To maintain a wide bandwidth, flat-response measurement, thecoaxial cable impedance must match at least the power supply impedanceor the oscilloscope input impedance.

Furthermore, they can severely load the DUT as the oscilloscope’s input impedance is not significantly higher than the circuit’s output impedance. Active probes Single-ended Active probes do not use ...

Why is this? Crucial to the operation of an oscilloscope is a very high input impedance, to minimise current draw on the circuit it is investigating.

This path together with the oscilloscope’s input impedance acts as a low-pass filter, and again, it’s necessary to align the poles of the high- and low-pass filters to obtain a flat response.