The first electromagnetic wave length used for search radar was 23cm, which was defined as L-band (the prefix of English long). Later, the central wave length of this band became 22cm. When an electromagnetic wave with a wavelength of 10cm is used, its band is defined as S band (the prefix of English short means an electromagnetic wave shorter than the original wavelength).
After the emergence of fire control radar which mainly uses 3cm electromagnetic wave, the electromagnetic wave with 3cm wavelength is called X-band, because X represents a point on the coordinate.
In order to combine the advantages of X-band and S-band, radars with a central wavelength of 5cm gradually appear, which is called C-band (C is the prefix of the word "combination" in English).
After the British, the Germans also began to develop their own radar independently. They chose 1.5cm as the central wavelength of their radar. This wavelength of electromagnetic wave is called K-band (k = Kurz, German prefix for "short").
Unfortunately, the wavelength chosen by the Germans with the unique "accuracy" of their Germanic nation can be strongly absorbed by water vapor. As a result, this band of radar can not be used in rain and foggy weather. In order to avoid this absorption peak, the radar designed after the war usually uses Ka band (KA, the abbreviation of English k-above, which means above the K-band) and Ku band (Ku, the abbreviation of English k-under, which means below the K-band) with a frequency slightly higher than the K-band.
Finally, because the earliest radar used meter wave, this band is called P band (P is the abbreviation of previous, that is, the prefix of "past" in English).
The system is very cumbersome and inconvenient to use. Finally, it was replaced by a wavelength division system divided by the actual wavelength. The conversion of the two systems is as follows.
Original P-band = current a / b-band
Original L-band = current C / d-band
Original S-band = current E / F-band
Original C-band = current g / h-band
Original X-band = current I / J-band
Original K-band = current K-band