Patent Publication Number: US-8988894-B2

Title: Electronic device

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority benefit of Taiwan application serial no. 101122647, filed on Jun. 25, 2012. The entirety of the above-mentioned patent application is hereby incorporated by reference herein and made a part of this specification. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to an electronic device, and more particularly relates to an electronic device with a loop antenna. 
     2. Description of Related Art 
     As technology advances, electronic devices, such as smart phones, tablet PCs, notebook PCs, etc., are developing to be thinner and lighter. Moreover, in order to draw the attention of the consumers, electronic devices today are mostly equipped with metal back covers to improve the uniqueness and appearance design thereof. 
     For the purpose of miniaturization, the antenna of the electronic device is usually formed directly on an outer surface of a plastic housing by LDS (laser direct structuring) technology, so as to obtain effective radiation space for the antenna. However, such a design requires higher production costs. Besides, due to the appearance design with metallic sense, an additional antenna window needs to be formed on the metal back cover of the electronic device, so that the antenna configured on the metal housing can have better radiation efficiency. However, such a configuration may ruin the overall design of the appearance. 
     In other words, it is a big challenge to design an electronic device that not only satisfies the requirements for miniaturization and appearance design but also reduces production costs and maintains antenna radiation efficiency. 
     SUMMARY OF THE INVENTION 
     The invention provides an electronic device which uses an opening and a metal line in a metal housing to form an excitation path of a loop antenna and utilizes the metal housing to improve the appearance design of the electronic device. 
     The invention provides an electronic device which includes a metal housing, a first opening, a first metal line, a first grounding point, and a first current zero point. The first opening passes through the metal housing. The first metal line is disposed inside the first opening, wherein a first end of the first metal line is electrically connected to a side of the first opening, and a second end of the first metal line includes a first feeding point. The first grounding point and the first current zero point are disposed on the side of the first opening, wherein the metal housing forms a first loop antenna to transmit or receive a first radio frequency signal by a first excitation path from the first feeding point to the first grounding point. 
     In an embodiment of the invention, the electronic device further includes a second opening, a second metal line, a second grounding point, and a second current zero point. The second opening passes through the metal housing. The second metal line is disposed inside the second opening, wherein a first end of the second metal line is electrically connected to a side of the second opening, and a second end of the second metal line includes a second feeding point. The second grounding point and the second current zero point are disposed on the side of the second opening, wherein the metal housing forms a second loop antenna to transmit or receive a second radio frequency signal by a second excitation path from the second feeding point to the second grounding point. 
     In an embodiment of the invention, the metal housing, the first metal line, and the second metal line are integrally formed. 
     Based on the above, the invention uses the opening on the metal housing and the metal line in the opening to form the excitation path of the loop antenna. Accordingly, the metal housing can satisfy the requirement of appearance design, and furthermore the electronic device can utilize the metal housing to receive or transmit radio frequency signals to maintain the radiation efficiency of the antenna. In addition, because the metal housing and the metal line are integrally formed, the appearance quality of the electronic device is further improved and the production costs thereof are reduced. 
     In order to make the aforementioned features and advantages of the invention more comprehensible, several embodiments accompanied with figures are described in detail below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are included to provide further understanding, and are incorporated in and constitute a part of this specification. The drawings illustrate embodiments and, together with the description, serve to explain the principles of the invention. 
         FIG. 1  is a schematic view of a part of an electronic device according to an embodiment of the invention. 
         FIG. 2  illustrates an excitation path of a loop antenna according to an embodiment of the invention. 
         FIG. 3  is a schematic view of a part of an electronic device according to another embodiment of the invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
       FIG. 1  is a schematic view of a part of an electronic device according to an embodiment of the invention. Referring to  FIG. 1 , an electronic device  10  includes a metal housing  100 , a first opening  110 , a first metal line  120 , a first grounding point GP 1 , a first current zero point ZP 1 , and a first feeding point FP 1 . Herein, the first opening  110  passes through the metal housing  100 . The first metal line  120  is disposed inside the first opening  110 . In addition, a first end of the first metal line  120  is electrically connected to a side SD 1  of the first opening  110 , and a second end of the first metal line  120  includes the first feeding point FP 1 . In this embodiment, the metal housing  100  is a back cover of the electronic device  10 , for example, and the first metal line  120  and the metal housing  100  are integrally formed. However, it should be noted that the invention is not limited thereto. 
     The first grounding point GP 1  and the first current zero point ZP 1  are located on the side SD 1  of the first opening  110 . Herein, the metal housing  100  forms a first loop antenna to transmit or receive a first radio frequency signal by a first excitation path EP 1  from the first feeding point FP 1  to the first grounding point GP 1 . Herein, the first loop antenna is a half-wavelength loop antenna, for example, and thus a length of the first excitation path EP 1  is a half of a wavelength of the first radio frequency signal, for example. In addition, it is known from the characteristics of the loop antenna that the first excitation path EP 1  has the first current zero point ZP 1  thereon. 
     For instance,  FIG. 2  illustrates the excitation path of the loop antenna according to an embodiment of the invention. As indicated by the arrow in  FIG. 2 , a current is fed to the half-wavelength loop antenna via the first feeding point FP 1 . Moreover, the current from the first feeding point FP 1  and an excitation current from a system ground plane are reverse to each other. Therefore, the first current zero point ZP 1  is formed on the excitation path from the first feeding point FP 1  to the first grounding point GP 1 . In addition, the first current zero point ZP 1  is located approximately at a center of the first excitation path EP 1 . That is, in this embodiment, a distance from the first current zero point ZP 1  to the first grounding point GP 1  is a quarter of the wavelength of the first radio frequency signal, for example. The first current zero point ZP 1  on the excitation path EP 1  is located near a juncture between the first end of the first metal line  120  and the side SD 1 , for example. 
