If you try to correlate microwave letter designation and frequency ranges, don't bother thinking it should surely be systematic. Like Topsy, the letters just grew, and there's how it happened.
Reprinted from the May 1966 issue of EDN: The Electronic Engineer's Design Magazine under the name The Microwave Alphabet Soup, by James A. Rose, Western Editor.
Letter designations for microwave frequency bands are casually used by engineers closely associated with the microwave discipline. Out of curiosity, the uninitiated might consult a handy reference to ascertain the frequency associated with the letter designation. If he consults one reference book, there is no problem, but if he cross-checks references, he will discover he has opened the Pandora’s box. They just don’t agree.
There are a number of different versions of the story of telling how it all came about, but one that consistently arises seems to be valid. During World War II the frequency of microwave devices was considered classified information and a Signal Laboratory located at Ft Monmouth, N.J. assigned letter designations for frquency bands.
This provided a convenient means to discuss the equipment while concealing the classified numbers to which the bands referred. There was, thus, a deliberate effort to avoid sequential coherence in the letter chosen.
The radar designers, to a degree, were independent of the communication designers, and the bands of particular concern to them did not coincide logically with those used for communication purposes. Because letter designations were assigned independently by both groups, there was considerable disparity, even duplication of letters. The meaning of letters from one group was far removed from the meanings of the same letters to the other. It was a logical way to maintain secret information.
Because of frequent use of the letter designations, manufacturers of components and subassemblies began making educated guesses as to the frequency range that each letter signified. Often the guesses were incorrect and the incorrect guesses became part of the general system. This further added to the confusion.
After the war, competition among manufacturers led to a division of the spectrum into finer ranges for optimum design of particular devices. New letter designations were assigned, again without extensive intercompany standardization.
In an attempt to clear up some of the confusion, many companies published their educated guesses and, although incorrect, they became handy references to certain parts of the industry. Because electronic engineers frequently move from one company to another they often brought their pet references with them to their new jobs and wrote the definitions into their specifications.
A good example is NASA, which refers to its UHF link and its S band link. By NASA’s definition, UHF runs from 300 MC to 3,000 Mc and S band runs from 1,500 Mc to 5,000 Mc, which gives a nice 1,500 Mc overlap.
Most companies that work in the microwave discipline recognize the problem and are attempting to alleviate, if not solve it. Some companies have abandoned the letter designations completely and, omitting any reference to letter designation for bands, specify only frequency.
Other companies attempt to bridge the gap by retaining the common letter designations, but also immediately define the frequency limits. Often the letter designations are prefixed with company letter designations to qualify the source. Some companies have even offered to abandon some designations that are peculiar to them in return for abandonment of designations by others.
These moves have, as yet, borne little fruit, but hopefully changes will come about in the future. Until then, EDN presents a convenient list for your edification and confusion.
Microwave Bands (Gc)
ics & Nu-
|DBW 90-140||LS 1.7-2.6||Ke 12.4-15.35|
|DBA 60-90||XN 5.4-8.2||Kr 24.5-26|
For IEEE standard and ARRL letter-band designators, see Bands - 50MHz & Up