Patent Publication Number: US-2012032856-A1

Title: Planar antenna

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority of Taiwanese Application No. 099214905, filed on Aug. 4, 2010. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a planar antenna, more particularly to a planar antenna with transverse coupling. 
     2. Description of the Related Art 
     Planar inverted-F antenna (PIFA) has advantages of being flat, lightweight, etc., and is therefore suitable for mobile phones, Bluetooth devices, radio frequency devices and so on. 
     Referring to  FIG. 1 , Taiwanese Patent No. 1318021 discloses a broadband planar antenna  900 , wherein a coupling conductor  920  is fed with signals from a feed-in line  910 , and signals may be coupled to an extension conductor  930  adjacent to the coupling conductor  920  for resonation in a high frequency band. However, there is longitudinal coupling between the coupling conductor  920  and the extension conductor  930 , i.e., extension direction and coupling direction of the coupling conductor  920  and the extension conductor  930  are substantially parallel, such that a length of the coupling conductor  920  may directly affect coupling amount of signals coupled to the extension conductor  930  (under the condition that a gap between the coupling conductor  920  and the extension conductor  930  is kept the same). Thus, when designers want to modify the length of the coupling conductor  920  according to different usage demands, the coupling amount between the coupling conductor  920  and the extension conductor  930  may be undesirably changed therewith so that the bandwidth of the broadband planar antenna  900  is not easy to control. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide a planar antenna with increased bandwidth and easily-configured operation mode. 
     Accordingly, a planar antenna of the present invention is to be laid out on a circuit board, and includes a grounding part, a first radiator arm and a second radiator arm. The first radiator arm is spaced apart from the grounding part, and includes a first coupling section and a feed-in end. The second radiator arm includes an extension section and a second coupling section. The extension section has one end connected to the grounding part, and further has another end connected to the second coupling section. The first coupling section extends in a first direction substantially perpendicular to a second direction in which the second coupling section extends. The first coupling section is spaced apart from the second coupling section such that signals transmitted through the first coupling section may be coupled to the second coupling section. In this way, when length of the first radiator arm or the second radiator arm is changed, coupling amount between the first radiator arm and the second radiator arm may be kept the same to facilitate configuration of the operating frequency band of the planar antenna. 
     Preferably, the first radiator arm further includes a first arm section, a second arm section, and a third arm section. The first arm section is spaced apart from the grounding part, and has one end which is adjacent to the grounding part and which serves as the feed-in end. The first arm section extends in the first direction. The second arm section has one end connected to another end of the first arm section opposite to the feed-in end, and extends in the second direction. The first coupling section has one end connected to another end of the second arm section opposite to the first arm section, and extends in the first direction. The third arm section has one end connected to another end of the first coupling section opposite to the second arm section, and extends in the second direction. Therefore, amount of transverse coupling between the first coupling section and the second coupling section is unaffected by a change in the length of any one of the first arm section, the second arm section, the third arm section, and the first coupling section. Thus, it is easier to configure the operating frequency band of the planar antenna. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other features and advantages of the present invention will become apparent in the following detailed description of the five preferred embodiments with reference to the accompanying drawings, of which: 
         FIG. 1  illustrates a conventional broadband planar antenna; 
         FIG. 2  illustrates a first preferred embodiment of the planar antenna of the present invention; 
         FIG. 3  illustrates actual dimensions of the planar antenna of the first preferred embodiment; 
         FIG. 4  illustrates that a first radiator arm of the first preferred embodiment may resonate in a first frequency band, wherein arrows in  FIG. 4  indicate a transmission direction of input signals; 
         FIG. 5  illustrates that a second radiator arm of the first preferred embodiment may resonate in a second frequency band, wherein arrows in  FIG. 5  indicate another transmission direction of the input signals; 
         FIG. 6  illustrates a Voltage Standing Wave Ratio plot (VSWR) of the planar antenna of the first preferred embodiment; 
         FIG. 7  illustrates a second preferred embodiment of the planar antenna of the present invention; 
         FIG. 8  illustrates a VSWR plot of the planar antenna of the second preferred embodiment; 
         FIG. 9  illustrates a third preferred embodiment of the planar antenna of the present invention; 
         FIG. 10  illustrates a VSWR plot of the planar antenna of the third preferred embodiment; 
         FIG. 11  illustrates a fourth preferred embodiment of the planar antenna of the present invention; 
         FIG. 12  illustrates a VSWR plot of the planar antenna of the fourth preferred embodiment; 
         FIG. 13  illustrates a fifth preferred embodiment of the planar antenna of the present invention; 
         FIG. 14  illustrates a first surface of a circuit board of the fifth preferred embodiment, wherein a second radiator arm and a third coupling section are laid out thereon; 
         FIG. 15  illustrates a second surface of the circuit board of the fifth preferred embodiment, wherein a first arm section, a second arm section, a first coupling section and a third arm section are laid out thereon; and 
         FIG. 16  illustrates a VSWR plot of the planar antenna of the fifth preferred embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Before the present invention is described in greater detail with reference to the preferred embodiments, it should be noted that the same reference numerals are used to denote the same elements throughout the following description. 
