Waveguide device, and antenna device including the waveguide device

A waveguide device comprising:

• an electrical conductor including an electrically conductive surface;
• a waveguide including an electrically-conductive waveguide surface opposed to the electrically conductive surface, and extending alongside the electrically conductive surface;
• and
• an artificial magnetic conductor extending on two sides of the waveguide;
• wherein
• the waveguide includes a first portion extending in one direction and at least two branches extending from one end of the first portion, the at least two branches including a second portion and a third portion that extend in mutually different directions;
• the waveguide defined by the electrically conductive surface, the waveguide surface, and the artificial magnetic conductor includes an enlarged gap portion at which a gap between the electrically conductive surface and the waveguide surface is locally enlarged;
• a size of the gap between the electrically conductive surface and the waveguide surface is greater at the enlarged gap portion than at any site on the waveguide that is adjacent to the enlarged gap portion, and is smaller than a distance between the electrically conductive surface and a root of the waveguide;
• and
• at least a portion of a junction at which the first portion is joined with the at least two branches of the waveguide overlaps the enlarged gap portion, as seen through in a direction perpendicular to the electrically conductive surface.