3cm (10GHz)

This is an amateur band I have not really tried. 

Back in the 1970s, I made a Gunn diode oscillator and got a few feet. 

Some take it very seriously and run big dishes and high power. Some have used the band for EME QSOs. Others have played with it with wideband FM using Gunnplexers and similar oscillators. 

These days the equivalent to these are HB100 Doppler radar modules available for just over a pound.  I have not seen wideband FM transceivers built around these, but I am sure they exist. Some have even used these with a dish for ATV and achieved some astounding ranges.

See https://sites.google.com/view/g3xbm4/home/vhfuhfmicrowaves/homebrew/10ghz.