HORN ANTENNA

[Solving Means] A horn antenna according to an embodiment of the present technology includes: a waveguide portion; and a horn portion. The waveguide portion includes a first dielectric block and a first post wall, the first post wall including a plurality of conductive columnar bodies that passes through the first dielectric block and demarcating a first waveguide that extends in one axial direction. The horn portion includes a first widening portion that is connected to one end of the waveguide portion in the one axial direction. The first widening portion includes a second dielectric block that is thicker than the first dielectric block and a second post wall that includes a plurality of conductive columnar bodies and demarcates a second waveguide whose width increases as a distance from the first waveguide increases, the plurality of conductive columnar bodies passing through the second dielectric block.