Polyphase filter inputs are always quadrature components tha come from a mixer or LO signal source ( divided by 2 ) etc..
I means IN-PHASE
Q means QUADRATURE-PHASE.
First order filter has a single sided pole that is determined by
Fp=1/2*pi*R*C
Second order has two independent single sided poles etc..
Because of single sided poles, spectrum is NOT symmetrical but single sided..
There are lot of information about polyhase filters but I have no time to explain..