Abstract
In this letter, an antenna with a null-filled axisymmetric secant-square-shaped beam for the unmanned aerial vehicle (UAV) is proposed. The proposed antenna consists of four monopoles with sequentially rotated feed (SRF) and a coupling-fed grooved circular patch. The radiation power ratio of the monopoles and the patch is used to shape the axisymmetric beam. The effect of the ground is also investigated to operate positively on beam shaping. A prototype was fabricated to validate the method and the performance of the proposed antenna. The gain curves of the proposed antenna coincide well with the secant-squared (sec <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ) curve from θ = 0° to θ = 60° in all azimuthal angles with root mean square error (RMSE) below 1.35 dB in 5.5 GHz - 5.7 GHz.
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