A frequency tripler includes a double-frequency in-phase signal generator, a double-frequency quadrature signal generator and a mixer. The double-frequency in-phase signal generator is arranged for receiving at least an in-phase signal and a quadrature signal to generate a double-frequency in-phase signal whose frequency is twice that of the in-phase signal or the quadrature signal; the double-frequency quadrature signal generator is arranged for receiving at least the in-phase signal and the quadrature signal to generate a double-frequency quadrature signal whose frequency is twice that of the in-phase signal or the quadrature signal; and the mixer is arranged for receiving the in-phase signal, the quadrature signal, the double-frequency in-phase signal and the double-frequency quadrature signal to generate an output signal whose frequency is triple that of the in-phase signal or the quadrature signal.