Antenna design: The basic dipole
 
The simplest antenna or dipole, sometimes referred to as a Hertzian dipole, is sketched in figure 1. The length between the ends of the pair of conducting rods must be smaller than the wavelength of the radiation to be detected.
According to the radiation impinging on the system, the associated oscillating electric fields set up currents in the antenna which, in turn, produce fluctuating voltages across the resistor. The strengths of these are determined to provide measurements of the power received from the radio source. It may be noted that the primary currents in the rods are only generated by the electric fields in the radiation which are parallel to the lengths of the rods. The electric field disturbances within the radiation which are orthogonal to the rods’ axis have no effect in producing currents. Sensitivity only to electric field disturbances in the parallel direction to the rods means that the dipole is automatically sensitive to ‘one polarization’ associated with the received radiation.

Figure 1. A simple Hertzian dipole.