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Annular microstrip antenna element and radial line antenna system employing the same
| Details |
Inventors: Nishikawa, Kunitoshi; Watanabe, Toshiaki; Ogawa, Masaru; Harada, Tomohisa;
Assignee: Kabushiki Kaisha Toyota Chuo Kenkyusho (Aichi-ken, JP)
Primary Examiner: Le; Hoanganh T.
Assistant Examiner: Phan; Tho
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier & Neustadt, P.C.
In an annular microstrip antenna element, an annular radiant conductor plate is mounted on a ground conductor plate via a dielectric layer. A coaxial transmission line is provided, whose external conductor is connected to the ground conductor plate, and whose central conductor is connected to the radiant conductor plate, via a feeding point, with a pair of microstrip lines. The pair of microstrip lines extend from the feeding point to two connecting points on the radiant conductor plate, forming an angle between them like a V shape. By varying the angle, it is possible to adjust the input impedance of the annular microstrip antenna element at the feeding point, so that impedance matching with the coaxial transmission line is achieved. In a radial line antenna system comprising a plurality of the antenna elements, the antenna elements are mounted on concentric circles with a constant space between the adjacent antenna elements, thereby reducing undesirable electromagnetic coupling. |
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DETAILED DESCRIPTION The present invention has been conceived to overcome the above problems, and therefore aims to provide an annular microstrip antenna element with a simple structure, which enables impedance matching.
The present invention further aims to provide a radial line antenna system with superior characteristics employing the annular microstrip antenna element of the present invention.
An antenna element of the present invention comprises: a dielectric layer; a ground conductor plate mounted on one surface of the dielectric layer; an annular radiant conductor plate formed on the other surface of the dielectric layer so as to surround a symmetrical area with respect to a predetermined reference line on the surface of the dielectric layer; a feeding point located on the reference line; and a pair of microstrip lines mounted within the area in a symmetrical manner with respect to the reference line, for connecting the feeding point to two points on the annular radiant conductor plate.
According to the present invention, the feeding point is connected via a pair of microstrip lines to the annular radiant conductor plate at two connecting points.
With such an arrangement, the input impedance of the annual microstrip antenna element 10 at the feeding point varies depending on the extent of an angle formed by the pair of microstrip lines.
In other words, by varying the extent of the angle, it is possible to easily adjust the input impedance of the antenna element 10 so as to match with that of the transmission line, such as a coaxial transmission line feeding a radio frequency power to the antenna element 10.
In general, in the case of an antenna element employing an annular radiant conductor plate, the input impedance of the antenna element is higher than that of the coaxial transmission line even when a radio frequency power is fed via the inner edge of the annular radiant conductor plate.
In the present invention, however, by simply setting the angle formed by the pair of microstrip lines to a predetermined extent, it is possible to achieve impedance matching between the antenna element and the transmission line without the need to separately provide a circuit for matching impedance
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