Theoretical analysis of a monopole antenna with conducting flat disk above the earth

The monopole antenna with a conductive ground above the earth is analyzed by means of an equivalent circuit. The current distribution, input impedance, directivity, and antenna efficiency corrected for the effect of the electrical characteristics of the earth are derived in terms of parameters such as the antenna length, the radius of the grounding disk, and the frequency. First, by means of the plane wave expansion, the system is represented by an equivalent circuit in the spectral domain and Green's function is obtained by solving the circuit equation. From the numerical results by the method of moments, the input impedance and the antenna efficiency are found to depend on the size of the radius of the grounding disk. In the absence of the grounding disk, the antenna efficiency is higher for a larger antenna length. On the other hand, in the presence of the grounding disk, the antenna efficiency decreases as the antenna length is increased, and increases as the antenna length is decreased. As regards the radiation pattern, the maximum direction of radiation approaches the horizontal plane as the antenna length is increased, and the beam width increases as the radius of the grounding disk is increased. The effect of frequency is found to be small. (C) 2001 Scripts Technica.