Abstract
We present an analytical formula for the radiation resistance of planar short monopole antennas. The linear element of the antenna is placed parallel to a ground plane, extending beyond its edge. The approach, based on the solution for scattering of a plane wave impinging on a perfectly conducting half-plane, uses a combination of the reciprocity theorem, Fresnel integral approximation, and Poynting theorem to derive an analytical expression for the radiation resistance of such monopoles shorter than about lambda/10. The analytical results are in very good agreement with measurements and numerical simulation results carried out for a large and finite-size ground plane. It is found that the short planar monopole shows a radiation resistance that has a dominant term depending linearly-instead of quadratically-on the monopole height, thus providing relatively high values for quite short lengths. The same methodology is also applied to the case of a planar short dipole parallel to the half-plane's edge. However, a much lower radiation resistance is obtained in that case. The impact of these results on bent planar monopole designs is briefly discussed.
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