There are two quite separate systems for designating radar frequencies. The older one is based on wavelength and was originated during WW2. It goes as follows:

The original wavelength used for search radars was 23cm.  This became known as L-band (for Long).

When shorter wavelengths (10cm) were introduced, these became known, quite logically, as the S-band, S standing for Short.

When fire control radars (3cm wavelength) entered service they were designated the X-band radars - because X marks the spot.

It was then hoped that an intermediate wavelength would combine the advantages of both.  This was C-band (C = Compromise).

When the Germans decided to introduce short wavelength radars, they selected a frequency of 1.5 cms.  This became known as K-band (K = Kurtz, the German word for short).

Unfortunately, the Germans, with unparalleled Teutonic precision, had selected the one radar frequency that is absorbed by water vapor so the K-band radars don't work in rain or fog.  Postwar this was countered by selecting frequencies either just over K band (Ka or K-above) or just under it (Ku or K-under).

Finally, the first radars operated with meter-long wavelengths.  These were designated P-band (P standing for Previous).

This system was complex, clumsy and difficult to use.  Consequently it was replaced by a rationalized system based on frequency with the designations running from the A band to the P band.

      Old P-band = Modern A/B band
      Old L-band = Modern C/D-band
      Old S-band = Modern E/F band
      Old C-band = Modern G/H band
      Old X-band = Modern I/J band
      Old K-band = Modern K band
.

Back to the Naval Technical Board