The antenna ground plane has to be of electrically conductive material like steel or aluminium (electrical isolators like fiberglass are therefore not suitable). It should be noted that the ground plane needs to be large enough compared to the size of the antenna for the antenna to perform properly. In addition, ground planes with a symmetrical shape are usually of advantage as an unsymmetrical ground plane may affect the radiation pattern of the antenna at certain frequencies – making the antenna radiate more to certain directions while decreasing its radiation performance in some other directions.
When using monopole antennas one should be aware that the exact installation location on the ground plane may have a very significant effect on how the antenna radiates in different directions. The best possible performance with a monopole antenna is typically achieved when having the antenna installed in the centre of the ground plane. Dipoles are less sensitive to a possible ground plane below them but may nevertheless be affected.