Patent ID: 6816030
Filing Date: 2004-11-09
Classification: H01P

Abstract:
An impedance matching circuit connected between an input circuit and an output circuit, the input circuit generating a target signal and an image signal associated with the target signal, the image signal being a heterodyne noise or a super-heterodyne noise of the target signal, the impedance matching circuit comprising:a circuit board comprising a metal membrane which functions as a ground layer for providing a reference ground voltage; a first microstrip circuit comprising a first microstrip line positioned on the circuit board and coupling with the metal membrane for forming a first transmission line structure, the first microstrip line comprising a first terminal and a second terminal, the first terminal connected to the input circuit, and the second terminal being an open circuit; a second microstrip circuit comprising a second microstrip line positioned on the circuit board and coupling with the metal membrane for forming a second transmission line structure, the second microstrip line comprising a first terminal and a second terminal, the first terminal being an open circuit, and the second terminal connected to the output circuit; and a third microstrip circuit comprising a third microstrip line with a third predetermined length positioned on the circuit board and coupling with the metal membrane for forming a third transmission line structure, the third microstrip line comprising a first terminal and a second terminal, the first terminal connected to either the first microstrip line or the second microstrip line, the second terminal being an open circuit, and the third predetermined length being determined according to a frequency of the image signal; wherein the first, second, and third microstrip lines are conductive bars, and when the target signal and the image signal are both inputted into the impedance matching circuit, the image signal will bypass through the third microstrip line toward the ground layer, and the first microstrip line couples with the second microstrip line to generate an electromagnetic coupling so as to pass the target signal from the first microstrip line to the second microstrip line and output the target signal to the output circuit.