Use of diffraction couplers in the analysis of the spatial structure of radiation

The example of a coarse grating made from cylindrical elements (wires) is used to analyze the diffracted fields in the near-field zone of a diffraction coupler, obtained for different angles of incidence and observation. The fundamental relationships are deduced and an analysis made of the conditions which must be satisfied to allow practical observation, in the near-field zone of the grating, of the diffracted field angular distributions similar to the far-field beam distribution. Experimental confirmation is reported of the validity of the results obtained and of the possibility of determining the angular distribution of radiation by making measurements in the near-field zone. The method is effective for an angular divergence of less than 10^–2.