Why Do RF Band Definitions Overlap?

RF band definitions overlap because they belong to different naming systems, not one universal set of non-overlapping frequency ranges. UHF and SHF classify broad frequency intervals; radar letter bands and satellite band names use different boundaries. The same frequency can therefore have more than one valid label. ITU-R V.431-9 Note 5 explicitly warns that letter designations do not have a single standard correspondence to frequency bands. [1]

How One Frequency Can Be Both UHF and S-Band

In ITU-R V.431-9 Table 1, ultra high frequency (UHF) covers frequencies above 300 MHz through 3 GHz. The radar S-band range listed in Table 4 is 2–4 GHz. Thus, 2.4 GHz is both UHF and radar S-band: the labels describe the same frequency under different classifications, not two different signals. Their shared interval extends from 2 to 3 GHz, a calculated width of 3 − 2 = 1 GHz. [1]

That does not mean UHF and super high frequency (SHF) overlap within Table 1. Its lower limits are exclusive and upper limits inclusive: exactly 3 GHz belongs to UHF, while SHF begins above 3 GHz. This endpoint rule applies to that table; it should not be assumed for every letter-band chart. [1]

Why Satellite Ku-Band Crosses the Radar X/Ku Boundary

The radar ranges listed in ITU-R V.431-9 Table 4 place X-band at 8–12 GHz and Ku-band at 12–18 GHz. In contrast, 47 CFR §25.103 defines the U.S. conventional Ku-band downlink as 11.7–12.2 GHz. That satellite interval straddles the 12 GHz radar boundary. A frequency below 12 GHz can therefore be part of a conventional Ku downlink while lying within the listed radar X-band range. Neither label is necessarily wrong; the references serve different purposes. [1] [2]

These are interval calculations: subtract the lower edge from the upper edge and multiply by 1,000 to convert GHz to MHz. The portion below 12 GHz is 300/500 = 60% of the defined downlink span. This percentage describes neither traffic nor usable terminal bandwidth. The single point at 12 GHz contributes no width to the calculation. [1] [2]

Why K/Ka Boundaries Differ Between References

ESA’s satellite frequency overview lists K-band as 18–26 GHz and Ka-band as 26–40 GHz. The radar ranges in ITU-R V.431-9 Table 4 use 18–27 GHz for K and 27–40 GHz for Ka. At 26.5 GHz, ESA’s overview gives Ka, while the listed radar range gives K. This is a difference between references, not evidence that a frequency boundary has changed over time. ESA’s overview is not a substitute for the naming reference specified in a radar contract. [3] [1]

The naming difference also explains the 20 GHz example: it lies within the listed radar K range of 18–27 GHz and the U.S. conventional Ka downlink interval of 19.7–20.2 GHz. ITU Table 4 notes that K and Ka are often grouped under the single symbol Ka in space radiocommunications. Calling a downlink “Ka-band” therefore does not make it radar Ka-band. [1] [2]

A Worked Specification Check: Use Frequencies, Not Just Letters

Consider an illustrative ground-terminal requirement to cover the full U.S. conventional Ku receive/transmit pair. A request saying only “Ku-band” leaves both the naming reference and the signal direction unclear. A more useful specification is:

Receive: 11.7–12.2 GHz. Transmit: 14.0–14.5 GHz. Naming reference: conventional Ku as defined in 47 CFR §25.103. [2]

Now assume a candidate component’s datasheet specifies an operating range of 12–18 GHz and labels it Ku-band. That range does not cover the required 11.7–12.0 GHz receive portion: the missing span is (12.0 − 11.7) × 1,000 = 300 MHz, or 60% of the 500 MHz receive requirement. Matching the word “Ku” would miss this gap. This is a hypothetical range-coverage check, not a test result or the rating of a particular product.

For an antenna feed network, record those receive/transmit edges alongside polarization, port layout, and interfaces. A waveguide diplexer separates frequency paths, whereas an orthomode transducer separates orthogonal polarization paths. A waveguide-to-coaxial adapter also requires the intended waveguide, flange, and connector details. The band name alone specifies none of these interfaces.

Exact frequencies resolve the naming ambiguity; they do not remove the overlap between definitions or prove hardware performance. Likewise, a band label is not an operating authorization. The U.S. service definitions in §25.103 and the Table of Frequency Allocations in §2.106 are separate references; the example above is not a worldwide permission to transmit. [2] [4]