Electronic – Matching oscilloscope impedance to detector

That's a relatively wide bandwidth to match a circuit over. The Bode-Fano equation governs bandwidth/return loss for reactive circuits, and google has some articles that will help with this. As long as the impedances you are working with don't vary much, you can do a decent job of matching. Resistive matches are pretty broadband, but lossy.

If you don't have access to a \$50 \Omega\$ feedthrough terminator, a T-connector with a \$50 \Omega\$ termination should work just as well. This was standard practice at my old company when we used external hall-effect current probes with our \$1 M\Omega\$ scopes.

(Aside: I personally prefer using external \$50 \Omega\$ terminators even if the scope supports \$50 \Omega\$: they're usually capable of handling more power, and if you accidentally hook up something incorrectly, at least you're blowing an inexpensive and easily-replaceable component vs. necessitating a potentially expensive scope repair!)