Centimeter waves (microwave radio waves) are a frequency range of radio waves with wavelengths from 1 to 10 cm, or frequencies from 3 to 30 GHz (super high frequencies, SHF).
Propagation of Centimeter-Range Radio Waves
Centimeter-range SHF waves are primarily used for radar and radio relay communications. The propagation characteristics of radio waves in this range differ significantly from those of longer-wavelength ranges.
The first distinctive feature of centimeter-wave propagation is the almost complete absence of diffraction and the straight-line nature of propagation. The Earth's surface has virtually no noticeable effect on the propagation of these radio waves, which is due to the use in this range of narrow-beam antennas with a radiation pattern width from a few degrees to fractions of a degree (mostly aperture antennas). The second distinctive feature of microwave propagation is the high atmospheric absorption of energy, especially during rain, snow, frost, dust, fog, hail, as well as during sharp movements of warm and cold air layers.
Meteorological conditions typical for the lower layers of the atmosphere — the troposphere — significantly affect the propagation of microwaves. The state of the troposphere changes almost continuously, and so does the field strength of microwaves. Signal fading can be both short-term and long-lasting.
The field strength of microwaves can be calculated using formulas applied to the very high frequency range, but with additional allowances for losses due to absorption and scattering of electromagnetic energy by atmospheric particles.
Increased scattering and absorption of microwaves during various atmospheric phenomena make it possible to use radio waves to monitor weather conditions (for detecting approaching rain, storms, snowfall, etc.). The absorption of microwaves by raindrops increases as the wavelength shortens and as rainfall intensity grows. Thus, centimeter-range radio waves can be effectively used for cloud observation. Longer waves are unaffected by clouds and rain, and radars operating on such waves are suitable for any weather unless cloud monitoring is the specific task.
Radiation in this range has diverse applications in modern technology. For example, the standard frequency for microwave ovens and industrial plasma SHF installations is 2.45 GHz. This is the resonance absorption frequency for water molecules, and since all food products contain water, an SHF oven at this frequency can efficiently heat any product. Furthermore, at this frequency, the atmosphere is opaque due to absorption by water vapor.
Related articles: HF, Frequency range, Short radio waves, Ultra short waves (VHF, Very High Frequency), Satellite frequency table