There are three general purpose microwave tubes. The first is ordinary gridded tube, having electrodes like vacuum tube diode and triodes. The second type are those in which interaction between the electron beam and RF field takes place. The klystron is the example of the second type of microwave tubes. The third category of the device is one in which interaction between an RF field and electron beam is continuous. TWT (Travelling Wave Tube) is the example of this category.
The frequency of 'K' band is approximately in the range of :
26 - 32 GHz
The four options are the four bands in ascending order, and the last is the one meant for K. Read as a set, option 1 is C band, option 2 is X band and option 3 is Ku band; the remaining option is the answer — option 4.
| Band | IEEE range | Typical use |
|---|---|---|
| L | 1 – 2 GHz | GPS, mobile satellite |
| S | 2 – 4 GHz | Weather radar, Wi-Fi |
| C | 4 – 8 GHz | Satellite downlinks — option 1 |
| X | 8 – 12 GHz | Radar, military links — option 2 |
| Ku | 12 – 18 GHz | Direct-to-home TV, VSAT — option 3 |
| K | 18 – 27 GHz | Short-haul, radar |
| Ka | 27 – 40 GHz | High-throughput satellite |
A caution about the printed range. The modern IEEE designation puts K band at roughly 18 to 27 GHz, so none of the four options states it exactly; option 4's 26–32 GHz overlaps only its top edge and strays into Ka. Older band tables were looser — some pre-1970 schemes gave K band as broadly as 10.9 to 36 GHz, which would comfortably contain the printed figures — and the examiner has evidently used one of these. The answer is therefore flagged for confirmation against the official key.
The naming is what trips candidates up. The letters are historical wartime code names and are not alphabetical: the order runs L, S, C, X, Ku, K, Ka. "Ku" means K-under, the band just below K, and "Ka" means K-above. So Ku is always lower in frequency than K, and Ka always higher — which is exactly the relationship options 3 and 4 straddle.
Why K band itself is used sparingly : the water-vapour absorption line at 22.2 GHz sits squarely inside it, so atmospheric attenuation peaks there. Designers generally work either below it in Ku or above it in Ka, avoiding the absorption peak — one reason the band's boundaries are quoted so inconsistently across textbooks.
Hence, per the option set the answer is 26 - 32 GHz, the standard IEEE K band being 18 to 27 GHz.
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