Antenna apparatus

Abstract

Good electric characteristics are obtained even after an antenna being further incorporated into an antenna apparatus including an antenna case having a limited space. An antenna device 31 is formed on an antenna substrate 30 installed upright in an antenna base 20. A flat antenna unit 35 is fastened to the antenna base 20 so that the flat antenna unit 35 is immediately below the antenna device 31. If the wavelength of a center frequency in an operating frequency band of the flat antenna unit 35 is », an interval between an upper surface of the flat antenna unit 35 and a lower end of the antenna device 31 is set to about 0.25» or more. Accordingly, it becomes possible to make directional characteristics of radiation in a horizontal plane of the flat antenna unit 35 non-directive without being affected by the antenna device 31 and also to achieve good gain characteristics.

Description

technical field [0001] The present invention relates to a low profile antenna device installed in a vehicle capable of receiving at least FM broadcasts. Background technique [0002] Conventional antenna devices mounted on vehicles are generally configured as antenna devices capable of receiving AM broadcasts and FM broadcasts. In a conventional antenna device, a rod antenna with a length of about 1 m is used for receiving AM broadcast and FM broadcast. The length of this rod antenna is approximately 1 / 4 wavelength in the FM band, but is very short relative to the wavelength in the AM band, so its sensitivity is remarkably reduced. Therefore, conventionally, the rod antenna is made high impedance for the AM band using a high-impedance cable, or is amplified using an AM band amplifier to ensure sensitivity. In addition, there is also used a vehicle-mounted antenna device in which the length of the antenna is shortened to approximately 180 mm to 400 mm by using a helical ant...

AI Technical Summary

Problems solved by technology

[0006] In such a conventional antenna device 101, there is a problem that the appearance and design of the vehicle are damaged due to the rod-shaped portion protruding greatly from the vehicle body, and the rod-shaped portion may be damaged if the rod-shaped portion is forgotten to be put down during storage or car washing. loss of antenna performance

The reason is that the installation height of the planar antenna part 235 on the amplifier substrate 234 becomes high, the distance between the ground and the chip element of the planar antenna part 235 becomes large, and the electrical characteristics of the planar antenna part, especially the radiation Directionality brings influence

Furthermore, in the radiation field of the planar antenna part 235, there is an antenna element 231, which is a large metal body of about 1 / 2 wavelength of the operating frequency of the planar antenna part 235, in the low-elevation angle radiation range. Influenced by reflection, diffraction, etc., the radiation directivity characteristic of the planar antenna part 235 tends to deteriorate significantly

In this way, there is a problem that when an antenna is embedded in an antenna device having an antenna case with only a limited space, it is affected by the existing antenna and cannot obtain good electrical characteristics.

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