I have a question regarding bandpass filter. What is unbalanced port and balanced ports? I noticed that outputs of balanced ports are connected to RF_P / RF_N of Zigbee IC. What are RF_P / RF_N?
A balanced port uses two connections. If it is an input, it expects the signal on RF_N to be the inverse of what is on RF_P. If it is an output then RF_N should be the inverse of RF_P.
Sending signals differentially is sensible because the net emission (EMI) from a balanced pair of signals is zero. There is also a benefit for the receiver, it can subtract one signal from the other to get 2x net signal and cancel out any common interference picked up on the two wires.
Balanced signalling has nothing specifically to do with any filter type.