US-12620696-B2 - Antenna device for vehicle

Abstract

An antenna device that is attached to a vehicle, the antenna device including: a resin base; a metal base arranged on the resin base; a metal plate located above the resin base and attached to the metal base so as to be superimposed on a portion of the metal base; a substrate arranged on the metal base; an antenna connected to the substrate; and a plurality of fasteners which fix the metal base and the substrate, wherein one of the plurality of fasteners is positioned at a top-view superimposed area of the metal base and the metal plate.

Inventors

• Noritaka TERASHITA
• Yusuke Yokota
• Takashi Kaneko

Assignees

• YOKOWO CO., LTD.

Dates

Publication Date

20260505

Application Date

20240215

Priority Date

20171220

Claims (8)

1. 1 . An antenna device that is attached to a vehicle, the antenna device comprising: a plate-shaped body made by resin; a metal plate arranged on the plate-shaped body; a substrate fixed to the metal plate; and an antenna connected to the substrate, wherein the metal plate is formed from at least one of sheet metal and conductive resin, the metal plate includes a portion which is different in a height between a lower surface of the plate-shaped body and a lower surface of the metal plate, the metal plate is placed to be opposed to a roof of the vehicle, a projection portion for fixing to the roof is provided on a surface of the metal plate facing the roof, the metal plate and the roof are electrically connected together via the projection portion, and a resonance frequency that occurs due to the roof and the metal plate that are electrically connected together via the projection portion is out of a communication frequency band of the antenna.
2. 2 . The antenna device according to claim 1 , wherein the metal plate includes a cutout portion, and at least a part of the antenna overlaps the cutout portion in a top view.
3. 3 . The antenna device according to claim 1 , wherein the plate-shaped body has a pedestal portion inhibiting a position shift of the metal plate.
4. 4 . The antenna device according to claim 1 , wherein the surface of the metal plate facing the roof has a step.
5. 5 . The antenna device according to claim 1 , wherein a protrusion for supporting the substrate is provided on a surface of the metal plate opposite to the surface facing the roof.
6. 6 . The antenna device according to claim 1 , wherein the metal plate has a hole.
7. 7 . The antenna device according to claim 1 , wherein the metal plate enhances strength of the plate-shaped body made by resin.
8. 8 . The antenna device according to claim 1 , wherein a size of the metal plate in a longitudinal direction of the antenna device is longer than a size of the metal plate in a width direction of the antenna device.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS The present application is a continuation of U.S. application Ser. No. 17/894,180, filed Aug. 24, 2022, which is a continuation of U.S. application Ser. No. 16/955,800, filed Jun. 19, 2020 (now U.S. Pat. No. 11,462,822), which is based on PCT filing PCT/JP2018/047080, filed Dec. 20, 2018, which claims priority to JP 2017-244548, filed Dec. 20, 2017, the entire contents of each are incorporated herein by reference. TECHNICAL FIELD The present invention relates to an antenna device for vehicle that is attached to a roof of a vehicle. BACKGROUND ART An antenna device for vehicle that is attached to a roof of a vehicle such as an automobile has been known, the antenna device for vehicle accommodating an antenna element in a streamlined case in consideration of fluid resistance. In general, the antenna device for vehicle is mounted on a center in a rear portion of the roof and may be referred to as “shark fin antenna”, “dolphin antenna”, or the like because of the figure of the vehicle with the antenna device for vehicle mounted and the appearance of the antenna device for vehicle. For example, Patent Literature 1 specifically discloses an antenna device for vehicle in which an antenna case is put on a resin base and a space for accommodating a metal base functioning as a ground plate, an antenna element, and so forth is thereby defined. Patent Literature 1 describes a structure which is provided with a conductor plate having a plate spring portion between the metal base and a roof and thereby prevents a decrease in antenna gain due to unnecessary resonance. That is, in a configuration of Patent Literature 1, a capacitance is increased by the conductor plate provided between the metal base and the roof, its resonance frequency is shifted to a lower side than a communication frequency band of the antenna element, and a decrease in antenna gain may thereby be prevented. CITATION LIST Patent Literature Patent Literature 1: Japanese Patent Laid-open No. 2016-32166 SUMMARY OF INVENTION Technical Problem In patent Literature 1, waterproofing is conducted for a gap between a resin base and a roof by a pad, a sealing member, or the like, and reaching of rainwater and so forth to a portion around a conductor plate is prevented as much as possible. However, the shape of the roof as a portion to which an antenna device for vehicle is mounted is not flat. Specifically, the roof has a mildly curved surface, the manner of the curve is different depending on the kind of vehicle or the like on which the antenna device for vehicle is mounted. Thus, it is anticipated that a case will occur where perfect waterproofness may not be secured even by the pad or the sealing member. In this case, corrosion may occur to the conductor plate. A drastic measure against such corrosion of the conductor plate is omission of the conductor plate. Then, a function for adjusting a resonance frequency of unnecessary resonance so as to be out of communication frequencies, which is given by the conductor plate, has to be ensured by another method. For example, it is possible to prepare plural kinds of metal bases with different resonance frequencies of the unnecessary resonance and to exchange the metal bases in accordance with the mounting condition. However, the metal base is a precision die-cast product of aluminum or the like. Thus, changes in design, of course, and maintaining multiple kinds take manufacturing cost and management cost compared to a case of maintaining few kinds. Further, it may be considered that one kind of metal base works adequately if a long side dimension of the metal base is made longer and the resonance frequency of the unnecessary resonance is thereby sufficiently separated from a lower limit of a communication frequency band with a relatively high safety factor. However, this may not be considered as a really preferable solution in terms of costs for the antenna device for vehicle, size reduction of the antenna device for vehicle, appearance of the antenna device for vehicle when mounted on the vehicle, and so forth. In addition, because the shape of the roof is actually not flat as described above and the manner of the curve is not uniform, the capacitance occurring between the metal base and the roof (ground capacitance) is not determined. Thus, even if the metal base is designed very well, a case may occur where designed performance may not sufficiently be provided depending on the kind of vehicle or the like on which the metal base is mounted. A challenge for the present invention is to provide a technique for realizing an antenna device for vehicle that prevents a decrease in antenna gain due to unnecessary resonance by a method other than providing a conductor plate between a metal plate and a roof. Solution to Problem A first aspect of the present invention provides an antenna device for vehicle that is attached to a roof of a vehicle, the antenna device for vehicle includin