Extension of Babinet’s principle and the Andrews boundary diffraction wave to weak phase objects

Applying scalar diffraction theory in the near field of weak phase objects, we observed a simple relationship between the scattered field and the diffracted field behind an aperture of identical form in a black screen that permits a formulation of a modified scalar Babinet principle for complementary weak phase objects. Additionally, an empirical expression for the boundary diffraction wave of a perfectly conducting half-plane, derived by Andrews and Margolis [ C. L. Andrews D. P. Margolis , Am. J. Phys.43, 672– 676 ( 1975)], is adapted to phase-object near fields, which permits a simple numerical computation of the near fields of dielectric strips. The validity of both expressions is demonstrated with the use of a modified Mach-Zehnder interferometer for 3-cm microwaves.