Antenna apparatus

Abstract

Excellent electrical characteristics are obtained even when an antenna is further assembled to an antenna device provided with an antenna case having only a limited space. An antenna element (31) is formed on an antenna substrate (30) which is arranged upright on an antenna base (20). A planar antenna unit (35) is firmly attached to the antenna base (20) so that a planar antenna unit is positioned directly below the antenna element (31). When the wavelength of the center frequency in the operation frequency band of the planar antenna unit (35) is expressed by lamda, an interval between an upper surface of the planar antenna unit (35) and a lower end of the antenna element (31) is approximately 0.25 lamda or more. Thus, radiation directivity of the planar antenna unit (35) within a horizontal surface is permitted to be nondirectional without being affected by the antenna element (31), and excellent gain characteristics can be obtained.

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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