Variable-frequency LC filter, high-frequency frontend module, and communication apparatus

A variable-frequency LC filter comprising:

• an input terminal;
• an output terminal;
• a first series arm LC filter circuit comprising a first inductor and connected between the input terminal and the output terminal;
• a first parallel arm LC filter circuit comprising a second inductor and a first variable capacitor, the first parallel arm LC filter circuit being connected between ground and a node between the input terminal and the first series arm LC filter circuit;
• and
• a second parallel arm LC filter circuit comprising a third inductor and a second variable capacitor, the second parallel arm LC filter circuit being connected between ground and a node between the output terminal and the first series arm LC filter circuit, wherein:
• the input terminal, the output terminal, the first series arm LC filter circuit, the first parallel arm LC filter circuit, and the second parallel arm LC filter circuit are mounted on a principal surface of a substrate,
• the second parallel arm LC filter circuit is directly connected to the first inductor, and
• the first variable capacitor and the second variable capacitor are disposed on the principal surface in an arrangement such that a strength of a magnetic field coupling between the first inductor and the third inductor is greater than a strength of a magnetic field coupling between the second inductor and the first inductor, and is greater than a strength of a magnetic field coupling between the second inductor and the third inductor.