Antenna device

1. An antenna array, for transmitting or receiving a radio wave in a predetermined wave band, comprising:

a plurality of waveguides extending toward a first direction; and

a plurality of rectangular horns extending toward a direction away from a surface of the plurality of waveguides, wherein

the plurality of waveguides are arranged in a row extending toward a second direction perpendicular or substantially perpendicular to the first direction,

intervals between adjacent ones of the plurality of waveguides are twice as long as a free space wavelength of the radio wave in the predetermined wave band,

a cross section of each of the plurality of waveguides is rectangular with a long side thereof extending toward the second direction and a short side thereof being shorter than the long side thereof;

outer surfaces of the plurality of waveguides, each of which has a width in the second direction, each include a plurality of slots arranged in a row extending toward the first direction, the plurality of slots extending to the outer surfaces;

each of the plurality of slots has a rectangular shape with a short side of thereof extending, toward the first direction and a long side thereof being longer than the short side thereof;

at least two of the plurality of waveguides, which are adjacent to each other, have a same width;

an interval between adjacent ones of the plurality of slots in the first direction is equal or substantially equal to a wavelength of the radio wave in the predetermined wave band in the at least two of the plurality of waveguides;

each of the plurality of slots opens on each of base portions of the plurality of rectangular horns;

each of openings at opposite sides of the base portions of the plurality of rectangular horns include a short side thereof extending toward the first direction and a long side thereof extending toward the second direction, the long side thereof is longer than the short side thereof;

each of the long sides of the openings is longer than each of the long sides of the plurality of slots;

each of the short sides of the openings is longer than each of the short sides of the plurality of slots;

each of the plurality of rectangular horns includes a left face and a right face which oppose each other and which extend toward the first direction, and an upper face and a lower face which oppose each other and extend toward the second direction.

2. The antenna array according to claim 1 , wherein

each of the plurality of rectangular horns further comprises a pair of overhang portions extending toward a center of the plurality of rectangular horns from the base portions of the left face side and the base portions of the right face, respectively.

3. The antenna array according to claim 1 , wherein

at least a portion of a surface of the pair of the overhang portions facing the opening approaches toward each of the plurality of waveguides while being adjacent to the plurality of slots.

4. The antenna array according to claim 2 , wherein

a width of each of the base portions in the second direction is equal to or larger than one and half times the free space wavelength.

5. The antenna array according to claim 1 , wherein

each of the long sides of the plurality of waveguides is smaller than one and half times the free space wavelength and equal to or larger than half of the free space wavelength.

6. The antenna array according to claim 1 , further comprising:

an antenna plate which is a single monolithic member which includes the plurality of rectangular horns at one side thereof and a plurality of grooves at another side thereof, the plurality of slots being located at a bottom of each of the plurality of grooves;

a metal plate arranged at the another side of the antenna plate and closing the plurality of grooves; and

a fixing member configured to fix the metal plate to the antenna plate, located between the plurality of slots.

7. The antenna array according to claim 1 , wherein

at least a portion of the plurality of waveguides are used to transmit the radio wave, while remaining ones of the plurality of waveguides are used to receive the radio wave;

a total number of the plurality of waveguides used to receive the radio wave is larger than a total number of the plurality of waveguides used to transmit the radio wave.

8. The antenna array according to claim 7 , wherein

each of long sides of the openings of the plurality of rectangular horns included in the plurality of waveguides used to transmit the radio wave is longer than each of long sides of the openings the plurality of rectangular horns included in the plurality of waveguides used to receive the radio wave.