THICK GRIDS WITH CIRCULAR APERTURES - A COMPARISON OF THEORETICAL ANDEXPERIMENTAL PERFORMANCE

In this paper a comparison between a rigorous electromagnetic model fo r transmission through a hexagonal array of circular waveguides in a s eries of thick, metallic screens and experimental measurements in the far infrared is made. It is found that there is excellent agreement be tween theory and experiment when the frequency is below that where any diffracted orders propagate. The agreement is still very good above t his frequency. Below a frequency approximately equal to the cut-off fr equency of the circular waveguides little power is transmitted. As the thickness of the screen is increased, this decrease in transmission b ecomes more abrupt. Also, for thick screens, resonances appear in the transmission spectrum which are analogous to those which appear in the spectra of two grids separated by a distance comparable to the wavele ngth of the radiation being used.