     Referring to  FIG. 2 , a first preferred embodiment of a planar antenna  100  of the present invention is illustrated. The planar antenna  100  is laid out on one surface of a printed circuit board (PCB)  4 , and includes a first radiator arm  1 , a second radiator arm  2  and a grounding part  3 . An extension direction of at least a portion of the first radiator arm  1  is substantially transverse to an extension direction of at least a portion of the second radiator arm  2 , such that signals transmitted through the first radiator arm  1  may be coupled transversely to the second radiator arm  2  for achieving an effect of increased bandwidth. 
     The first radiator arm  1  includes a first arm section  11 , a second arm section  12 , a first coupling section  10 , and a third arm section  13 . The first arm section  11  is spaced apart from the grounding part  3 , and extends in a first direction (Y-axis direction). The first arm section  11  has one end which is adjacent to the grounding part  3  and which serves as a feed-in end  5 . The second arm section  12  has one end connected to another end of the first arm section  11  distal from the grounding part  3  (i.e., another end of the first arm section  11  opposite to the feed-in end  5 ), and extends in a second direction (X-axis direction). The first direction is substantially perpendicular to the second direction. 
     The first coupling section  10  has one end connected to another end of the second arm section  12  opposite to the first arm section  11 , and extends in the first direction. The third arm section  13  has one end connected to another end of the first coupling section  10  opposite to the second arm section  12 , and extends in the second direction. The third arm section  13  is laid out at a long side of the PCB  4 . In this embodiment, an overall length of the first coupling section  10  and the third arm section  13  is greater than that of the first arm section  11  and the second arm section  12 , but is not limited to the disclosure of this embodiment. 
     The second radiator arm  2  includes an extension section  21  and a second coupling section  20 . The extension section  21  has one end connected to the grounding part  3 , and extends in the first direction. The extension section  21  is laid out at a short side of the PCB  4 . The second coupling section  20  has one end connected to another end of the extension section  21  opposite to the grounding part  3 , and extends in the second direction. In this embodiment, an extension direction (second direction) of the second coupling section  20  is transverse to that (first direction) of the first coupling section  10 , and the second coupling section  20  has another end, which is opposite to the extension section  21 , spaced apart from the first coupling section  10  by a predefined gap so that signals transmitted through the first coupling section  10  may be coupled to the second coupling section  20 . 
     Referring to  FIG. 3 , actual dimensions of the planar antenna  100  of this embodiment are illustrated. Units of numerals in  FIG. 3  are in millimeters (mm). A minimum gap between the first coupling section  10  and the second coupling section  20  is smaller than 3 mm (in this embodiment, it is 0.4 mm). Moreover, dimensions of the first radiator arm  1 , the second radiator arm  2  and the grounding part  3  are not limited to the disclosure of this embodiment, and may vary according to different demands. 
