used as reference solutions of the related problems.

Electromagnetic scattering of an electromagnetic plane wave from a rectangular hole in a thick conducting screen is solved using the Kirchhoff approximation (KA). The scattering fields can be derived as field radiations from equivalent magnetic current sources on the aperture of the hole. Some numerical results are compared with those by the Kobayashi potential (KP) method. The proposed method can be found to be efficient to solve the diffraction problem for high frequency regime.