     It is noted that, in this embodiment, the metal housing  100  is electrically connected to the system ground plane (not shown) in the electronic device  10 . Moreover, in actual application, the electronic device  10  can transmit a signal from the first feeding point FP 1  to a transceiver therein (not shown) via a coaxial line (not shown), wherein an inner conductor of the coaxial line is electrically connected to the first feeding point FP 1 , and an outer conductor of the coaxial line is electrically connected to the system ground plane. Besides using the coaxial line to feed the signal, the electronic device  10  can use a conductive element, such as a contact spring or a pogo pin, to replace the coaxial line and reduce transmission loss of the signal. 
       FIG. 1  illustrates examples of the shapes of the first opening  110  and the first metal line  120  in this embodiment, but it should be noted that the invention is not limited thereto. Persons skilled in the art may adjust the shapes of the first opening  110  and the first metal line  120  according to the frequency and impedance matching of the first radio frequency signal they need. Specifically, the first opening  110  has a rectangular shape or an irregular geometrical shape, and the first metal line  120  has a strip shape or an irregular geometrical shape, for example. 
     In another embodiment of the invention, the electronic device  10  further forms a plurality of loop antennas by the metal housing. For instance,  FIG. 3  is a schematic view of a part of an electronic device according to another embodiment of the invention. In comparison with the embodiment of  FIG. 1 , the electronic device  10  of  FIG. 3  further includes a second opening  210 , a second metal line  220 , a second grounding point GP 2 , a second current zero point ZP 2 , and a second feeding point FP 2 . 
     As shown in  FIG. 3 , the second opening  210  passes through the metal housing  100 . The second metal line  220  is disposed inside the second opening  210 . In addition, a first end of the second metal line  220  is electrically connected to a side SD 2  of the second opening  210 , and a second end of the second metal line  220  includes the second feeding point FP 2 . Accordingly, the metal housing  100  forms a second loop antenna to transmit or receive a second radio frequency signal by a second excitation path EP 2  between the second grounding point GP 2  and the second feeding point FP 2 . In addition, a length of the second excitation path EP 2  is a half of a wavelength of the second radio frequency signal, and a distance from the second current zero point ZP 2  to the second grounding point GP 2  is a quarter of the wavelength of the second radio frequency signal, for example. 
     Similar to the embodiment of  FIG. 1 , the metal housing  100 , the first metal line  120 , and the second metal line are  220  integrally formed. Moreover, persons skilled in the art may adjust the shapes of the second opening  210  and the second metal line  220  according to the frequency and impedance matching of the second radio frequency signal they need. Furthermore, the electronic device  10  can transmit a signal from the second feeding point FP 2  to a transceiver therein through a conductive element, such as a coaxial line, a contact spring, or a pogo pin. 
     It should be noted that the electronic device  10  can form two loop antennas to operate in different frequencies by the first excitation path EP 1  and the second excitation path EP 2 . In an exemplary embodiment of the invention, the metal housing  100  forms the first loop antenna that operates in 2.4 GHz by the first excitation path EP 1  and forms the second loop antenna that operates in 5 GHz by the second excitation path EP 2 , for example. However, it should be noted that the invention is not limited thereto. 
     Further, in another exemplary embodiment of the invention, the electronic device  10  also includes a function module  230 , as illustrated in  FIG. 3 . The function module  230  is a camera module, for example. Herein, the function module  230  is fixed to the metal housing  100  by fastening elements  231  and  232 . It should be noted that, even if the current zero point of the loop antenna is connected to other metal elements nearby, a resonance mode of the loop antenna is not affected. Therefore, the fastening elements  231  and  232  are configured respectively corresponding to the first current zero point ZP 1  and the second current zero point ZP 2 . That is, in actual application, the metal housing  100  further includes two openings (not shown), which respectively pass through the parts of the metal housing  100  that correspond to the first current zero point ZP 1  and the second current zero point ZP 2 . Accordingly, the fastening elements  231  and  232  respectively pass through the two openings to fix the function module  230  to the metal housing  100 . 
     It is worth mentioning that, in the embodiment of  FIG. 3 , the electronic device  10  further includes decorative thin films  240  and  250  to improve the appearance design of the electronic device  10 . The decorative thin films  240  and  250  respectively fill the first opening  110  and the second opening  210 . Moreover, the decorative thin films  240  and  250  can be formed to have an appearance of metallic sense, so as to maintain the uniformity of the appearance of the metal housing  100 . 
     In conclusion of the above, the invention provides an electronic device that uses the opening on the metal housing and the metal line in the opening to form the excitation path of the loop antenna. Accordingly, the metal housing satisfies the requirement of appearance design, and furthermore the electronic device can utilize the metal housing to receive or transmit radio frequency signals to maintain the radiation efficiency of the antenna. The combination of the antenna and the housing also helps miniaturize the electronic device. In addition, because the metal housing and the metal line are integrally formed, the appearance quality of the electronic device is further improved and the production costs thereof are reduced. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the disclosed embodiments without departing from the scope or spirit of the disclosure. In view of the foregoing, it is intended that the disclosure covers modifications and variations of this disclosure provided that they fall within the scope of the following claims and their equivalents.