     Referring to  FIG. 4  and  FIG. 5 , the planar antenna  100  of this embodiment may resonate in a first frequency band (low frequency) through a first electric current path ( FIG. 4 ) formed by the first radiator arm  1  (the first arm section  11 , the second arm section  12 , the first coupling section  10  and the third arm section  13 ), and may further resonate in a second frequency band (high frequency) through a second electric current path ( FIG. 5 ) formed by the second radiator arm  2  (the extension section  21  and the second coupling section  20 ) for receiving and radiating signals in the corresponding frequency bands. Specifically, since the first coupling section  10  and the second coupling section  20  are spaced apart from each other, signals transmitted through the first coupling section  10  may be coupled to the second coupling section  20  for increasing a bandwidth of the first frequency band (low frequency). Furthermore, the extension direction of the first coupling section  10  is transverse to that of the second coupling section  20  so that the first coupling section  10  and the second coupling section  20  are coupled transversely with each other. Therefore, an amount of transverse coupling between the first coupling section  10  and the second coupling section  20  is unaffected by a change in the length of any one of the first arm section  11 , the second arm section  12 , the third arm section  13 , and the first coupling section  10 . Thus, it is easier to configure the operation mode of the planar antenna  100 . 
     Referring to  FIG. 6 , a voltage standing wave ratio (VSWR) plot of the planar antenna  100  of this preferred embodiment is illustrated. It is apparent from the plot that the VSWR values of the planar antenna  100  are smaller than 3 in the first frequency band and the second frequency band, thus satisfying usage demands. 
     Referring to  FIG. 7 , a second preferred embodiment of the planar antenna  100  of the present invention is illustrated, which is substantially similar to the first embodiment. The differences reside in that the end of the second coupling section  20  of the second radiator arm  2  which is opposite to the extension section  21  further extends in the first direction such that a gap between said end of the second coupling section  20  and the second arm section  12  of the first radiator arm  1  is smaller than that in the first preferred embodiment. Thus, signals may not only be coupled transversely to the second coupling section  20  when transmitted through the first coupling section  10  but may also be coupled longitudinally to the second coupling section  20  when transmitted through the second arm section  12 . In this way, aside from permitting configuration of the operation mode of the planar antenna  100 , radiation efficiency at the first frequency band may be increased. 
     Referring to  FIG. 8 , a VSWR plot of the planar antenna  100  of this embodiment is illustrated. It is apparent from the plot that an operation band of the first frequency band satisfies usage demands in a frequency band ranging from 824 MHz to 960 MHz. 
     Referring to  FIG. 9 , a third preferred embodiment of the planar antenna  100  of the present invention is illustrated, which is substantially similar to the second embodiment. The differences reside in that the extension section  21  of the second radiator arm  2  includes a first segment  211 , a second segment  212 , and a third segment  213 . The first segment  211  has one end connected to the grounding part  3 , and extends in the first direction. The second segment  212  has one end connected to another end of the first segment  211  opposite to the grounding part  3 , and extends in the second direction. The third segment  213  has two ends each connected to a respective one of another end of the second segment  212  opposite to the first segment  211  and one end of the second coupling section  20  distal from the first coupling section  10 . The third segment  213  extends in the first direction. Thus, a length of the second radiator arm  2  may be varied to satisfy demands for operating in different frequency bands. Specifically, in this embodiment, an amount of transverse coupling between the first coupling section  10  and the second coupling section  20  is kept the same for achieving an effect of easily-configurable operation mode of the present invention, even though the length of the second radiator arm  2  has been changed to meet different demands. Referring to  FIG. 10 , a VSWR plot of the planar antenna  100  of this embodiment is illustrated. 
     Referring to  FIG. 11 , a fourth preferred embodiment of the planar antenna  100  of this invention is illustrated. In this embodiment, the first radiator arm  1  includes a first arm section  11 ′, a first coupling section  10 , a second arm section  12 ′, a third arm section  13 ′, and a fourth arm section  14 ′. 
