[pt] Este trabalho tem por objetivo um estudo da viabilidade de se fazer varreduras com uma antena gregoriana off-set com deslocamentos apenas do alimentador. São localizadas as regiões focais para a antena receptora de modo a posicionar o alimentador de uma maneira simples. Também são apresentados os diagramas de radiação correspondentes a estes deslocamentos calculados segundo a Teoria Escalar da Difração; e as limitações de varreduras para a antena particular que serviu para testar a eficiência do método. / [en] This work is related to the study of the pattern of Gregorian off-set antennas, by displacement of the feeder. The position of the feeder is obtained, in a simple way, by determining the focal regions of the antennas, working in reception. The radiation patterns corresponding to different position of the feeder are also presented. Such patterns are calculated according to the scalar theory of diffraction. The useful range of scanning, for a given antenna, used to check the efficiency of the method, is determined.

This discourse deals with a theoretical study of the radiation passage through a diffraction screen with non-zero size in the propagation direction of the radiation, i.e. the radiation passage through a three-dimensional object. Without any loss of generality, we solve the problem for cylindrical cavity in metal. The task exceeds evidently standard scalar theory of diffraction, thus we solve the problem using a waveguiding theory. Following the principles of the electromagnetic theory, we derive required formulae to determine mode distribution at the entry of the cavity. Further, we solve numerically the radiation propagation through the cavity, then we actually seek for radiation distribution at the very end of the cavity. This yields, with a help of the discrete Fourier transform, an intensity distribution of Fraunhofer diffraction pattern, consequently compared with an intesity distribution of the radiation pattern of Fraunhofer diffraction on infinitely thin circular opening having the radius of the cylinder cavity under study. A comparison of such patterns results to a conclusion, that the cavity length has a significatn influence on the diffraction pattern and more importantly, that the scalar diffraction theory appears incorrect for a coherent light passage through cavities longer than their radius squared. Similarly, the same conclusion is inversely proportional to a wavelength of the interacting radiation. Finally, we mention an existence of the so called "focal regime", when the radiation repeatedly exhibits roughly one order increased intensity on the symmetry axis of the cavity.

This diploma thesis deals with a design modification of detection part of the laboratory instrument for measuring the topography of rough surfaces – laser goniometric scatterometer (SM II). Design modification is based on replacement of so far used detector instead for the detector of higher quality with better measurement parameters. The first part of the diploma thesis contains theoretical basics, which are necessary to understand the relationship between scalar diffraction theory and scattering measurements of monochromatic light. The emphasis is on the importance of choosing appropriate detection coordinates, which are affecting the aberrations of detected diffracted light. The practical part is dedicated to improving the sensitivity of the detection part of the scatterometer SM II that is used in The laboratory of coherence optics at IFE FME BUT. This part justifies the choice of the detector which predetermines both the use of optical elements and the overall design of the detection part as the goniometer.