Radio Electromagnetic Spectrum Frequency Bands

This chart shows the relative positions of the most common frequency bands, and is not to scale.

ELF = Extremely Low Frequency

VF = Voice Frequency

VLF = Very Low Frequency

LF = Low Frequency

MF = Medium Frequency

HF = High Frequency

VHF = Very High Frequency

UHF = Ultra High Frequency

SHF = Super High Frequency

EHF = Extremely High Frequency

January 2022 Update:

In response to my solicitation for information on the origin of band letter designations, a website visitor offered this:

I just looked at your web page that gives the names of the various RF bands, and, in one place asked for any information on origins of the names. I have some history on the band names that apply to UHF and above.

In the early days of radar (during WWII), the British and the U.S. researchers at MIT chose, arbitrarily I believe, letter designations for radar frequencies. The frequencies that were then possible to use for radio communication were just called by their "meter range" names: HF, VHF and UHF. The new frequencies that were then only used for deployable radar sets, and for new technology looking for even shorter wavelength radars, were given letter designations. So, in the 1940s and 1950s, radar sets were identified as being UHF, L-Band, S-Band, C-Band, X-Band and K-Band. Later they added Ku-Band - presumably for "K Upper," but I do not know. Later these became expanded with additional names for segments of spectrum, usually by the researchers or by their company marketing departments. I do not think the letters had any relational meaning - possibly this was a mild security measure. It seems unlikely that "Kurz" (German for "short") was any part of it since at the time the Germans were the enemy.

But there was an entirely separate community that also named segments of this same spectrum. This was the electronic warfare/electronic countermeasures researchers, companies and their military operators, and development and procurement agencies. They completely ignored "those radar guys" and invented their own spectrum segment designations. These segments were designated by letters in alphabetic order; starting with "A Band" at the low end and going upward with frequency. Some of the designators on your web pages are derived from this naming set. The band letter designators were physically implemented on the front panel band switches on ECM/ECCM sets. At least that was the case for USAF sets where the Air Force "EWO" (Electronic Warfare Officer) types used these letter designations exclusively and did not know what anyone meant if they used the "radar" band designations.

The "decade meter range" names were generally understood by everyone, but were treated as a broad generalization. The communications people were the custodians and protectors of these designations. (ULF, VLF, LF, MF, HF, VHF, UHF, etc.)

The "radar" bands are presently called "radar designations." The communications "decade/meter" names are called "the ITU designations," and the electronic warfare (EW) band names are called "the IEEE designations."

If you do a search on the origin of the designations for the various frequency bands, what you will find that nobody really knows. I have seen some pretty bogus explanations for how the band designation came to be, but I seriously doubt that the letters were assigned in order to confuse the enemy during WWII, or that "X" band was named for "cross," like in the cross hairs of precision targeting radars.

There is some logic in the upper and lower frequencies of the bands, however. The "3x10ⁿ" frequencies derive from wavelength in meters. Recalling that the speed of light in air is 300,000 km/s, that means a 1 meter wavelength translates to a frequency of 300 MHz, 10 meters is 30 MHz, 100 meters is 3 MHz, etc.

At some point, some wise soul decided that it was time to start over at a single digit for L-band at 1 GHz. The new regions are in octaves, except for 3 GHz, to 8 GHz. If anyone knows why 12.5, 18, and 26.5 GHz band edges were chosen, I would appreciate your letting me know.

Regarding the Ku, K, and Ka bands, supposedly K was named after the German word for "short," as in shortwave - Kurz. Ku is supposedly for K-under and Ka is supposedly K-above. That, of course, is inconsistent since since the K, if is derives from Kurz in wavelength, so K-under would be a lower (lesser) wavelength (hence higher frequency) and K-above would be a longer (greater) wavelength (hence lower frequency). Mostly likely, the certain origins are buried with their progenitors.

The ISM (Industrial, Scientific and Medical) frequency allocation is a crucial component of the radio frequency spectrum, which is the range of frequencies used for wireless communication and other purposes. This portion of the spectrum is set aside for unlicensed use, which means that any person or organization can use these frequencies without obtaining a license from the regulatory authorities. This allocation is designed to encourage innovation and the development of new wireless technologies.

In order to ensure the efficient use of the ISM frequency allocation and minimize the potential for interference with other wireless systems and services, each ISM frequency band has specific requirements and restrictions in terms of power output and other parameters. These requirements and restrictions vary depending on the specific frequency band and the country in which the device is being used.

The ISM frequency allocation is a valuable resource for unlicensed wireless communication and has enabled the development of a wide range of technologies and applications for industrial, scientific, medical, and consumer use. It has played a critical role in the growth of the Internet of Things (IoT) by providing a platform for low-power, short-range wireless communication between devices and has made it possible for consumers to enjoy the convenience of wireless communication and data transfer in their daily lives.