Patent ID: 7872609

Claim:
A circular waveguide antenna comprising: a circular waveguide; a feeding portion at one end of a circular waveguide, the feeding portion feeding electromagnetic waves; and a radiation aperture at an opposite end of the circular waveguide, the radiation aperture radiating the electromagnetic waves, wherein the circular waveguide includes a conical horn, with a diameter of a feeding side aperture at the feeding portion end being a , a diameter of the radiation aperture being d, which is larger than the diameter a of the feeding side aperture, and an opening angle being 2α, and if a wavelength of a central frequency of an employed frequency band is λ, then a value α, which is half of the opening angle 2α, the diameter d of the radiation aperture and the value of the wavelength λ of the central frequency of the employed frequency band are at least one of set in predetermined ranges and set such that α, d and λ satisfy a predetermined relationship with one another.