In a normally-operating antenna, positive and negative charges have no way of leaving and are separated from each other by the excitation "signal" (a transmitter or other EM exciting potential). This generates an oscillating (or reversing) electrical dipole, which affects both the near field and the far field. In general, the purpose of antennas is to communicate wirelessly for long distances using far fields, and this is their main region of operation (however, certain antennas specialized for near-field communication do exist).