Radiation pattern, impedance characteristics, and gain of a probe-excited rectangular ring antenna are investigated by the Method of Moments with the Rao-Wilton-Glisson (RWG-MoM) basis functions. The analysis is carried out for different lengths and positions of the probe as well as various lengths, widths and heights of the ring. In addition, the distribution of the surface current is also illustrated. Consequently, the suitable parameters are determined. It is obvious that the proposed antenna offers a bidirectional pattern with the impedance bandwith (|S11|< -10 dB) of 17%. Along the direction of the ring aperture, the gain is 5.28 dBi. Furthermore, the prototype antenna was fabricated and measured to verify the validity of the numerical calculation. It is found that the numerical and measured results are reasonably in good agreement.
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