Patent Publication Number: US-2012026057-A1

Title: Antenna device

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2010-172209, filed Jul. 30, 2010; the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to an antenna device applied to, for example, a personal computer with a wireless communication function. 
     BACKGROUND 
     In recent years, an easy-to-carry, battery-powered, notebook-size personal computer has become widely used. Public wireless local area network (LAN) services known as hot spot services are beginning to be offered in various regions. Against this background, many personal computers of this type include a wireless communication function of executing wireless communication with a wireless LAN access point (AP). In addition, nowadays, it is becoming common practice for a personal computer to be equipped with a wireless communication function of executing wireless communication with an external device according to a third-generation (3G) mobile communication method. 
     As the number of types of wireless communication methods increases, the wireless communication functions of personal computers of this type are required to support a plurality of wireless communication methods. To meet the requirement, various mechanisms for covering a plurality of resonant frequency bands with a single antenna (for multiple resonance) have been proposed. 
     For example, an antenna device that covers three resonant frequency bands is well known. The antenna device includes a first antenna element connected to a feeding point and a second antenna element connected to the first antenna element at a point located near the feeding point. In the antenna device with such a configuration, (1) antenna current flows mostly over the first antenna element at a first resonant frequency, (2) antenna current flows mostly over the second antenna element at a second resonant frequency, and (3) antenna current flows mostly over the first antenna element at a third resonant frequency. The third resonant frequency is a triple harmonic of the first resonant frequency. 
     Therefore, when the length of the first antenna element is changed, not only the first resonant frequency but also the third resonant frequency changes. That is, an antenna device with the aforementioned configuration has the problem of being incapable of adjusting the first and third resonant frequencies independently. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       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. 
         FIG. 1  is an exemplary view showing an external appearance of an information processing apparatus equipped with an antenna device according to an embodiment. 
         FIG. 2  is an exemplary view showing a system configuration of the information processing apparatus equipped with the antenna device of the embodiment. 
         FIG. 3  is an exemplary view showing a configuration of the antenna device according to the embodiment. 
         FIG. 4  is an exemplary view showing a characteristic (VSWR) of the antenna device according to the embodiment. 
         FIG. 5  is an exemplary view showing a configuration of a general antenna device. 
         FIG. 6  is an exemplary view showing a characteristic (VSWR) of the general antenna device. 
         FIG. 7  is an exemplary view showing current distribution for an antenna element at each resonant frequency in the general antenna device. 
         FIG. 8  is an exemplary view showing current distribution for the antenna element at each resonant frequency in an antenna device of the embodiment. 
         FIG. 9  is an exemplary view showing a characteristic (VSWR) of the antenna device of the embodiment when the length of each element is changed. 
         FIG. 10  is an exemplary diagram to explain a first element length, a second element length, and a third element length in  FIG. 9 . 
         FIG. 11  is an exemplary diagram to explain the way a second resonant frequency is replaced with a third resonant frequency in the antenna device of the embodiment. 
         FIG. 12  is an exemplary view showing a first modification of the configuration of the antenna device of the embodiment. 
         FIG. 13  is an exemplary view showing a second modification of the configuration of the antenna device of the embodiment. 
         FIG. 14  is an exemplary view showing a third modification of the configuration of the antenna device of the embodiment. 
         FIG. 15  is an exemplary view showing a fourth modification of the configuration of the antenna device of the embodiment. 
         FIG. 16  is an exemplary view showing a fifth modification of the configuration of the antenna device of the embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments will be described hereinafter with reference to the accompanying drawings. 
     In general, according to one embodiment, an antenna device includes a linear first antenna element, a linear second antenna element and a linear third antenna element. One end of the first antenna element is connected to a feeding point. One end of the second antenna element is connected to the feeding point. A length of the second antenna element is shorter than a length of the first antenna element. One end of the third antenna element is connected onto the first antenna element. A length of the third antenna element is shorter than the length of the first antenna element. 
       FIG. 1  is an exemplary view showing an external appearance of an information processing apparatus equipped with an antenna device according to an embodiment. The information processing apparatus is realized by, for example, a battery-powered portable personal computer  10 . 
       FIG. 1  is an exemplary perspective view of the computer  10 , with its display unit opened. The computer  10  includes a computer main body  11  and a display unit  12 . A liquid-crystal display (LCD)  17  is incorporated in the display unit  12 . The display screen of the LCD  17  is located roughly in the center of the display unit  12 . 
