Re: 3.5GHz
I am equally baffled about the enthusiasm for ever higher frequencies into the GHz regions. Quite apart from the increasing "line of sight" characteristic there is also the point that for a portable transmitter to generate "x" mW of output power at 3.5 GHz requires a lot more primary power than one generating the same x mW at 800 MHz, and for primary power read "current from a small battery". On top of which the path loss over the same route (not the same as being "line of sight") is greater at 3.5 GHz than at 800 MHz and so on; I cannot be bothered to work it out but an additional loss in the region of 10 - 12 dB seems likely. As the result the maximum distance between cell and phone shrinks alarmingly.
I suppose all this "expansion" is to satisfy the burgeoning demand for mobile data rather than simple phone calls and texts, but I cannot get away from the thought that this "demand" is little more than an addict's craving for their next fix rather than anything really essential.