Abstract: It is an object of the present invention to realize a low-pass filter that has an increased number of stages of filter elements and can obtain a large combined capacitance with a simple configuration of a plane circuit, can set an attenuation pole in the vicinity of a pass band and has a steep out-of band attenuation characteristic. In order to attain such an object, three or more top end open stubs, which are set to have a large electric length in a range in which a length of is shorter than ¼ of a wavelength of a pass frequency, are disposed substantially in parallel so that their respective open ends face an identical direction to thereby form a combined line, and a high impedance line that is shorter than the wavelength of the pass frequency is connected to at least one part among parts between neighboring ends on the opposite side of open ends of the top end open stubs.

Abstract: It is an object of the present invention to realize a low-pass filter that has an increased number of stages of filter elements and can obtain a large combined capacitance with a simple configuration of a plane circuit, can set an attenuation pole in the vicinity of a pass band and has a steep out-of band attenuation characteristic. In order to attain such an object, three or more top end open stubs, which are set to have a large electric length in a range in which a length of is shorter than ¼ of a wavelength of a pass frequency, are disposed substantially in parallel so that their respective open ends face an identical direction to thereby form a combined line, and a high impedance line that is shorter than the wavelength of the pass frequency is connected to at least one part among parts between neighboring ends on the opposite side of open ends of the top end open stubs.