The present application discloses a coaxial dual-band antenna, including a waveguide tube, a ring groove, a high frequency feed, and a dielectric ring. The high frequency feed and the dielectric ring have a same axis with the waveguide tube. The waveguide tube has a tubular structure, and is configured to transmit a first electromagnetic wave, the ring groove whose opening direction is the same as an output direction of the first electromagnetic wave is on a wall of the waveguide tube. The high frequency feed is located in the waveguide tube. The dielectric ring is filled between the waveguide tube and the high frequency feed, and has a multi-layer structure. The area sizes of planes that are at layers of the dielectric ring and that are perpendicular to the axis alternately change, and a height of the dielectric ring is less than a height of the waveguide tube.