Vehicular antenna device

A vehicular antenna device comprising:

• a directional antenna which radiates radio waves in a predetermined direction;
• and
• a radio wave diffusion structure installed vertically above the directional antenna to reflect radio waves radiated upwards from the directional antenna in a lateral direction for omnidirectional spreading,
• wherein the radio wave diffusion structure has a reciprocal cone shape with a base facing upwards and an apex facing the directional antenna, characterized in that:
• the directional antenna is an array antenna formed in a square panel shape and having an upward directionality, the array antenna including a plurality of unit antenna elements arranged upwards, each of the plurality of unit antenna elements is a patch antenna,
• a lateral surface of the radio wave diffusion structure is inwardly curved at a constant radius of curvature R in vertical cross section, and
• a magnitude of the constant radius of curvature R satisfies Equation 1 when a magnitude of wavelength of the radiated radio waves is λ:
• πλ<R<20λ [Equation 1]
• where h is a vertical direction distance between an apex of the radio wave diffusion structure and the directional antenna satisfies Equation 2:
• h
• =
• 3
• ⁢
• d
• +
• λ
• 2
• +
• 2
• ⁢
• π
• ⁢
• R
• 2
• ⁢
• 2
• [
• Equation
• ⁢
• 2
• ]
• wherein d denotes a length of one side of the directional antenna, λ denotes a wavelength magnitude of radio waves radiated from the directional antenna, R denotes the constant radius of curvature of the radio wave diffusion structure, and π denotes a ratio of a circle's circumference to its diameter.