Patent ID: 7439831

Claim:
A transition circuit converting the transmission path of a microwave in a direction either from a waveguide to a microwave transmission line or from a microwave transmission line to a waveguide, said transition circuit comprising: a waveguide having a notched portion formed by cutting away a portion of the wall of the waveguide from the end portion thereof; a dielectric substrate in which a portion extending outside the waveguide through the notched portion of the waveguide is formed, the substrate being coupled to the end portion of the waveguide; a plurality of polygonal conductor patterns formed regularly disposed on the face of the dielectric substrate, which is opposed to the interior of the waveguide; a ground conductor formed on the other face of the dielectric substrate; an electrically connecting portion electrically connecting the ground conductor and each of the conductor patterns; an open stub formed flush with the conductor patterns formed on the dielectric substrate; and a conductor line portion of a microwave transmission line, which is formed on the portion of the dielectric substrate that extends outside the waveguide, the conductor line portion being electrically connected to the open stub.