What mixer must be used to measure IF of ~1GHz

[Terminator3]

From widely available on internet article SayreCh07 "CHAPTER 7 Mixer Design":

However, the IF must be no higher in frequency than 50 MHz or so,
since the difference between the LO and RF frequencies must be relatively small due to
the mixer’s resonant distributed design,

so, have doubts

 

[BigBoss]

He talks about resonating mixers.These mixers have IF output that is dedicated to a certain frequency.( Distributed Design, resonating output)