     The display unit  12  is arranged on the computer main body  11  so as to turn freely via a hinge unit  20 . The hinge unit  20  is a coupling unit that couples the display unit  12  with the computer main body  11 . That is, the display unit  12  is supported by the hinge unit  20  arranged at the back-end part of the computer main body  11 . The display unit  12  is arranged on the computer body with the hinge unit  20  so as to turn freely between an open position at which the top face of the computer main body  11  is exposed and a closed position at which the top face of the computer body is covered with the display unit  12 . 
     The antenna device  1  of the embodiment is arranged in the display unit  12 . The antenna device  1  covers a first to a third resonance frequency band. A signal line  2  directed from a wireless communication module  112  arranged in the computer main body  11  into the display unit  12  via the hinge unit  2  is connected to the antenna device  1 . 
     The computer main body  11  is a base unit that has a thin box chassis. On the top face of the computer main body  11 , there are arranged a keyboard  13 , a power button  14  for turning on and off the computer  10 , an input operation panel  15 , a touchpad  16 , speakers  18 A,  18 B, and others. On the input operation panel  15 , various operation buttons are arranged. In the computer main body  11 , there is arranged a system board (also referred to as a motherboard) on which various electronic parts are mounted. The wireless communication module  112  is arranged on the system board. The wireless communication module  112  is a module that executes wireless communication with an external device according to, for example, a third-generation (3G) mobile communication method. 
     The mounting position of the antenna device  1  is, for example, in the top end part of the display unit  12 . Arranging the antenna device  1  in the top end part of the display unit  12  enables the wireless communication module  112  to execute wireless communication with an external device, with the antenna device  1  located in a relatively high position. 
     On the right side surface of the computer main body  11 , there is arranged a Universal Serial Bus (USB) connector  19  for connecting a USB cable or a USB device complying with, for example, the USB 2.0 standard. 
       FIG. 2  is an exemplary view showing a system configuration of the computer  10 . 
     As shown in  FIG. 2 , the computer  10  includes a central processing unit (CPU)  101 , a north bridge  102 , a main memory  103 , a south bridge  104 , and a graphic processing unit (GPU)  105 . The computer  10  further includes a video random access memory (VRAM)  105 A, a sound controller  106 , a Basic Input/Output System read-only memory (BIOS-ROM)  107 , a LAN controller  108 , a hard disk drive (HDD)  109 , and an optical disc drive (ODD)  110 . The computer  10  further includes a USB controller  111 , a wireless communication module  112 , various peripheral devices  113 , an embedded controller/keyboard controller (EC/KBC)  114 , and an electrically erasable programmable ROM (EEPROM)  115 . 
     The CPU  101  is a processor that controls the operation of each component of the computer  10 . The CPU  101  executes an operating system (OS) and various application programs loaded from the HDD  109  into the main memory  103 . The CPU  101  further executes a BIOS stored in the BIOS-ROM  107 . The BIOS is a program for hardware control. 
     The north bridge  102  is a bridge device that connects a local bus of the CPU  101  and the south bridge  104 . The north bridge  102  includes a memory controller that executes access control of the main memory  103 . The north bridge  102  includes the function of communicating with the GPU  105  via a serial bus or the like conforming to, for example, the PCI EXPRESS standard. 
     The GPU  105  is a display controller that controls the LCD  17  used as a display monitor of the computer  10 . A display signal generated by the GPU  105  is sent to the LCD  17 . 
     The south bridge  104  controls the various peripheral devices  113  on a Peripheral Component Interconnect (PCI) bus. The south bridge  104  includes an Integrated Drive Electronics (IDE) controller for controlling the HDD  109  and ODD  110 . In addition, the south bridge  104  includes the function of communicating with the LAN controller  108 , USB controller  111 , and the wireless communication module  112 . 
     The sound controller  106 , which is a sound source device, outputs audio data to be reproduced to the speakers  18 A,  18 B. The LAN controller  108  is a wired communication device that executes wire communication complying with, for example, the IEEE 802.3 standard. The USB controller  111  executes communication with an external device (which is connected via the USB connector  19 ) conforming to, for example, the USB 2.0 standard. 
     The wireless communication module  112  includes an antenna terminal for transmitting and receiving a radio-frequency (RF) signal. The signal line  2  is connected to the antenna terminal. The wireless communication module  112  is coupled with the antenna device  1  via the signal line  2 . 
     The EC/KBC  114  is a single-chip microcomputer into which an embedded controller for power management and a keyboard controller for controlling the keyboard  13  and touchpad  16  have been integrated. The EC/KBC  114  includes the function of turning on or off the computer  10  according to the user operation of the power button  14 . 
