Almost all of the microwave test equipment I've ever seen and used has N connectors, with exception of some scopes that use either custom fancy BNCs (keysight does/used to do this)) or SMA.
Exceptions that I know of are VNAs which seem to use special connectors (but the ones I've used are also rated up to 110 GHz and used 1mm-based connectors).
Of course, there is nothing wrong with the N connector – in fact I like it, it feels rugged and like it can take a good bit of use (is this the reason?).
However, every single occasion I've worked with the instruments, or seen someone work with them, the first thing they do is put on a N-to-SMA (or 3.4mm or 2.4mm) adapter. So why not just put those connectors on the equipment in the first place? Is it really just the ruggedness, some other reason I'm missing, or is this some silly "because it used to be that way and nobody likes change"?
Best Answer
Two Reasons: Pout and S11.
N connectors have a large surface contact area for >1A power levels or >10dB and large diameter means better "potential return loss over a wide GHz range is possible with machining tolerances of 0.1% affecting this.
However SMA is more common for low power apps but quality varies with undocumented suppliers. (greatly and not gauranteed)
But never try to pump >>1 Amp thru 1u" flash gold plated SMA connector (crap...