Formation of an Axially Symmetric Field Distribution Using Rectangular Aperture Radiators

Abstract

Using the aperture method, radiation from the open end of a rectangular waveguide was studied. Expressions were derived to describe the radiation pattern of such an aperture in the far-field region in two mutually perpendicular planes. Numerical studies of the radiation pattern cross-sections in the image plane were performed for two rectangular apertures, 40×33 mm and 30×21.6 mm, with varying aperture widths and heights. A comparison of the obtained radiation pattern cross-sections with a Gaussian field distribution showed that up to the –11 dB level, the radiation pattern cross-sections in both image planes practically coincide with the Gaussian field distribution. This result is particularly important when a wave beam is incident on the flat face of an axicon. It was also shown that varying the smaller dimension of the rectangular aperture can yield an axially symmetric radiation pattern. Experimental studies of these apertures in the K_a band were conducted. Good agreement between the experimental results and theoretical calculations was demonstrated. It was found that when the geometric dimensions of the rectangular aperture exceed two wavelengths, a traveling-wave regime is established in the waveguide section. Experimentally, it was found that the amplitude distribution of the field for both apertures in the far-field region coincides with the Gaussian distribution down to –8.7 dB. It was shown that the use of rectangular apertures to illuminate the flat face of an axicon with a wave beam is impractical.