To provide a polar type pass filter that is miniaturized and has a small relative band.
One line 1 of double winding helical lines 9A is connected to an entrance coaxial connector 10 and an exit coaxial connector 11. Serial resonators 15, 15 are respectively connected to both ends of the other line 2 of the lines 9A. Both the resonators 15, 15 consist of two helical lines 21, 21 and a capacitance C connected between a connecting point of both the lines and ground. Both the resonators 15, 15 act as a circuit equivalent to an open stub having quarter wavelength. The characteristic impedance of the open stub is as high as 9,500 ohms, and the filter indicates a narrow band characteristic of a relative band of 0.75% at a frequency 800 MHz.
Next Patent: LOW PASS FILTER