Definitions

Radio waves are electromagnetic waves occurring on the radio frequency portion of the electromagnetic spectrum. A common use is to transport information through the atmosphere or outer space without wires. Radio waves are distinguished from other kinds of electromagnetic waves by their wavelength, a relatively long wavelength in the electromagnetic spectrum.

## Propagation

Propagation is a term that describes the travel of electromagnetic waves, there being three main modes of propagation. The first is a straight line travel: the manner in which radio waves travel through deep space (ignoring the slight deviations caused by gravity under the theory of relativity). A second way is skip, which involves such waves bouncing between the surface of the earth and the ionosphere. Frequencies between 3 MHz and 30 MHz are most reliable for this kind of propagation, called High Frequency (see image at right). The third way is to hug the surface of the earth as it curves around. Radio waves of very low frequency most often travel this way.

Radio signals can also enter two ionospheric layers of differing electron densities and duct between them. The image at the right illustrates this. Two radio signals of differing elevation angles are broadcast into the ionosphere, where they split into ordinary (red) and extraordinary (green) components. In this example, the ordinary component began ducting between the E and F ionospheric regions.

Although this mode of radio wave propagation is less common than the skip mode, it is nonetheless an important mode because it permits radio signals to travel significant distances with little attenuation.

## Discovery and utilization

Radio waves were first predicted by mathematical work done in 1865 by James Clerk Maxwell. Maxwell noticed wave-like properties of light and similarities in electrical and magnetic observations and proposed equations that described light waves and radio waves as waves of electromagnetism that travel in space. In 1887 Heinrich Hertz demonstrated the reality of Maxwell's electromagnetic waves by experimentally generating radio waves in his laboratory. Many inventions followed, making practical use of radio waves to transfer information through space.

Nikola Tesla, Jagadish Chandra Bose and Guglielmo Marconi are credited with inventing systems to allow radio waves to be used for communication.

## Radio portion of the electromagnetic spectrum

Radio waves are divided up into bands by frequency (and corresponding wavelength) as shown in the radio frequency spectrum table below.

Band name Abbr ITU band Frequency
and
Wavelength in air
Example uses
< 3 Hz
> 100,000 km
Extremely low frequency ELF 1 3–30 Hz
100,000 km – 10,000 km
Communication with submarines
Super low frequency SLF 2 30–300 Hz
10,000 km – 1000 km
Communication with submarines
Ultra low frequency ULF 3 300–3000 Hz
1000 km – 100 km
Communication within mines
Very low frequency VLF 4 3–30 kHz
100 km – 10 km
Submarine communication, avalanche beacons, wireless heart rate monitors, geophysics
Low frequency LF 5 30–300 kHz
10 km – 1 km
Medium frequency MF 6 300–3000 kHz
1 km – 100 m
High frequency HF 7 3–30 MHz
100 m – 10 m
Very high frequency VHF 8 30–300 MHz
10 m – 1 m
FM, television broadcasts and line-of-sight ground-to-aircraft and aircraft-to-aircraft communications
Ultra high frequency UHF 9 300–3000 MHz
1 m – 100 mm
television broadcasts, microwave ovens, mobile phones, wireless LAN, Bluetooth, GPS and Two-Way Radios such as FRS and GMRS Radios
Super high frequency SHF 10 3–30 GHz
100 mm – 10 mm
microwave devices, wireless LAN, most modern Radars
Extremely high frequency EHF 11 30–300 GHz
10 mm – 1 mm
Above 300 GHz
< 1 mm

### Notes

• Above 300 GHz, the absorption of electromagnetic radiation by Earth's atmosphere is so great that the atmosphere is effectively opaque to higher frequencies of electromagnetic radiation, until the atmosphere becomes transparent again in the so-called infrared and optical window frequency ranges.
• The ELF, SLF, ULF, and VLF bands overlap the AF (audio frequency) spectrum, which is approximately 20–20,000 Hz. However, sounds are transmitted by atmospheric compression and expansion, and not by electromagnetic energy.
• The SHF and EHF bands are sometimes not considered to be a part of the radio spectrum, forming their own microwave spectrum.

## Named frequency bands

### General

• Longwave AM Radio = 148.5 - 283.5 kHz (LF)
• Mediumwave AM Radio = 530 kHz - 1710 kHz (MF)
• Shortwave AM Radio = 3 MHz - 30 MHz (HF)
• TV Band I (Channels 2 - 6) = 54 MHz - 88 MHz (VHF)
• FM Radio Band II = 88 MHz - 108 MHz (VHF)
• TV Band III (Channels 7 - 13) = 174 MHz - 216 MHz (VHF)
• TV Bands IV & V (Channels 14 - 69) = 470 MHz - 806 MHz (UHF)

The range of allowed amateur radio frequencies vary between countries. The article Amateur radio frequency allocations lists frequencies allocated for amateur radio use.

### IEEE US

Per IEEE Std 521-2002.
Band Frequency range Origin of name
HF band 3 to 30 MHz High Frequency
VHF band 30 to 300 MHz Very High Frequency
UHF band 300 to 1000 MHz Ultra High Frequency Frequencies from 216 to 450 MHz were sometimes called P-band: Previous, since early British radar used this band but later switched to higher frequencies.
L band 1 to 2 GHz Long wave
S band 2 to 4 GHz Short wave
C band 4 to 8 GHz Compromise between S and X
X band 8 to 12 GHz Used in WW II for fire control, X for cross (as in crosshair)
Ku band 12 to 18 GHz Kurz-under
K band 18 to 27 GHz German Kurz (short)
Ka band 27 to 40 GHz Kurz-above
V band 40 to 75 GHz
W band 75 to 110 GHz W follows V in the alphabet
mm band 110 to 300 GHz

### EU, NATO, US ECM frequency designations

Band Frequency range
A band 0 to 0.25 GHz
B band 0.25 to 0.5 GHz
C band 0.5 to 1.0 GHz
D band 1 to 2 GHz
E band 2 to 3 GHz
F band 3 to 4 GHz
G band 4 to 6 GHz
H band 6 to 8 GHz
I band 8 to 10 GHz
J band 10 to 20 GHz
K band 20 to 40 GHz
L band 40 to 60 GHz
M band 60 to 100 GHz

### Waveguide frequency bands

Band Frequency range
R band 1.70 to 2.60 GHz
D band 2.20 to 3.30 GHz
S band 2.60 to 3.95 GHz
E band 3.30 to 4.90 GHz
G band 3.95 to 5.85 GHz
F band 4.90 to 7.05 GHz
C band 5.85 to 8.20 GHz
H band 7.05 to 10.10 GHz
X band 8.2 to 12.4 GHz
Ku band 12.4 to 18.0 GHz
K band 15.0 to 26.5 GHz
Ka band 26.5 to 40.0 GHz
Q band 33 to 50 GHz
U band 40 to 60 GHz
V band 50 to 75 GHz
W band 75 to 110 GHz
Y band 325 to 500 GHz