FLAT ANTENNA

PROBLEM TO BE SOLVED: To provide a flat antenna that has a power supply structure by a waveguide, is good in productivity, and is capable of easily obtaining excellent characteristics.SOLUTION: The flat antenna includes a flat antenna body 2 having a flat plate shape and a radiation surface formed to radiate an electromagnetic wave, and an antenna power supply structure portion 6 for supplying electric power to the flat antenna body. Further, the flat antenna has a transmission line structure including a waveguide member 3 where a part of a waveguide structure portion 4 having an electrically conductive inner wall surface is formed, and a power supply plate 10 for forming a waveguide structure in combination with the part of the waveguide structure portion. By combining the waveguide member and the power supply plate, a configuration of the waveguide structure constituting a transmission line and an alignment of the waveguide structure with respect to the antenna power supply structure portion can be performed simultaneously, so that the waveguide structure can be easily matched with the antenna power supply structure portion with high precision.