Abstract

The electromagnetic near field behind phase shifting half-planes (n = 1.02, thickness <2λ, distance 0.1λ-2λ) is investigated by using a modified Mach-Zehnder-interferometer for 3-cm microwaves and a small probe-antenna. Direct measurements of the diffraction fields are performed with high accuracy (amplitude 0.2%, phase 0.1°) and with high spatial resolution (<λ/30). The dielectric half-planes are approximated by parallel plates (width 36λ, height 17λ.) with wedge shaped edges, made of foamed polystyrene. They are fabricated inexpensively with high precision (thickness <λ/30, wedge angle <2°). The measured field distributions depend strongly on the wedge angle and the polarization of the incident radiation: For polarization with E-vector parallel to the edge the diffraction fringes are more pronounced than for perpendicular polarization. Behind rectangular edges the diffraction near field is symmetric, while it is strongly asymmetric behind wedge shaped edges. The measurements are confirmed by numerical calculations based on the first Born approximation for weak scattered taking into account the complex transmission of the incident wave inside the dielectric plate.

© 1992 Optical Society of America