Patent Application
20130257661
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2012-079795, filed Mar. 30, 2012, the entire contents of which are incorporated herein by reference.
Embodiments described herein relate generally to an antenna apparatus and an electronic device including the antenna apparatus.
There have been proposals to make portable electronic devices such as personal computers and tablet type terminals incorporate radio devices for receiving analog television broadcasts, data broadcasts, mobile data broadcasts, and the like so as to allow to receive broadcast signals or data from the radio devices and display them on displays or to store them in memories.
As an antenna used in a radio device for broadcast reception, an antenna apparatus is generally used, which allows selection between a state in which an antenna element is retracted into the housing and a state in which the antenna element extends from the housing. An antenna apparatus of this type allows the user to view and listen to broadcasts while selectively using the use patterns of the antenna in accordance with surrounding conditions.
The above conventional antenna apparatus, however, has the following problem to be solved. That is, using the antenna element while keeping it outside the housing can easily obtain good characteristics. When using the antenna element while accommodating it in the housing, since the antenna element receives the influences of the ground portion on a printed wiring board set in the housing and the like, the resonance frequency shifts to a value lower than a desired value. This may lead to a deterioration in reception performance.
A general architecture that implements the various features of the embodiments will now be described with reference to the drawings. The drawings and the associated descriptions are provided to illustrate the embodiments and not to limit the scope of the invention.
Various embodiments will be described hereinafter with reference to the accompanying drawings.
In general, according to one embodiment, an antenna apparatus of the embodiment is provided in an electronic device including a ground portion and a feed point in a housing, and includes an antenna element and a parasitic element. The antenna element includes an element main body whose first end portion is connected to the feed point and second end portion as the other end portion is open, with the element main body being configured to be selectable between a first state in which the element main body is retracted into the housing of the electronic device and a second state in which the element main body extends from the housing. The parasitic element is disposed such that when the antenna element is in the first state, the first end portion is connected to the element main body of the antenna element and the second end portion is connected to the ground portion.
According to this embodiment, in the second state in which the antenna element is extends from the housing, it is possible to receive broadcast waves at high gain without any influence of the housing and the like. In contrast to this, in the second state in which the antenna element is retracted into the housing, a portion of the antenna element which is located near its distal end portion is physically or electrically connected to the distal end portion (open end) of the parasitic element. As a consequence, the antenna element is forcibly grounded to the ground portion via the parasitic element, and operates as a folded antenna element having a length ½ the wavelength of a broadcast wave as a reception target in cooperation with the parasitic element. Even if, therefore, the antenna element is located near the ground portion, it is possible to reduce the influence of the ground portion on the antenna element. This makes it possible to prevent a frequency shift with respect to the resonance frequency of a broadcast wave as the reception target. In addition, the antenna element and the parasitic element operate as a folded antenna element having an element length ½ the wavelength. This can increase the reception gain (Peak Gain) of a broadcast wave as compared with when using an antenna element as an antenna element having an element length ¼ the wavelength.
That is, the embodiment can provide an antenna apparatus which can obtain good reception characteristics by suppressing a resonance frequency shift when using the antenna element while accommodating it in the housing, and an electronic device including the antenna apparatus.
The electronic device is formed from a notebook personal computer or portable television terminal including a radio circuit, and has a ground portion (also called a ground plate or GND plate) 2 accommodated in the housing 1. The ground portion 2 is the one using part of a metal housing or a metal member such as a copper foil, or is formed from a printed circuit board or multilayer board on which a metal ground pattern is formed.
Note that the electronic device may be a portable information terminal such as a navigation terminal, cellular phone, smart phone, PDA (Personal Digital Assistant), or tablet-type computer in addition to a notebook personal computer or portable television terminal.
