Waveguide

A waveguide comprising:

• a first waveguide having a first waveguide hole;
• and
• a second waveguide having a second waveguide hole and assembled to the first waveguide with a predetermined gap between the first waveguide and the second waveguide, wherein
• the first waveguide and the second waveguide are assembled in a state capable of transmitting an electromagnetic wave through the first waveguide hole and the second waveguide hole,
• the second waveguide hole has an opening on one surface of the second waveguide facing the first waveguide, and the opening has a rounded polygonal shape or a circular shape,
• the second waveguide includes a resin molded product and a metal coating film covering the resin molded product, and the second waveguide has a choke groove around the second waveguide hole, and
• the choke groove has such a shape that a length between a wall surface of the second waveguide hole and an inner wall surface of the choke groove adjacent to the second waveguide hole is constant along a circumferential direction of the second waveguide hole,
• the second waveguide has a recessed portion in a portion on the one surface located across the choke groove from the second waveguide hole, and
• a portion inside the recessed portion is a protruding portion.