free space propagation model

Free Space propagation model

The Free Space model of path loss (FSPL) is the simplest one of radio propagation model. It is the loss of the signal power of an electromagnetic wave in a direct sight transmission line (line-of-sight). This empirical model does not include some factors such as the gain of the antenna used for the emission and the reception and the losses related to the material imperfections.

Free-space is proportional to the square of the distance between the transmitter and the receiver, also to the square of the radio signal frequency.

The equation for the FSPL is:

Free Space propagation equation


  • λ: Signal’s wavelength (in Meters)
  • f: signal frequency (in Hertz)
  • d: Transmitter Distance (in Kilometers)
  • c: light speed (3 x 108 Meters per second)

This equation is exact only in a remote field; it is not valid near the transmitter. This model belongs to the family of Free space loss.