Following are the microwave bands : (a) X (b) ku (c) V (d) Q Arrange these in the order of increasing frequency :
(a), (b), (d), (c)
Place each band on the frequency scale and the order follows.
| Band | Frequency | Typical use |
|---|---|---|
| X | 8 – 12 GHz | Radar, military satellite links |
| Ku | 12 – 18 GHz | Direct-to-home television, VSAT |
| K | 18 – 27 GHz | — |
| Ka | 27 – 40 GHz | High-throughput satellite |
| Q | 33 – 50 GHz | Radio astronomy, millimetre links |
| V | 40 – 75 GHz | Short-range gigabit radio, 60 GHz WiGig |
Increasing frequency: X → Ku → Q → V, that is (a), (b), (d), (c) — option 4.
The two traps are the letters themselves. First, the sequence is not alphabetical — the letters are wartime code names, and the microwave order runs L, S, C, X, Ku, K, Ka, Q, U, V, W. Second, Q and V look interchangeable to anyone who has not learned the millimetre-band letters, and they overlap between 40 and 50 GHz; Q starts lower, at 33 GHz, so it precedes V.
"Ku" means K-under — the band immediately below K — while Ka means K-above. Getting that pair the wrong way round is the commonest error in questions of this type, and it is what option 1 is built on.
Why the millimetre bands are used at all, given that loss climbs steeply with frequency. Two reasons: the enormous bandwidth available — a 2 GHz-wide channel is unremarkable at 60 GHz and impossible at 2 GHz — and, for V band specifically, the oxygen absorption peak near 60 GHz. Absorption of about 15 dB per kilometre confines the signal to a short range, which is a defect for a long link but a virtue for dense short-range reuse: the same channel can be used again a few hundred metres away without interference.
Antenna size scales the other way, which is the other attraction: for a given gain, \(A_{e}=\dfrac{G\lambda^{2}}{4\pi}\), so a V-band antenna is tiny compared with an X-band one of the same gain — the reason 60 GHz radios fit inside a laptop.
Hence, the increasing order is (a), (b), (d), (c).
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