Modelling antenna-ground interactions

The properties of antennae change significantly when they are brought close to the ground surface. Consequently the optimum design of ground penetrating radar (GPR) systems is strongly dependent on a detailed understanding of the interaction of the antenna and the neighbouring ground surface. The Numerical Electromagnetics Code (NEC) is a computer program for antenna modelling which uses integral equations to model wire-like objects and closed surfaces and can model loading and ground effects. NEC provides an attractive alternative to laboratory or field testing of antennas close to the ground surface as antenna configurations and ground conditions can be changed easily. It has the capability to detennine the electromagnetic field strength above and below the ground surface and in close proximity to the antennas where GPR measurements are made. The input impedance of the antenna can also be calculated.