This paper concerns an experimental and theoretical study of the amplitude and phase structure of the image of a point source, formed by an ideal microwave-lens focusing system having its circular aperture partially obscured by disks or sectors of various sizes located in the aperture plane. The f/D ratio, the wavelength and the aperture diameter are respectively 2.7, 3.2 cm and 19.5 wavelengths. The exact Helmholtz-Kirchhoff formula is used in the numerical computations and is compared with the Rayleigh formulas.
Diagrams are presented, showing measured and calculated fields and their characteristics are discussed. In the case of asymmetrical apertures, only the amplitude distribution is symmetrical in the focal plane, whereas the phase is not and both the amplitude and phase are unsymmetrical in all other regions.
B. G. WHITFORD and T. J. F. PAVLASEK, "Focal-Region Fields of Annular and Sectoral Microwave Apertures," J. Opt. Soc. Am. 58, 1591-1595 (1968)