What is BAND ?

 A specific range of frequencies (for example those between 1850 MHz and 1995 MHz) are called a band.

A radio band is a small contiguous section of the radio spectrum frequencies, in which channels are usually used or set aside for the same purpose. To prevent interference and allow for efficient use of the radio spectrum, similar services are allocated in bands. For example, broadcasting, mobile radio, or navigation devices, will be allocated in non-overlapping ranges of frequencies.For each of these bands the ITU has a bandplan which dictates how it is to be used and shared, to avoid interference and to set protocol for the compatibility of transmitters and receivers.

•  ITU

As a matter of convention, the ITU divides the radio spectrum into 12 bands, each beginning at a wavelength which is a power of ten (10ⁿ) metres, with corresponding frequency of 3×10⁸⁻ⁿ hertz, and each covering a decade of frequency or wavelength. Each of these bands has a traditional name. For example, the term high frequency (HF) designates the wavelength range from 100 to 10 metres, corresponding to a frequency range of 3 MHz to 30 MHz. This is just a naming convention and is not related to allocation; the ITU further divides each band into subbands allocated to different uses. Above 300 GHz, the absorption of electromagnetic radiation by Earth's atmosphere is so great that the atmosphere is effectively opaque, until it becomes transparent again in the near-infrared and optical window frequency ranges.

These ITU radio bands are defined in the ITU Radio Regulations. Article 2, provision No. 2.1 states that "the radio spectrum shall be subdivided into nine frequency bands, which shall be designated by progressive whole numbers in accordance with the following table.

The table originated with a recommendation of the IVth CCIR meeting, held in Bucharest in 1937, and was approved by the International Radio Conference held at Atlantic City, NJ in 1947. The idea to give each band a number, in which the number is the logarithm of the approximate geometric mean of the upper and lower band limits in Hz, originated with B.C. Fleming-Williams, who suggested it in a letter to the editor of Wireless Engineer in 1942. 

• EU, NATO, US ECM frequency designations

NATO LETTER BAND DESIGNATION						BROADCASTING BAND DESIGNATION
NEW NOMENCLATURE			OLD NOMENCLATURE
BAND	FREQUENCY (MHz)		BAND	FREQUENCY (MHz)
A	0 – 250		I	100 – 150		Band I 47 – 68 MHz (TV)
						Band II 87.5 – 108 MHz (FM)
			G	150 – 225		Band III 174 – 230 MHz (TV)
B	250 – 500		P	225 – 390
C	500 – 1 000		L	390 – 1 550		Band IV 470 – 582 MHz (TV)
						Band V 582 – 862 MHz (TV)
D	1 000 – 2 000		S	1 550 – 3 900
E	2 000 – 3 000
F	3 000 – 4 000
G	4 000 – 6 000		C	3 900 – 6 200
H	6 000 – 8 000		X	6 200 – 10 900
I	8 000 – 10 000
J	10 000 – 20 000		Ku	10 900 – 20 000
K	20 000 – 40 000		Ka	20 000 – 36 000
L	40 000 – 60 000		Q	36 000 – 46 000
			V	46 000 – 56 000
M	60 000 – 100 000		W	56 000 – 100 000
US- MILITARY / SACLANT
N	100 000 – 200 000
O	100 000 – 200 000

• IEEE radar bands

Frequency bands in the microwave range are designated by letters. This convention began around World War II with military designations for frequencies used in radar, which was the first application of microwaves. Unfortunately, there are several incompatible naming systems for microwave bands, and even within a given system the exact frequency range designated by a letter may vary somewhat between different application areas. One widely used standard is the IEEE radar bands established by the US Institute of Electrical and Electronics Engineers.

Radar-frequency bands according to IEEE standard

Band designation	Frequency range	Explanation of meaning of letters
HF	0.003 to 0.03 GHz	High Frequency
VHF	0.03 to 0.3 GHz	Very High Frequency
UHF	0.3 to 1 GHz	Ultra High Frequency
L	1 to 2 GHz	Long wave
S	2 to 4 GHz	Short wave
C	4 to 8 GHz	Compromise between  S and X
X	8 to 12 GHz	Used in World War II for  fire control, X for cross  (as in crosshair). Exotic.
Ku	12 to 18 GHz	Kurz-under
K	18 to 27 GHz	Kurz (German for 'short')
Ka	27 to 40 GHz	Kurz-above
V	40 to 75 GHz
W	75 to 110 GHz	W follows V in the alphabet
mm or G	110 to 300 GHz​	Millimeter

1. ^ The designation mm is also used to refer to the range from 30 to 300 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	18.0 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
E band	60 to 90 GHz
W band	75 to 110 GHz
F band	90 to 140 GHz
D band	110 to 170 GHz
Y band	325 to 500 GHz

Comparison of radio band designation standards

Comparison of frequency band designations

Frequency		IEEE	EU, NATO, US ECM	ITU
				no.	abbr.
			A
3 Hz				1	ELF
30 Hz				2	SLF
300 Hz				3	ULF
3 kHz				4	VLF
30 kHz				5	LF
300 kHz				6	MF
3 MHz		HF		7	HF
30 MHz		VHF		8	VHF
250 MHz			B
300 MHz		UHF		9	UHF
500 MHz			C
1 GHz		L	D
2 GHz		S	E
3 GHz			F	10	SHF
4 GHz		C	G
6 GHz			H
8 GHz		X	I
10 GHz			J
12 GHz		Ku
18 GHz		K
20 GHz			K
27 GHz		Ka
30 GHz				11	EHF
40 GHz		V	L
60 GHz			M
75 GHz		W
100 GHz
110 GHz		mm
300 GHz				12	THF
3 THz