ENHANCED NEARFIELD RESOLUTION OF SMALL PHASE OBJECTS USING A PRIORI KNOWLEDGE

Amplitude and phase distributions in the nearfield behind small and weak double-bar phase objects (width and separation < wavelength lambda) measured with electro-magnetic 3 cm waves in TM-polarization (E-vector parallel to the bars) yield a rather poor agreement with the true phase object structure. However, for rectangular cross-sections of the phase object bars a simple expression of the angular spectrum of the diffraction field is available. The calculated amplitude of the angular spectrum is fitted to the angular spectrum of the measured nearfield distributions, with the dimensions (width, thickness, separation) of the phase bars as fitting parameters. The procedure yields an excellent reconstruction of the object sizes. It is not limited to the nearfield, but may be applied to the farfield, too.