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Antenna for radio apparatus
| Details |
Inventors: Takei, Ken; Ohnishi, Masami;
Assignee: Hitachi, Ltd. (Tokyo, JP)
Primary Examiner: Hajec; Donald
Assistant Examiner: Le; Hoanganh
Attorney, Agent or Firm: Antonelli, Terry, Stout & Kraus
An antenna for radio apparatus comprises a first conductor taking a helical form, a second conductor which extends to and fro in sequence substantially in a direction of the center axis of the helical form of the first conductor to take, as a whole, a meandering form which is spaced apart from the first conductor and surrounds the center axis, and a dielectric member which lies at least between the first and second conductors. A portion of the first conductor is electrically connected to a portion of the second conductor, and either a portion of the first conductor or a portion of the second conductor acts as a feeding point. |
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DETAILED DESCRIPTION An object of the invention is to provide a compact antenna which can obtain a desired matching characteristic without using the separate matching circuit which limits miniaturization of the antenna system as a whole and forms a factor of raising cost when the antenna is incorporated into the terminal.
To accomplish the above object, according to one aspect of the present invention, an antenna comprises a first conductor taking a helical form, a second conductor which extends to and fro in sequence substantially in a direction of the center axis of the helical form of the first conductor to take, as a whole, a meandering form which is spaced apart from the first conductor and surrounds the center axis, and a dielectric member which lies at least between the first and second conductors, a portion of the first conductor being electrically connected to a portion of the second conductor and either a portion of the first conductor or a portion of the second conductor acting as a feeding point.
Firstly, the operation of the invention will be described which proceeds when an intermediate portion (a portion between one end and the other end) of the second conductor is used as a feeding point.
In this case, the second conductor forms, as viewed from the feeding point, two transmission lines in which the radiation resistance results in loss.
One of the two transmission lines is a first transmission line formed of a portion (first portion) of the second conductor lying between the feeding point and one end and having an electrical connecting point to the first conductor.
The other of the two transmission lines is a second transmission line formed of a portion (second portion) of the second conductor lying between the feeding point and the other end and having no electrical connecting point to the first conductor.
If the length of the first portion of the second conductor is set to be sufficiently long for a desired exciting frequency acting on the antenna, then the input impedance of the first transmission line, as viewed from the feeding point, has a positive imarginary conponent of impedance (inductance)
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TV Signal 