     Next, the configuration of the antenna device  1  of the embodiment mounted on the computer  10  which has the aforementioned system configuration will be explained.  FIG. 3  is an exemplary view showing a configuration of the antenna device  1 . 
     In  FIG. 3 , reference numbers  201 ,  202 ,  203  indicate antenna elements. Reference number  201  is referred to as a first element,  202  as a second element, and  203  as a third element. Reference number  204  indicates a feeding point and  205  an antenna ground (earth conductor: GND). 
     As shown in  FIG. 3 , in the antenna device  1 , the first element  201  and second element  202  are connected to the feeding point  204 . In addition, the third element  203  is connected to the first element  201  connected to the feeding point  204  at a branch point x. The antenna device  1  includes the third element  203  added to a halfway point (branch point x) of the first element  201 , thereby enabling the first to third resonant frequencies to be adjusted independently. This will be explained in detail below. 
     The length of each of the first element  201 , second element  202 , and third element  203  is set so as to satisfy the following requirements (1 to 3): (1) the length of the first element is about ¼ the wavelength of the first resonant frequency, (2) the length of the second element is about ¼ the wavelength of the second resonant frequency, and (3) the length from the tip of the first element to the tip of the third element via the branch point x is about ½ the wavelength of the third resonant frequency. 
       FIG. 4  is an exemplary view showing a characteristic (VSWR) of the antenna device  1 . In  FIG. 4 , the abscissa represents frequency and the ordinate represents VSWR. 
     As described above, the antenna device  1  covers the first to third resonant frequency bands. In  FIG. 4 , ( 1 ) indicates the first resonant frequency, ( 2 ) the second resonant frequency, and ( 3 ) the third resonant frequency. 
     The configuration of a general antenna device which covers a first to a third resonant frequency band (without a third element) is shown in  FIG. 5  in comparison with the antenna device  1  of the embodiment. A characteristic (VSWR) of the general antenna device is shown in  FIG. 6 . In  FIG. 5 , the same modules as those in the antenna device  1  of the embodiment are indicated by the same reference numbers. As in the antenna device  1  of the embodiment shown in  FIG. 4 , in  FIG. 6 , ( 1 ) indicates the first resonant frequency, ( 2 ) the second resonant frequency, and ( 3 ) the third resonant frequency. 
       FIG. 7  is an exemplary view showing current distribution for the antenna element at each resonant frequency in the general antenna device (without a third element). In  FIG. 7 , “A” shows current distribution at the first resonant frequency, “B” shows current distribution at the second resonant frequency, and “C” shows current distribution at the third resonant frequency. An (dashed) arrow indicates the direction of current. 
     As shown in  FIG. 7 , at the first resonant frequency [A], current flow for the general antenna device is mostly over the first element  201 . At the second resonant frequency [B], current flow for the general antenna device is mostly over the second element  202 . At the third resonant frequency [C], current flow for the general antenna device is mostly over the first element  201 . The third resonant frequency is a triple harmonic of the first resonant frequency. 
     Therefore, when the length of the first element  201  is changed, not only the first resonant frequency but also the third resonant frequency changes. That is, the general antenna device cannot adjust the first resonant frequency and third resonant frequency independently. 
       FIG. 8  is an exemplary view showing current distribution for the antenna element at each resonant frequency in the antenna device  1  of the embodiment (with the third element  203  added). In  FIG. 8 , “A” shows current distribution at the first resonant frequency, “B” shows current distribution at the second resonant frequency, and “C” shows current distribution at the third resonant frequency. The (dashed) arrow indicates the direction of the current. 
     As shown in  FIG. 8 , at the first resonant frequency [A], current flow for the antenna device  1  is mostly over the first element  201 . At the second resonant frequency [B], current flow for the antenna device  1  is mostly over the second element  202 . At the third resonant frequency [C], current flow for the antenna device  1  is mostly over the first element  201  and third element  203 . 
       FIG. 9  is an exemplary view showing a characteristic (VSWR) of the antenna device  1  of the embodiment when the length of each of the elements ( 201 ,  202 ,  203 ) is changed. In  FIG. 9 , “first element length,” “second element length,” and “third element length” refer to the length of the first element  201 , second element  202 , and third element  203 , respectively, as shown in  FIG. 10 . 
     In  FIG. 9 , “A” indicates a case where only the length of the first element  201  was changed, “B” indicates a case where only the length of the second element  202  was changed, “C” indicates a case where only the length of the third element  203  was changed. In  FIG. 9 , suppose the distance from the tip of the first element  201  to the branch point to which the third element  203  is connected is 42 mm. 
