Abstract: A main line (transmission line) has a first end and a second end. A sub-line (transmission line) coupled to the main line has a third end and a fourth end. The main line and the sub-line are coupled to each other. A direction of the main line is identical to a direction of the sub-line. An unbalanced node is connected to the first end. The first balanced node is connected to the first end, and the second balanced node is connected to the fourth end. The second end and the third end are connected to a reference potential. A first LC resonant circuit is connected between the first balanced node and the unbalanced node, the second balanced node and the fourth end, or the first end and the unbalanced node.

Abstract: A main line (transmission line) having a first end and a second end. A sub-line (transmission line) coupled to the main line. An unbalanced signal is input to and output from an unbalanced node connected to the first end. A balanced signal is input to and output from a first balanced node and a second balanced node. The main line and the sub-line are coupled to each other. A direction of the main line is identical to a direction of the sub-line. The second end and the third end are connected to a reference potential. The first balanced node and the second balanced node are connected to the unbalanced node and the fourth end, respectively. A first LC resonant circuit is connected between the second end and the reference potential or the third end and the reference potential.

Abstract: A first transmission line transformer receives and outputs an unbalanced signal and performs impedance transformation. A second transmission line transformer performs unbalanced-to-balanced transformation. The first transmission line transformer includes a first main line and a first sub-line. The direction of the first main line is identical to the direction of the first sub-line. An end of the first sub-line is grounded. An end of the first main line is coupled to the unbalanced-signal input/output node. The second transmission line transformer includes a second main line and a second sub-line. The direction of the second main line is identical to a direction of the second sub-line. An end of the second main line and the second sub-line are grounded. An end of the second main line and the second sub-line are coupled to the balanced-signal input/output nodes.

Abstract: A first primary line has a first node at one end and a third node at another end and transmits a radio-frequency signal between the first node and the third node. A second primary line has a second node at one end and a fourth node at another end and transmits a radio-frequency signal between the second node and the fourth node. A first secondary line has a portion connected to the second node and is electromagnetically coupled to the first primary line. The second secondary line has a portion connected to the first node and has another end connected to a portion of the first secondary line. The second secondary line is electromagnetically coupled to the second primary line. A first capacitor is connected in parallel to a portion of the second primary line or a portion of the second secondary line.