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There is confusion and controversy
about the microwave frequency band definitions used in North America.
Legend has it that the designators were originally contrived during
World War II to confuse the enemy. Engineers in Fort Monmouth New
Jersey came up with the letter codes, which were classified as Secret
at the time. Naturally, a logical progression of A, B, C wouldn't
do for that purpose, so they chose L, C, X and K, and a whole bunch
of lower-case letter sub-band designators that have been all but
forgotten, with the exception of the Ku and Ka bands. After the
war, Uncle Sam didn't declassify the system for everyone's use,
different companies such as Sperry, Motorola, Narda, Hewlett Packard
and Raytheon made educated guesses on the secret frequency bands,
with inconsistent results and little attempt to organize an industry-wide
In 1959 the world came to an
agreement on the designator letters, at the International Telecommunications
Union meeting in Geneva. The 1959 approved designators (Article
2, Section 11 of the Radio Regulations) are available in the ITT
Reference Data for Radio Engineers. At this point this data is obsolete,
perhaps because they never considered that anyone would be interested
in frequencies above 40 GHz. Kind of like when the phone company
standardized on seven digit phone numbers, thinking that one area
code for each U. S. state would provide enough phone numbers to
last forever. Thanks to this short sightedness, the misery of changing
area codes has become routine. But I digress...
In 1984, the IEEE microwave nerds
agreed on the standard letter-band designations shown in the table
below, the first two columns of which you should commit to memory
if you want to be taken seriously.
Standard Radar Frequency
Free Space (centimeters)
||1 to 2
||30.0 to 15.0
||2 to 4
||15 to 7.5
||4 to 8
||7.5 to 3.8
||8 to 12
||3.8 to 2.5
||12 to 18
||2.5 to 1.7
||18 to 27
||1.7 to 1.1
||27 to 40
||1.1 to 0.75
||40 to 75
||0.75 to 0.40
||75 to 110
||0.40 to 0.27
time for a Microwaves101 Rule of Thumb,
which we loosely apply to memory aids as well as other useful microwave
sound-bite info!! Want to remember the correct order of Ku, K and
Ka radar bands? K is the middle band (18-27 GHz), while Ku-band
is lower in frequency (think K-"under") and Ka-band is
higher in frequency (think K-"above").
The frequency band designator
story does not end with the IEEE, since United States waveguide
manufacturers have adopted their own set of standards over time,
corresponding to frequency passbands of the many different rectangular
waveguide cross-sections that have become standard in the industry
(waveguides behave like bandpass filters). Unlike the IEEE frequency
standards, there is considerable overlap among the waveguide bands,
so that you can choose the waveguide type where your application
is nearest the center frequency.
We keep our waveguide letter
band and dimensional info on another page (click
here). Although there are disagreements between waveguide vendors,
our table is representative of the US system (other countries such
as the U.K. have their own weird nomenclature that is just as confusing).
The material below just came
to our attention, it also speaks to the origin of the microwave
frequency letter bands, and it seems to make a good deal of sense.
|up to 200 MHz
|200 to 250 MHz
|250 to 500 MHz
||P for "previous",
as the British used the band for the earliest radars, but later
switched to higher frequencies.
|0.5 to 1.5 GHz
||L for "long"
|2 to 4 GHz
||S for "short"
wave. Don't confuse this with the short wave radio band, which
is much lower in frequency
|4 to 8 GHz
||C for "compromise"
between S and X band.
|8 to 12 GHz
||Used in WW II
for fire control, X for cross (as in crosshair)
|12 to 18 GHz
||Ku for "kurz-under".
|18 to 26 GHz
means short, yet another reference to short wavelength.
|26 to 4-0
||Ka for "kurz-above".
|40 to 75 GHz
||V for "very"
high frequency band (not to be confused with VHF)
|75 to 110 GHz
||W follows V
in the alphabet
EW letter bands
This came in from Andy, the EW
letter bands cannot be ignored! Caution, the information below came
from a Canadian
Note that the channel width is
not the full band. For example, an 18 GHz Band J radio would have
channel steps 1000 MHz apart (17,000-18,000-19,000...) Thanks to
||0 to 250
||250 to 500
||500 to 1,000
||1,000 to 2,000
||2,000 to 3,000
||3,000 to 4,000
||4,000 to 6,000
||6,000 to 8,000
||8,000 to 10,000
||10,000 to 20,000
||20,000 to 40,000
||40,000 to 60,000
||60,000 to 100,000
If anyone has any other information
on the frequency letter bands (such as a reference for these definitions),
send it in!