[Argus25]

One practical problem is the impedance of the medium or system that the attenuator is working in.

For low impedance mediums such as 50 or 75R ,even for heavy levels of attenuation like 20dB the attenuator can simply be comprised of resistors and no reactive elements.

The typical attenuators you see for this that plug in series with coaxial cables with a male & female BNC are designed with resistors only and are a design called a "ladder attenuator" When you drop them in series with the coax or transmission line, they don't create an impedance bump because they are 50R in and 50R out as one example and they have a very wide bandwidth from DC into the UHF region often if they are well made.

However, all the rules for attenuators change when you go to a higher impedance medium, such as a 1meg input on a scope that also looks like 1M with a 15pF capacitance across it. For high levels of attentuation, while still maintaining a high input impedance the input capacitance has a severe LPF effect.

So for example with a x10 scope probe which essentially needs about a series 9 Meg resistor, the severe HF roll off has to be corrected by putting a small parallel capacitor across the 9M resistor to maintain the HF response through the attenuator.

So all of a sudden for any reasonable bandwidth your attenuator now requires a reactive element to work properly, but it didn't in the lower impedance medium where the effects of parallel and stray capacitance are minimized.