Antenna device

An antenna device comprising:

• a first dielectric substrate having a first surface and a second surface;
• a first antenna element and a second antenna element on the first surface of the first dielectric substrate;
• a ground conductor on the second surface of the first dielectric substrate;
• and
• an isolation structure between the first and second antenna elements, wherein
• the isolation structure includes:
• a first conductor between the first and second antenna elements on the first surface of the first dielectric substrate;
• and
• a plurality of first via conductors that penetrate the first dielectric substrate and electrically connect the first conductor to the ground conductor,
• the first dielectric substrate has a dielectric constant of εr,
• the first antenna element is a transmitting antenna for transmitting a signal with a wavelength λ1 (mm),
• in a plan view, the plurality of first via conductors are arranged at a predetermined pitch in a second direction perpendicular to a first direction in which the first and second antenna elements are arranged, and each of the first via conductors has a height h1 (mm),
• the first conductor protrudes with a length d1 (mm) from centers of the first via conductors toward the first antenna element in the first direction, and
• a value of (d1×2+h1)/(λ1/√εr) falls within a range from 0.40 to 0.60.