PURPOSE: To reduce the deviation of the matching in a high frequency band by adding a capacitive circuit to a microstrip line.

CONSTITUTION: A radio wave propagated through the microstrip line 2, as shown in the Smith chart, goes from a point A to a point B by the inductance component of a gold wire 4, goes to a point C from the point B by the capacitive component of a pin diode 3, goes to a point D from the point C by the inductive component of the gold wire 4, returns to a point E from the point D by a capacitive stub 5 to form a matching circuit. That is, as the frequency goes higher, since the inductance component of the wire 4 is increased, the rotation from point A → point B → point C → point D is eminent and the impedance resides in the point D finally to make the deviation in the matching eminent. Through the constitution above, since the stub 5 is added, the rotation from the point D to the point E allows the matching of circuit even with the dispersion in the capacitance of the diode 3 or the inductive component of the wire 4.