PURPOSE: To put unnecessary resonance due to a high-order mode wave out of an in-use band by providing low-impedance parts where bosses are provided and low-impedance parts where a waveguide is reduced in height alternately.
CONSTITUTION: Low-impedance parts 3 where bosses 2 are provided and low- impedance parts 5 where the waveguide 1 is reduced in height are provided alternately. Low-impedance parts 5 pass only the basic mode wave and cut off the high-order mode wave, so the generated high-order mode wave causes resonance at a frequency depending upon the length l of the low-impedance part 5 shorter than the overall length of the filter in a radio-wave propagation direction. This resonance frequency is sufficiently high, so the unnecessary resonance by the high-order mode wave is put out of the passing band.
TAKEDA FUMIO
ISHIDA OSAMI
