Patent Application
20100231451
The present invention relates to an antenna device whose directivity is switched.
The following two factors are primarily responsible for unstable wireless communication. The first factor is a failure to acquire sufficient receiving electric field intensity because of a distance between wireless devices that is too long in relation to an output of an electric wave. In the case of this problem, an antenna of at least one of the two wireless devices is provided with directivity, and main probes of the devices are oriented to each other. Consequently, the wireless devices can receive a radio wave at sufficient, stable electric field intensity.
The second factor is fading that arises from interference caused by waves reflected from walls, a ceiling, and the like. This problem noticeably arises at a location where no substantial intensity difference exists between a direct wave and a reflected wave of a radio wave. Even in the case of this problem, an antenna of a receiver is provided with directivity, and the main probe of the receiver is directed toward a desired wave, and directivity is set so as to exhibit a null point in the other directions. As a consequence, the receiver does not receive radio waves other than the desired wave, so that interference can be prevented.
The solution is appropriate, so long as a wireless communication scheme is an SISO (Single Input Single Output) method, and there is adopted a diversity in which a receiver simply selects one from a plurality of antennas. However, when two respective antennas of a receiver have directivity; when one antenna receives a direct wave; and when the other antenna receives an indirect wave, the following problems arise. Namely, when the indirect wave is longer than the direct wave in terms of a delay time as compared with an assumed guard interval time, the indirect wave acts as the source of interference; hence, demodulation cannot be performed by means of a simple configuration in which the receiver uses only an OFDM modulation scheme.
Patent Document 1: JP-T-2006-506899
Patent Document 2: U.S. Published Patent Application No. 2004-0098745
Patent Document 3: WO2004/047373
According to a MIMO (Multi Input Multi Output) scheme adopted for IEEE802.11n that is one of the wireless LAN standards, a receiver receives a radio wave with a plurality of antennas and produces one propagation path by active utilization of a path difference between the radio waves. A wireless device used in a wireless communication system adopting the MIMO scheme has an antenna device having a plurality of nondirective antennas, such as dipole antennas and sleeve antennas. However, correlation between antennas becomes greater without conceiving a contrivance, such as assurance of a sufficient interval between antennas and a combination of different polarized waves by tilting the respective antennas in different directions, which in turn deteriorates transmission quality. For these reasons, the antenna device of the wireless device compliant with the MIMO scheme cannot be made compact.
An IFE (In-Flight Entertainment) system that distributes movies, music, games, and the like, to passenger terminals in a passenger cabin of an aircraft, and the like, has been known. The IFE system primarily has a server and client terminals (SEB: seat entertainment BOX). A form for wirelessly transmitting information from a server to client terminals by way of WAP (Wireless Access Points) as well as a form for establishing communication by connecting a server to client terminals by way of wires are conceivable as a communication scheme for the IFE system. Since the passenger cabin of the aircraft is a space enclosed by metal, such as aluminum, there are many high-level waves reflected from a ceiling, walls, and a floor. Since the MIMO scheme actively utilizes reflected waves as mentioned above, the scheme is considered to be a scheme effective in such a radio wave environment. Moreover, the client terminals can efficiently receive reflected waves, so long as a plurality of antennas provided in the respective client terminals are provided with different directivities.
However, the client terminals are principally disposed in the neighborhoods of passenger seats and hence cannot be made bulky. For this reason, when the communication scheme of the IFE system is wireless, the antenna device provided in the client terminal must be compact. Further, a radio wave environment for a position where the client terminal is to be disposed is various. For these reasons, it is desirable that the directivity of the antenna device be switched by electrical operation.
An object of the present invention is to provide a compact antenna device capable of switching directivity by means of electrical operation.
The present invention provides an antenna device comprising a linear antenna element; a passive element section provided in proximity to the antenna element; and a control section that controls the passive element section, wherein the passive element section includes a linear line arranged in parallel to the antenna element; and an impedance adjustment section that adjusts impedance of the passive element section.
In the antenna device, the impedance adjustment section is a diode electrically connected to the linear line.
In the antenna device, the passive element section is a dipole element in which two quarter-wave lines are arranged in a straight line; and the impedance adjustment section is a diode disposed at a center of the dipole element.
In the antenna device, the antenna element and the passive element section are provided in parallel to each other; and an electrical length from an end of the antenna element to the passive element section is a quarter wavelength.
In the antenna device, the passive element sections are respectively provided at both ends of the antenna element.
In the antenna device, the control section outputs a control signal for controlling the impedance adjustment section.
The antenna device further includes two inductor sections, one being provided in a wire connecting the passive element section to the control section, and the other being provided in a wire connecting the passive element section to a ground.
In the antenna device, the antenna element is a sleeve antenna or a dipole antenna.
An antenna device of the present invention enables switching of its directivity by means of electrical operation. Moreover, since an electrical length from an antenna element to a passive element is merely a quarter wavelength, the antenna device can be made compact when the antenna device is used at a high frequency.
An embodiment of the present invention will be described hereunder by reference to the drawings.
As mentioned above, the passive elements 45a and 45b are brought into the ON position or the OFF position, thereby enabling realization of four different directivities. As mentioned above, the states of the passive elements 45a and 45b are controlled by an analogue control signal output from the control section 33.
The converter section 83 compares the voltage applied from the constant voltage generation section 82 with the voltage applied from the voltage conversion section 87, and outputs a signal 88 conforming to a comparison result. The signal control section 84 outputs an analogue control signal 86 complying with the respective signals output from the four converter sections 83. The signal control section 84 stores a table showing a relationship between the respective signals output from the four converter sections 83 and the analogue control signal 86. The power source section 81 supplies power to the four constant voltage generation sections 82, the voltage conversion section 87, the four converter sections 83, and the signal control section 84.
The voltage of the analogue control signal 86 is any of voltages ranging from 3 to 5V at increments of 0.5V. When a plurality of types of voltages are required, the essential requirement is to make a step interval smaller than a value of 0.5V. Further, the signal output from the signal control section 84 is not limited to an analogue format and may also be a digital format, such as a serial output or a parallel output.
In the present embodiment, choke coils 61 are provided in the respective two wires 57a and 57b that connect the antenna device 31 to the control section 33, as shown in
In the present embodiment,
As mentioned above, the client terminal 14 of the IFE system has the three antenna devices 31 of the present embodiment capable of switching their directivities by electrical operation; hence, the client terminal 14 can perform superior communication of stable quality during wireless communication utilizing the MIMO scheme in a radio wave environment where there are many reflected waves.
In the embodiment, the antenna device 31 has the sleeve antenna 43 and the passive elements 45a and 45b, but a dipole antenna may also be used in place of the sleeve antenna 43.
Although the present invention has been described in detail by reference to a specific embodiment, it is manifest to those skilled in the art that the present invention be susceptible to various alterations or modifications within the spirit and scope of the present invention.
The present patent application is based on Japanese Patent Application (JP-2006-287791) filed on Oct. 23, 2006, the contents of which are incorporated herein for reference.
An antenna device of the present invention is useful as a compact antenna device, or the like, capable of switching its directivity by means of electrical operation.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-287791 | Oct 2006 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2007/070634 | 10/23/2007 | WO | 00 | 4/22/2009 |
