title: Aperture-to-medium coupling loss
text: # Aperture-to-medium coupling loss
  
  In telecommunication, aperture-to-medium coupling loss is the difference between the theoretical antenna gain of a very large antenna, such as the antennas in beyond-the-horizon microwave links, and the gain that can be realized in practice.
  
  Note 1: Aperture-to-medium coupling loss is related to the ratio of the scatter angle to the antenna beamwidth.
  
  Note 2: The "very large antennas" are referred to in wavelengths; thus, this loss can apply to line-of-sight systems also.
  
  