Radio propagation

Radio propagation is the transmission of radio waves through space and materials. Their paths and strengths change through reflection, diffraction, scattering, absorption, and interaction with the atmosphere.

Electromagnetic wave: A traveling disturbance of electric and magnetic fields that carries energy through space or matter. Radio waves are electromagnetic waves, governed by the same basic propagation principles.
Free-space path loss: The reduction in received power as a radio wave spreads through unobstructed space. It provides a baseline for estimating signal strength before atmospheric or obstacle effects.
Radio wave: An electromagnetic wave with a frequency in the radio portion of the spectrum. Propagation describes how these waves move and change between transmitter and receiver.
Ground wave: A radio wave that follows Earth’s surface through diffraction and electromagnetic interaction with the ground. It contrasts with skywave propagation, which returns signals from the upper atmosphere.
Radio channel: The physical medium and propagation conditions through which a radio signal travels between transmitter and receiver. Propagation effects collectively shape the channel’s delay, fading, and frequency response.
Reflection (physics): The return of a wave from a boundary between materials or from a surface. Reflected radio waves create multipath signals and can extend coverage beyond direct paths.
Link budget: An accounting of transmitted power and gains and losses along a communication link. Propagation losses and fading determine whether a radio link has enough power margin.
Wavelength: The distance between successive corresponding points in a wave, such as adjacent crests. Wavelength influences diffraction, penetration, antenna behavior, and sensitivity to obstacles.
Skywave propagation: Radio transmission over long distances through refraction in the ionosphere back toward Earth. It reaches beyond the horizon, unlike ordinary ground-wave and line-of-sight paths.
Fading: Variation in received signal amplitude or phase caused by changing propagation paths and conditions. Fading captures rapid and slow fluctuations that a single path-loss estimate cannot describe.

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