This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2008-198038, filed on Jul. 31, 2008, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to an antenna device, and relates to, for example, a tunable antenna having a variable capacity element.
2. Related Art
JP-A 2005-150937 (Kokai) and JP-A 2005-210568 (Kokai) disclose a tunable antenna in which a low profile antenna such as an inverted-F antenna and a ground plane are connected each other through a variable capacity element to change the operating frequency of the antenna by changing the capacity value of the variable capacity element.
However, the above tunable antenna requires a large range of capacity variable ratio from a small capacity value to a large capacity value to change the operating frequency, which leads to a problem that the loss of the variable capacity element becomes large in the operation at a low frequency since high-frequency current easily flows due to a large capacity value.
Further, when a plate-like element is used, the operation over a broad band can be achieved with high efficiency. However, in the end, the required capacity variable width becomes large and the loss of the element becomes large in the operation at a low frequency.
According to an aspect of the present invention, there is provided with an antenna device comprising: a ground plane, a first radiating element, a second radiating element, a variable capacity element and a capacity controller. The first radiating element has a first conductive element and a second conductive element. A one end of the second conductive element is connected to a one end of the first conductive element and the other end of the second conductive element is connected to the ground plane. The second radiating element has a third conductive element and a fourth conductive element. A one end of the third conductive element faces the other end of the first conductive element, and a one end of the fourth conductive element is connected to the other end of the third conductive element and the other end of the fourth conductive is connected to the ground plane. A one end of the variable capacity element is connected to the other end of the first conductive element and the other end of the variable capacity element is connected the one end of the third conductive element. A capacity controller controls the capacity of the variable capacity element.
Embodiments according to the present invention will now be explained with reference to the accompanying drawings.
The antenna device includes: a ground plane 101 of a radio communication terminal; an inverted L-shaped antenna element (first radiating element) 103 having a one end serving as an open end and the other end connected to a radio unit 102 through a feeding point P; an inverted L-shaped passive element (second radiating element) 104 having a one end facing the one end of the inverted L-shaped antenna element 103 and the other end connected to the ground plane 101; a variable capacity element 105 arranged between the inverted L-shaped antenna element 103 and inverted L-shaped passive element 104; and a capacity controller 108 to control the capacity of the variable capacity element 105.
The inverted L-shaped antenna element 103 includes a first conductive element 103a and a second conductive element 103b, the second conductive element 103b having a one end connected to a one end of the first conductive element 103a and the other end connected to the feeding point P arranged on the ground plane. The first conductive element 103a is arranged approximately in parallel to the surface of the ground plane 101, while the second conductive element 103b is arranged approximately perpendicular to the surface of the ground plane 101. Here, the connection between the first conductive element 103a and the second conductive element 103b means that the first conductive element and the second conductive element are electrically connected, and it does not matter whether or not the first conductive element and the second conductive element are separated from each other. That is, the first conductive element and the second conductive element can be connected to each other by physically connecting these elements through soldering etc. or by forming these elements into one conductive element. As stated above, the first and second conductive elements can be separated from or integrated with each other. By integrating the first and second conductive elements with each other, the number of processes to manufacture the radiating element can be decreased compared to the case where the first conductive element and the second conductive element are physically connected.
The inverted L-shaped passive element 104 includes a third conductive element 104a having a one end facing the other end of the first conductive element 103a and a fourth conductive element 104b having a one end connected to the other end of the third conductive element 104a and the other end connected to the ground plane 101. The third conductive element 104a is arranged approximately in parallel to the surface of the ground plane 101, while the fourth conductive element 104b is arranged approximately perpendicular to the surface of the ground plane 101. As in the first conductive element 103a and the second conductive element 103b, the third conductive element and the fourth conductive element can be separated from or integrated with each other.
The capacity controller 108 includes a voltage supplier 106 to supply hold voltage as a control signal to the variable capacity element 105 through a control line 100, and an applied voltage controller 107 to control the hold voltage of the voltage supplier 106.
The variable capacity element 105 has a terminal connected to the end of the inverted L-shaped antenna element 103, a terminal connected to the end of the passive element 104, and a terminal to receive the control signal from the voltage supplier 106 through the control line 100 to form the capacity depending on the received control signal. A MEMS capacitor, for example, can be used as the variable capacity element 105. By using a MEMS element, the effect of low strain and low loss can be achieved.
