Theoretical analysis of a monopole antenna with conducting flat disk abovethe earth

The monopole antenna with a conductive ground above the earth is analyzed b y means of an equivalent circuit. The current distribution, input impedance , directivity, and antenna efficiency corrected for the effect of the elect rical 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 obtain ed by solving the circuit equation. From the numerical results by the metho d of moments, the input impedance and the antenna efficiency are found to d epend on the size of the radius of the grounding disk. In the absence of th e grounding disk, the antenna efficiency is higher for a larger antenna len gth. On the other hand, in the presence of the grounding disk, the antenna efficiency decreases as the antenna length is increased, and increases as t he antenna length is decreased. As regards the radiation pattern, the maxim um direction of radiation approaches the horizontal plane as the antenna le ngth is increased, and the beam width increases as the radius of the ground ing disk is increased. The effect of frequency is found to be small. (C) 20 01 Scripts Technica.