I see Kirt has given you a very comprehensive
answer under "components".
Not much to add to
that. I guess the coupler of 1960s vintage has N
type connectors, which at that time maxed out at
6 or 7GHz, so that probably sets a top limit to
the frequency range. Above 7GHz the N-type connector
starts to launch waveguide modes and the Reflexion
Coefficient vs frequency becomes erratic (although
today technology has improved that to around 12GHz).
The only point to be careful about then is obtain
a good quality APC-7 to N type transition for at
least 2 of the 3 exposed ports of the coupler.
Good luck with that.
At bottom, life is all
Sucking in and blowing out.