They are named slices of the radio spectrum; lower bands pass through rain easily, higher bands carry more data but fade in heavy rain.
Satellite radios use microwaves, and engineers divide them into bands with letter names. Each band suits different jobs. NASA lists the ranges like this:
Below these sit VHF and UHF. NASA says the bands most often considered for small satellites are UHF, S, X and Ka.
NASA says the move to higher bands has been driven by the need for higher data rates, because higher frequencies and wider bandwidths can carry more. The cost is weather: at higher frequencies, rain fade becomes a significant problem.
That matters in India. A Ka-band link is fast, but a heavy monsoon shower between the dish and the satellite can weaken it.
Worked example: wavelength = speed of light ÷ frequency. An S-band signal at 2.5 GHz has a wavelength of 12 cm; a Ka-band signal at 30 GHz is only 1 cm long. Shorter waves are absorbed and scattered more by rain, and NASA notes they also form narrower beams that must be pointed more carefully.
Two transmitters on the same frequency, aimed at the same place, jam each other. So the use of each band must be licensed. NASA notes that heavy use of the bands up to S-band has crowded them and made licences harder to get.
Find NVS-01 and NVS-02 in the satellite list: they broadcast in the L1, L5 and S bands, and L1 is the band widely used by civilian receivers. Open the NavIC tracker
Frequency f and wavelength λ are linked by λ = c ÷ f, with c ≈ 3 × 10⁸ m/s.
Why rain matters more at Ka. Raindrops are a few millimetres across. When the wavelength shrinks towards the size of the drops, the drops absorb and scatter much more of the wave. At 20 cm (L-band) a raindrop is tiny compared with the wave; at 1 cm (Ka-band) it is not. This is the physical reason behind NASA's statement that atmospheric and rain attenuation grow at higher frequencies.
Why higher bands carry more data. A channel's capacity (Shannon) is
C = B × log₂(1 + S/N)
where B is bandwidth. A fixed fraction of a higher carrier frequency is a wider absolute bandwidth: 5 percent of 30 GHz is 1.5 GHz, while 5 percent of 2.5 GHz is only 125 MHz — twelve times less room.
Why higher bands give narrower beams. A dish of diameter D has a beamwidth roughly proportional to λ ÷ D. Going from 12 cm (S) to 1 cm (Ka) narrows the beam about twelve times for the same dish, as NASA notes. Narrow beams concentrate power (good for data rate) but must be pointed precisely — which ties frequency choice back to attitude control.
Ka-band waves are about a centimetre long, close to raindrop size, so rain absorbs and scatters them strongly; C-band waves are several centimetres long and pass through rain much better.
The second-generation NVS satellites transmit navigation signals in the L1, L5 and S bands; the L1 band is new with this series.
λ = c ÷ f = 3 × 10⁸ ÷ 12 × 10⁹ = 0.025 m, i.e. 2.5 cm.