Patent ID: 6975186

Claim:
A filter circuit characterized by comprising: a dielectric board; a first conductor pattern formed as a distributed line pattern in the dielectric board and having one end grounded and the other end opened, the first conductor pattern having high-frequency signals inputted thereto; a second conductor pattern formed as a distributed line pattern parallel to the first conductor pattern in the dielectric board and having one end grounded and the other end opened, the second conductor pattern being electromagnetically coupled with the first conductor pattern and thus outputting a high-frequency signal of a predetermined frequency band selected from the high-frequency signals inputted to the first conductor pattern; a third conductor pattern formed as a distributed line pattern parallel to the first conductor pattern and the second conductor pattern in the dielectric board and having both ends opened; and a first capacitor and a second capacitor for adding parallel capacitance based on a concentrated constant to the first conductor pattern and the second conductor pattern; wherein as each of the first to third conductor patterns is formed with a length shorter than λ/4 with respect to a passing wavelength λ, inductive electromagnetic coupling is carried out between the first conductor pattern and the second conductor pattern, and capacitive electromagnetic coupling is carried out between the first and second conductor patterns and the third conductor pattern.