     As shown in “A” of  FIG. 9 , when only the length of the first element  201  (“first element length”) was changed, the first resonant frequency and third resonant frequency mostly change. As shown in “B” of  FIG. 9 , when only the length of the second element  202  (“second element length”) was changed, only the second resonant frequency mostly changes. As shown in “C” of  FIG. 9 , when only the length of the third element  203  (“third element length”) was changed, only the third resonant frequency mostly changes. 
     Therefore, with the configuration of the antenna device  1  of the embodiment (to which the third element  203  has been added), the first to third resonant frequencies can be adjusted independently by adjusting the length of each of the elements ( 201 ,  202 ,  203 ). 
     The length of the first element  201  is about ¼ the wavelength of the first resonant frequency, the length of the second element  202  is about ¼ the wavelength of the second resonant frequency, and the length from the tip of the first element  201  to the tip of the third element  203  via the branch point x is about ½ the wavelength of the third resonant frequency. 
     Next, a case where the second resonant frequency is made higher than the third resonant frequency will be explained with reference to  FIG. 11 . 
     As shown in “A” of  FIG. 11 , let the length of the first element  201  be 82 mm, the length of the second element  202  be 34 mm, the length of the third element  203  be 35 mm, and the distance from the tip of the first element  201  to the branch point x to which the third element  302  has been connected be 42 mm. In this case, a characteristic (VSWR) of the antenna device  1  is shown in “B” of  FIG. 11 . In “B” of  FIG. 11 , ( 1 ) indicates a first resonant frequency, ( 2 ) a second resonant frequency, and ( 3 ) a third resonant frequency. 
     As shown in “B” of  FIG. 11 , the first resonant frequency generated by the first element  201  appears mostly at about 800 MHz. The second resonant frequency generated by the second element  202  appears mostly at about 2.1 GHz. The third resonant frequency generated by the third element  203  appears mostly at about 1.8 GHz. 
     In the case of  FIG. 11 , too, the length of the first element  201  is about ¼ the wavelength of the first resonant frequency, the length of the second element  202  is about ¼ the wavelength of the second resonant frequency, and the length from the tip of the first element  201  to the tip of the third element  203  via the branch point x is about ½ the wavelength of the third resonant frequency. 
     As described above, with the antenna device  1  of the embodiment, the second resonant frequency and the third resonant frequency can be replaced with each other by adjusting the length of the second element  202  and that of the third element  203 . 
     Therefore, with the antenna device  1  of the embodiment, the first to third resonant frequencies can be adjusted independently by adding the third element  203  to a halfway point (or branch point x) of the first element  201 . That is, a small, easy-to-adjust antenna device  1  can be realized. 
     While in the explanation, the configuration of  FIG. 3  has been shown as a configuration of the antenna device  1  of the embodiment where the third element  203  has been added to a halfway point (branch point x) of the first element  201 , it is not limited to this and may be modified in various ways. 
     For example, as shown in  FIG. 12 , the first element  201  may be bent at a branch point x with the third element  203  in a direction in which the element  201  gets away from GND  205  and then, for example, the third element  203  may be located at the collinear position as the unbent first element  201 . In this case, the first element  201  can be separated from GND  205 , enabling the antenna characteristic to be improved at about the first resonant frequency. 
     In addition, as shown in  FIG. 13 , the tip portion of the first element  201  may be further bent inward so as to enclose, for example, the third element  203 . That is, the tip portion of the first element  201  may be formed into a U shape. In this case, the antenna can be shortened in the width direction, enabling the antenna device  1  to be made more compact. 
     Furthermore, as shown in  FIG. 14 , the first element  201  and second element  203  may be stacked one on top of the other in a direction of antenna thickness. In this case, both of the tips of the first element  201  and third element  203  can be located away from GND  205 , enabling the antenna characteristic to be improved. 
     Moreover, as shown in  FIG. 15 , the first element  201  may be configured to have a turned-back structure (a so-called turned-back antenna). In this case, the impedance can be increased at about the first resonant frequency. Even when the distance between the first element  201  and GND  205  is short, a decrease in the impedance can be alleviated, enabling the antenna characteristic to be improved. In this case, the third element  203  may be arranged on the GND side as shown in “B” of  FIG. 15 . 
     Still furthermore, as shown in  FIG. 16 , like a so-called inverted F antenna, a short-circuit part to GND  205  may be arranged on the first element  201  for impedance adjustment. 
     The various modules of the systems described herein can be implemented as software applications, hardware and/or software modules, or components on one or more computers, such as servers. While the various modules are illustrated separately, they may share some or all of the same underlying logic or code. 
     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.