With the above structure, the capacity variable width required to operate the antenna in a desired frequency band becomes smaller compared to the conventional antenna in which the variable capacity element is connected between the end of the inverted-F antenna and the ground plane. Accordingly, the capacity value can be restrained to be smaller than that of the conventional antenna in the operation at a low frequency, by which high-frequency current hardly flows through the variable capacity element and the loss of the variable capacity element can be decreased. Hereinafter, this antenna device will be explained in more detail.
When the ends of the antenna element and the passive element are connected through the capacity element as in the antenna device of
Each of a symbol 210 in
The present embodiment is focused on the mode 1 of
Hereinafter, referring to
In
As in
As shown in
As seen from
The variable capacity element 118 has a first terminal connected to the end of the antenna element 103 and a second terminal connected to the end of the passive element 104, and forms capacity depending on the voltage applied between the two terminals. A diode, for example, can be used as the variable capacity element 118. Concretely, voltage is applied between the both terminals of the variable capacity element 118 by applying voltage between a signal line 115 of the antenna element and the ground plane 101. Accordingly, peripheral parts of the antenna element can be easily manufactured.
A direct current component cutter 109 is arranged on the signal line 115 between the feeding point P and the radio unit 102 to cut the direct current component of a high frequency signal generated by the radio unit 102.
A direct current component supplier 116 is arranged to supply a signal of the direct current component to the signal line 115. The direct current component supplier 116 has a voltage supplier 112 to hold voltage and output the hold voltage, a variable capacity controller 117 to set the voltage of the voltage supplier 112, and a high frequency component cutter 110 to extract the direct current component by cutting the high frequency component from the signal output from the voltage supplier 112 to output the direct current component to the signal line 115.
The high frequency signal output from the direct current component cutter 109 is combined with the direct current component output from the high frequency component cutter 110 to be supplied to the feeding point P. Accordingly, the first terminal of the variable capacity element 118 is connected to the potential of the direct current component, while the second terminal of the variable capacity element 118 is connected to the ground potential (the ground plane 101) through the passive element 104, by which the voltage depending on the difference between the both potentials is applied between the first and second terminals.
In the suggested antenna as shown in
The control line 100 to supply the control signal to the variable capacity element 105 is arranged in the position where the distance between the control line 100 and the antenna element 103 and the distance between the control line 100 and the passive element 104 are approximately the same. Accordingly, the influence exerted on the control line 100 by the antenna element 103 and the influence exerted on the control line 100 by the passive element 104 are counteracted with each other, by which the influence exerted on the control line 100 can be decreased. As in
The antenna device of
The antenna element 103(2) corresponds to a third radiating element, for example, while the passive element 104(2) corresponds to a fourth radiating element, for example. The variable capacity element 105(2) corresponds to a second variable capacity element, for example. The applied voltage controller 107(2) and the voltage supplier 106(2) form a second capacity controller, for example.
An element portion which is connected to the feeding point P and is perpendicular to the ground plane 101 is shared between the antenna element 103(2) and the antenna element 103(1). In the example shown in
The antenna device of
The antenna device on the left side includes two of the passive elements 104(3) and 104(2), which are shorter than the antenna elements 103(1) and the passive element 104(1) of the antenna device on the right side, respectively. Similarly to the antenna device on the right side, the antenna device on the left side has two of the resonance modes 1 and 2, and operates in the resonance mode 1. With the structure as stated above, the degrees of freedom in design can be increased, and the operation at a plurality of resonance frequencies in a broad band can be easily achieved, for example. Note that the effect of the present invention can also be achieved when the antenna device on the left side is arranged apart from a conventional antenna device instead of the antenna device of
The suggested antenna explained hereinbefore can operate as an antenna to receive terrestrial digital broadcasting by being mounted in a mobile terminal, a notebook PC, an FPD (Flat Panel Display), and a small AV terminal.
The present invention is not limited to the exact embodiments described above and can be embodied with its components modified in an implementation phase without departing from the scope of the invention. Also, arbitrary combinations of the components disclosed in the above-described embodiments can form various inventions. For example, some of the all components shown in the embodiments may be omitted. Furthermore, components from different embodiments may be combined as appropriate.
Number | Date | Country | Kind |
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2008-198038 | Jul 2008 | JP | national |