RF designers frequently need to know the true power density or field intensity at a particular distance from a transmitter. Calculations for them are important when attempting to estimate electromagnetic-interference (EMI) effects, determining potential radiation hazards (for personnel safety) as well as verifying or establishing specifications.
Field intensity, or field strength, is defined as the magnitude of the electric field vector, typically expressed in volts/meter (V/m). With frequencies higher than 100 MHz, and more importantly above 1 GHz, power density (PD) is quite frequently used more than field strength.