An antenna apparatus is provided in this electronic device. The antenna apparatus includes an antenna element 3 and a parasitic element 5. The antenna element 3 is formed from an L-shaped linear monopole element having the proximal end portion connected to a feed point 4, and the distal end portion open. The antenna element 3 is movably mounted on the housing 1 through a connecting mechanism (not shown). This allows the antenna element 3 in the state in which it is retracted into the housing 1, i.e., the state shown in
On the other hand, the parasitic element 5 is obtained by folding a linear element into a crank shape, with the proximal end portion being connected to the ground portion 2. The distal end portion of the parasitic element 5 is positioned so as to be electrically connected to the antenna element 3 when the antenna element 3 is retracted into the housing 1.
This arrangement makes it possible to receive broadcast waves at high gain without any influence of the housing 1 and the like while the antenna element 3 extends from the housing 1 as shown in
In contrast, in the state in which the antenna element 3 is retracted into the housing 1 as shown in
In addition, the antenna element 3 and the parasitic element 5 operate as a folded antenna element having an element length ½ the wavelength. This can increase the reception gain (Peak Gain) of a broadcast wave as compared with when using the antenna element 3 as an antenna element having an element length ¼ the wavelength.
A first matching circuit 6 is connected between the proximal end portion of an antenna element 3 and a feed point 4. Likewise, a second matching circuit 7 between the proximal end portion of a parasitic element 5 and a ground portion 2. The matching circuits 6 and 7 are used to match the resonance frequency of the folded antenna element constituted by the antenna element 3 and the parasitic element 5 with the frequency of a broadcast wave as a reception target.
This arrangement can accurately match the resonance frequency of the folded antenna element constituted by the antenna element 3 and the parasitic element 5 with the frequency of a broadcast wave as a reception target. In addition, connecting the first matching circuits 6 and 7 can shorten the element lengths of the antenna element 3 and parasitic element 5, thereby reducing the mounting volume of the antenna apparatus.
Examples 1 and 2 of the antenna apparatus according to the second embodiment will be described below.
As shown in
As shown in
The antenna apparatuses using no parasitic element 5, shown as Reference Examples 1 and 2 in
As is obvious from the above comparison, the antenna apparatus according to the second embodiment can obtain a very high effect of improving a frequency shift by adding the parasitic element 5 to the antenna element 3 so as to make it operate as a folded antenna element.
A second matching circuit 7 provided between a parasitic element 5 and a ground portion 2 is constituted by two matching circuits 71 and 72 having different inductance values and a switching circuit 8. The switching circuit 8 is formed from, for example, a switch which is manually operated for switching or a semiconductor switch which performs switching operation in accordance with a switching control signal output from a control circuit (not shown). The switching circuit 8 connects one of the two matching circuits 71 and 72 between the parasitic element 5 and the ground portion 2 by switching operation.
In this arrangement, setting inductance values for the matching circuits 71 and 72 in accordance with the frequency of a system as a reception target can receive the frequency of the system as the reception target by only switching the switching circuit 8. The matching circuits 71 and 72 are switched between the parasitic element 5 and the ground portion 2. This makes it possible to maintain the high-gain antenna characteristics without any influence of the loss caused by the switching circuit 8 while the antenna element 3 extends from the housing 1.
A portion of an antenna element 3 which is parallel to a ground portion 2 is formed into a helical shape. This can decrease the element length of the antenna element 3 as compared with the case in which a linear element like that in the second embodiment is used. This makes it possible to reduce the mounting volume for antenna operation.
Assume that as shown in
The above embodiments have exemplified the case in which broadcast waves such as analog television broadcast, data broadcast, and mobile data broadcast waves are received. However, the embodiments can also be applied to a case in which other radio systems such as a terrestrial digital radio broadcast system, a disaster prevention broadcast system, a cellular phone network, and a wireless local area network (wireless LAN) transmit and receive radio signals.
In addition, the above embodiments can be executed by variously modifying the types and functions of electronic devices and the shapes, sizes, and the like of the antenna elements, parasitic elements, and the ground portions of the antenna apparatuses.
While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-079795 | Mar 2012 | JP | national |
