Hi
Sorry for long delay reply
The attenuation
parameter which is the most important at 100GHz
is the first oxygen line. The rate of attenuation
is about 0.8 dB per kilometer according to data
I have.
The max CW Tx power obtainable for commercial
devices is about 50milliwatts.
The likely receiver
sensitivity is about -67dBm for that bandwidth at
100GHz.
Antenna gain of course depends on size,
and that depends on the platform geometry you have
in mind.
Plug those figures into a one-way microwave
path analysis programme and you have the answer.