| 摘要 |
A helical antenna having an antenna element covered with an insulating layer is formed by monolithically form the insulating layer so that the antenna element is integrated with the insulating layer. To be more precise, first, a cylindrical shell, which received a core pin in its center hole, is inserted into the antenna element along the longitudinal axis of the antenna element. The antenna element is put in a cavity of a molding die. A molding resin which was heated and molten at a temperature higher than the melting point of the cylindrical shell is injected into the cavity to form an insulating cover over the cylindrical shell and the antenna element. The surface of the cylindrical shell starts softening upon contacting with the molten resin, and sticks around the helically coiled antenna line, whereby the pitch of the antenna element can be maintained substantially constant even if an injection pressure is applied during the molding.
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