Oscilloscopes like Rohde & Schwarz RTO,Keysight 6000 & S,Lecroy Wavepro HD and Tek MSO 6 bandwidths that go up to 6 - 8 GHz.That is seriously deep in the microwave range,impedance matching becomes extremly important and signal degradation due to impedance mismatch becomes very common.
Here are two important things to keep in mind : 1 All of the above mentioned scopes use BNC connectors,they might use fancy BNCs,they name it "precision BNC" but at the end of the day,its a BNC in 8 GHz rated instrument that is supposed to analyze signals in time domain.
2. VSWR... most scopes I named above dont provide specs in datasheet that shows VSWR vs frequency.One exception I found is RTO,the spec says under 2 GHz VSWR is 1.25 : 1 and above 4 GHz its 2.0 : 1.
I am not microwave wizard nor a milimeterwave warlock but... 2.0 : 1 VSWR!? Holy schmitt trigger that aint good! Thats catastrophically bad,it might not be such a big deal in spectrum analyser or antenna,but this is oscilloscope! We use them to look at time domain,we need decent time domain signal fidelity,strong reflections like that must wreak havoc on waveform shape if its anything other than steady sinewave.
Even in realistic 5 ENOB scenario,you can see the echoes down to 36 dbc,with 2.0 : 1 VSWR you have 11% of the signal reflected,it will the travel back toward DUT and cause all kinds of nasty schmitt inside there,get reflected again and arrive as delayed echo.This to me sounds like big big problem,maybe I am just noob and there is something that prevents this from being issue but I cant think of anything.
2.0 : 1 VSWR in oscilloscope... just think about it.And thats the 6 GHz RTO,imagine how its like in the 8 GHz BNC scopes like Keysight S,Wavepro HD or Tek MSO 6,they dont give any VSWR information in their datasheets.My point is,isnt a 8 GHz scope with BNC bullschmitt? Isnt 8 GHz BNC scope inherently faulty concept,isnt it stupid device that cant do its job properly at those high frequencies despite being advertised as 8 GHz? Isnt it waste of money? Isnt it practicaly essential to get non BNC scope,with proper microwave connectors to look at 6 - 8 GHz signals with good fidelity?