Investigations on ground compensation coils and their influence on the field distribution of electrically short loop antennas

Electrically small loop antennas are balanced devices by nature. Quite often such antennas are directly connected to a coaxial feed line e.g. the ISO/IEC 10373 test PCD antenna. The direct connection of such an antenna to the coaxial feed line leads to a mode conversion at the antenna terminals. In the present paper the influence of this mode conversion on the field distribution of an electrically short loop antenna is investigated in terms of finite element simulations applying an in-house software package. A method is introduced which allows the unbalanced mode excitation in the full wave simulation by prescribing appropriate boundary conditions.