Radio Navigation: choice of frequency

[Kriekos]

Hi everyone,

​​​​​​Below you will find a (homemade) summary on the frequencies used in all sorts radio navigation equipment. My question: what is the reason for some being much higher frequency than others?
For example: ILS LOC is VHF and ILS GS is UHF. But UHF requires more power than VHF (power is proportional to frequency) and UHF is attenuated more than VHF (attenuation of a space wave is proportional to frequency). So I don't see a point for choosing a higher frequency. Same with for example WX radar: why choose such a high frequency? Why not use a frequency as low as possible? I have spent a lot of time making sense of refraction and attenuation theory and types of waves, but none of it explains the choice for frequencies like UHF and SHF.

Thanks in advance!

https://cimg0.ibsrv.net/gimg/pprune.org-vbulletin/901x474/screenshot_2023_02_07_12_03_40_89_ab7988c7b00b15bc78ec5a428c 58236f_ad5227d4ff053723c741c19ca1e3f5e272c97c04.jpg

[paco]

Weather radar is tuned to the size of large raindrops (3 cm) so the frequency is governed by the wavelength required (divide the speed of light by one or the other).

VHF does not provide the bandwidth required for the short pulses that allow good target definition, so SHF bands are currently used. Thus, radar is limited to line of sight.

The leading edge of the pulse must be sharp, so it must jump to its maximum value suddenly. This is a serious matter with longer waves, because radio waves with different frequencies have to be mixed, so the process is better done with very short (centimetric) waves.

You also need to prevent navaids interfering with each other so a particular range will be needed, again, based on frequency and hence wavelength.