Abstract
A highly directive antenna of simple and lightweight structure is designed and tested experimentally. It consists of a dielectric rod with conical hole loading an open-ended circular waveguide. The test has shown that three different radiation patterns can be obtained depending on the depth of penetration of the rod inside the waveguide. Also an improvement on the axial gain can be obtained when the flare angles are smaller than <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">30\deg</tex> . The optimum design consists of a rod of conical flare angle of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7.5\deg</tex> which results in an improvement of 5 dB over the unloaded waveguide accompanied with a beamwidth which is half that of the unloaded structure. One practical application of the proposed design is its use as a feeder for parabolic reflectors, the advantage being the sharp nulls on both sides of the main lobe which will result in minimizing edge diffraction.
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