Confused about anti-aliasing in analog filters
Aliasing does not happen in the analog world. It only happens when you sample a signal.

If you have an ADC with sampling frequency $f_s$, then you'll have aliasing if the input signal has frequency components larger than $f_N=f_s/2$. To avoid aliasing, it's common to low-pass filter the signal before it is input into the ADC. That way, you make sure that the digital signal out of the ADC has no aliasing.

Such an analog filter is called an "anti-alias filter", not because it will experience anything related to aliasing itself, but because its purpose is to avoid aliasing in the ADC.