     The first arm section  11 ′ is spaced apart from the grounding part  3 , has one end which is adjacent to the grounding part  3  and which serves as the feed-in end  5 , and extends in the first direction. The first coupling section  10  has one end connected to another end of the first arm section  11 ′ opposite to the feed-in end  5 , and extends in the first direction. The second arm section  12 ′ has one end connected to another end of the first coupling section  10  opposite to the first arm section  11 ′, and extends in the second direction. The third arm section  13 ′ has one end connected to another end of the second arm section  12 ′ opposite to the first coupling section  10 , and extends in the first direction. The fourth arm section  14 ′ has one end connected to another end of the third arm section  13 ′ opposite to the second arm section  12 ′, and extends in the second direction. The fourth arm section  14 ′ has another end spaced apart from the first arm section  11 ′. In this embodiment, the second arm section  12 ′ and the third arm section  13 ′ are respectively laid out at the long side and another short side of the PCB  4 . Similarly, an amount of transverse coupling between the first coupling section  10  and the second coupling section  20  may be kept the same for achieving an effect of easily-configurable operation mode of the planar antenna  100  of the present invention, even though a length of the first radiator arm  1  has been changed to meet different demands. Referring to  FIG. 12 , a VSWR plot of the planar antenna  100  of this embodiment is illustrated. 
     Referring to  FIG. 13 , a fifth preferred embodiment of the planar antenna  100  of the present invention is illustrated, which is substantially similar to the second embodiment. The differences reside in that aside from a first arm section  11 , a second arm section  12 , a first coupling section  10  and a third arm section  13 , the first radiator arm  1  of this embodiment further includes a third coupling section  30 . 
     Referring to  FIG. 14  and  FIG. 15 , the third coupling section  30  of the first radiator arm  1  is laid out on a first surface of the PCB  4 . The first arm section  11 , the second arm section  12 , the first coupling section  10  and the third arm section  13  are laid out on a second surface (opposite to the first surface on which the third coupling section  30  is laid out) of the PCB  4 , and connecting relations thereby are the same as those in the second preferred embodiment. Thus, further details of the same are omitted herein for the sake of brevity. 
     The second radiator arm  2  includes an extension section  21  and a second coupling section  20 , and connecting relation therebetween is the same as that in the second preferred embodiment. 
     The third coupling section  30  is disposed between the second coupling section  20  and the grounding part  3 , and is spaced apart from the second coupling section  20  and the grounding part  3 . The third coupling section  30  has one end, which is adjacent to the grounding part  3  and which serves as the feed-in end  5  of the planar antenna  100  of this preferred embodiment. While the third coupling section  30  overlaps with a projection of the first arm section  11  onto the first surface completely and with a portion of a projection of the second arm section  12  onto the first surface, the present invention is not limited in this respect as long as the third coupling section  30  overlaps with at least a portion of the projection of the first arm section  11  onto the first surface. 
     When the feed-in end  5  is fed with signals, the signals transmitted through the third coupling section  30  may be coupled to the first arm section  11 , and transmitted to the third arm section  13  via the second arm section  12  and the first coupling section  10  so as to resonate in the first frequency band. Specifically, signals transmitted through the first coupling section  10  may be coupled to the second coupling section  20  with the same amount of transverse coupling for increasing the bandwidth of the first frequency band. Thus, the effect of easily-configurable operation mode of the planar antenna  100  of the present invention may be likewise achieved. Referring to  FIG. 16 , a VSWR plot of the planar antenna  100  of this embodiment is illustrated. 
     In summary, an operation bandwidth of the planar antenna  100  of the present invention may be increased by virtue of the extension direction of at least a portion of the first radiator arm  1  being substantially transverse to the extension direction of at least a portion of the second radiator arm  2 , such that signals transmitted through the first radiator arm  1  may be coupled transversely to the second radiator arm  2 . Moreover, the amount of transverse coupling between the first coupling section  10  and the second coupling section  20  is unaffected by a change in the lengths of the first coupling section  10  and the second coupling section  20 . Thus, it is easier to configure the operation mode of the planar antenna  100 . 
     While the present invention has been described in connection with what are considered the most practical and preferred embodiments, it is understood that this invention is not limited to the disclosed embodiments but is intended to cover various arrangements included within the spirit and scope of the broadest interpretation so as to encompass all such modifications and equivalent arrangements.