Exact image method for impedance computation of antennas above the ground
Abstract
The principle of exact images recently developed by two of the present authors for the Sommerfeld problem is here applied for the classical impedance problem of antennas above the ground. In the present method, the effect of the ground is taken into account with an image source, which is located in complex space, leading to a modified Green function for the antenna current integral equation. The image of the antenna can be effectively determined through new expressions evaluated for the image current function. The stationary functional for the antenna impedance is extended to take into account the effect of the ground. As examples of the theory, impedance expressions for small dipoles and halfwave dipoles are formulated with numerical results calculated and compared with previous results. A simple method applicable for small microcomputers is suggested for calculating the impedance of wire antennas with finite thickness from that of infinitesimally thin antenna if the height of the antenna from the ground is not too small. Also, a practical method is suggested for the determination of ground parameters from horizontal lambda/2 dipole minimum resistance and height measurements.
 Publication:

IEEE Transactions on Antennas and Propagation
 Pub Date:
 September 1985
 DOI:
 10.1109/TAP.1985.1143712
 Bibcode:
 1985ITAP...33..937L
 Keywords:

 Antenna Design;
 Electrical Impedance;
 Dipole Antennas;
 Electrical Resistance;
 Functionals;
 Integral Equations;
 Sommerfeld Approximation;
 Communications and Radar