Patent ID: 7671707

Claim:
A bandstop filter comprising: a main line connecting an input terminal and an output terminal to each other; and a ¼ wavelength resonator arranged in proximity to the main line approximately parallel to the main line with a distance of an approximately ¼ wavelength, wherein the ¼ wavelength resonator has a construction, in which means for short-circuiting with an earth conductor is provided at one end of the ¼ wavelength resonator and an open end is provided at the other end of the ¼ wavelength resonator, includes a first impedance non-continuous structure portion that divides a line section that is approximately parallel to the main line into portions, and in the line section that is approximately parallel to the main line, a characteristic impedance in a line section on the open end side is set higher than a characteristic impedance in a line section on the short-circuiting means side.