The effect of flanges on the radiation patterns of small horns

This paper describes the results of experiments carried out on horns having rectangular apertures one dimension of which is of the order of a quarter of a wavelength, the other being of the order of one wavelength or more. The polarization is parallel to the smaller dimension. The paper considers the radiation pattern in a plane normal to the aperture of the horn and perpendicular to the longer sides of the aperture. The results are shown in a graphical scheme which demonstrates the types of radiation pattern resulting when various symmetrical systems of metal flanges are attached to the long sides of the aperture. The scheme shows the effect of variation of two parameters defining the flange system. These parameters are the length of the flanges and the angle contained between their planes. In particular it is shown within what limits the form of the radiation pattern can be regulated by this means, and to what extent it is possible to get patterns of a rectangular shape. It is also shown how various special types of pattern can be generated: e.g. patterns having a pronounced ¿dip¿ in the forward direction.