A harmonic filter for filtering a plurality of frequency components from an input signal comprises a phase shifter for generating an in-phase signal and a quadrature-phase signal according to the input signal; and a plurality of polyphase filter networks coupled in series. The first polyphase filter network in the series is coupled to the phase shifter for receiving the in-phase and quadrature-phase signals. Each polyphase filter network is for filtering a corresponding one of the frequency components from the input signal.