Antenna device

1. An antenna device comprising:

a feeder to feed an electromagnetic wave;

a ground conductor;

a substrate having a first plane on which the feeder is formed and a second plane on which the ground conductor is formed, the second plane being opposite to the first plane;

a feed line having one end coupled with the feeder, the feed line being a strip conductor formed on the first plane; and

N (N is an integer greater than 2) radiation elements formed by a strip conductor in the feed line, each of the N radiation elements comprising one or more coupling portions to the feed line,

wherein each of a first to an (N−1)th radiation elements out of the N radiation elements, when counted from the feeder side, is formed with a recessed portion for adjusting power of the electromagnetic wave that passes through the respective radiation element as a power adjustment portion atone of the one or more coupling portions to the feed line that is on an opposite side of the feeder,

wherein one or more radiation elements out of the N radiation elements are formed with a hole, and

wherein each of the N radiation elements is formed with another recessed portion on a side facing the feeder for adjusting an input impedance of the respective radiation element as an impedance matching portion at a respective coupling portion on the feeder side out of the one or more coupling portions to the feed line.

2. The antenna device according to claim 1 , wherein a line length of the feed line between an i-th (i is an integer in a range between 1 and (N−1)) radiation element and an (i+1)th radiation element among the N radiation elements, when counted from the feeder side, is given by a length with which a sum of a first passing phase that is a phase of an electromagnetic wave passing through the i-th radiation element and a second passing phase that is a phase of an electromagnetic wave passing through the feed line between the i-th radiation element and the (i+1)th radiation element satisfies a conditional expression below:

φ 1 ( i )+φ 2 ( i )=− k×d ( i )×sin θ+2 mπ,   [Conditional Expression]

where φ 1 (i) denotes the first passing phase,

φ 2 (i) denotes the second passing phase,

k denotes the wave number at a used frequency of the electromagnetic wave,

d(i) denotes the line length of a feed line between an i-th radiation element and an (i+1)th radiation element,

θ denotes an orientation of the electromagnetic wave which is represented by an angle formed with respect to a front direction of the antenna device, and

m is an integer.

3. The antenna device according to claim 1 , wherein the radiation elements have a polygonal shape.

4. The antenna device according to claim 1 , wherein the radiation elements have an elliptical shape.

5. The antenna device according to claim 1 , wherein a plurality of sets of the feeder, the feed line, and the N radiation elements is formed on the substrate.