Abstract: A down-converter includes two low-noise amplifiers, a 90-degree hybrid coupler, two first matching circuits, and a down-converting circuit. The two low-noise amplifiers respectively amplify a first beacon signal and a second beacon signal to generate a first amplified signal and a second amplified signal. The 90-degree hybrid coupler includes two input ports and two output ports for transforming the first amplified signal and the second amplified signal into a first coupler output signal and a second coupler output signal. The two first matching circuits are respectively coupled to the two input ports or the two output ports of the 90-degree hybrid coupler and each first matching circuit has a first tuning mechanism disposed in one side of the first matching circuit and not contacting the first matching circuit. The down-converting circuit performs a frequency down-conversion on the first coupler output signal and the second coupler output signal.