I have a quite basic question, after starting to re-read some RF theory. If a voltage source has a resistance of 50 ohms, and the equivalent impedance of a connected bandpass filter and its load are 50 ohms for a perfect match, won't there be significant loss - so much so that the passband will disappear entirely? If the bandwidth of a filter is defined as the portion where the gain is above 1/sqrt2 ~ 0.707 V, and the highest the output can ever get is 0.5 V due to the voltage divider rule, is it impossible to have an impedance matched band pass filter? Why would someone want to have a matched preselection filter between an antenna and an LNA if matching losses might cause the weak signal to be out of amplification range?
There are various methods to design "matched filters".
Most filters reject/reflect the undesired frequencies, and there needs to be a method (back at the signal source) to absorb the reflected energy.
Note the need to absorb-energy will set the attenuation-floor achievable.