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UBC Theses and Dissertations

Modifications to horn antennas which reduce beamwidth and back radiation Jazi, Ahmad Safaai


Modifications to horn antennas through choke flanges and parabolic cylinder reflectors are investigated. The latter are introduced to narrow the beamwidth, increase the gain and reduce the back radiation without increasing the horn length. The geometrical diffraction theory concepts and the Kirchhoff method are employed in the calculation of E-plane patterns of modified horns. The Kirchhoff method is applied to determine the fields reflected from the chokes and parabolic reflectors in the forward region where the geometrical diffraction theory fails. Very close agreement is obtained between the computed and measured patterns in the front region. In the rear directions the general level of back radiation for choked horns and the approximate lobe structure for horns with reflectors are predicted. Modification of horns by chokes results in a considerable reduction in the back radiation, but only a slight improvement in the beamwidth and the gain. Modification by parabolic reflectors, on the other hand, will result in a significant reduction in the beamwidth and substantial increase in the on-axis gain if the focal length of the reflectors is optimal. Considerably lower back radiation is also achieved.

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