Patent Publication Number: US-2015061952-A1

Title: Broadband Antenna

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a broadband antenna, and more particularly, to a broadband antenna in which passive elements are utilized to excite a resonance effect of the antenna, thereby increasing the bandwidth of a high frequency band and improving the impedance matching of the antenna in a low frequency band. 
     2. Description of the Prior Art 
     Antennas are widely used in electronic products to emit or receive radio waves for conveying or exchanging wireless signals. Generally, electronic products with wireless communication functionalities, such as laptops, tablet PCs, personal digital assistants (PDAs), mobile phones and wireless base stations, utilize embedded antennas to access wireless networks. In order to let the users access wireless communication networks more conveniently, the antenna bandwidth should be as broad as possible so that more communication protocols can be complied with, while the antenna size should be minimized to meet the downsizing trend of electronic products. With the evolution of wireless communication technology, it has become a basic requirement for a wireless communication system to send and receive large amounts of data. Since different wireless communication protocols may have different operational frequency bands, it is desirable that a single antenna can support multiple operational frequency bands for different wireless communication protocols. 
     Therefore, how to design a miniature antenna which has broad bandwidth for complying with the operational frequency band requirements of different wireless communication protocols is an important topic to be addressed and discussed. 
     SUMMARY OF THE INVENTION 
     An objective of the present invention is to provide an antenna which utilizes passive elements in the proximity of the feed-in point of the antenna, thereby improving the bandwidth and reducing the antenna dimension. 
     An embodiment of the present invention discloses a broadband antenna used for a wireless transceiver. The broadband antenna includes a grounding unit for grounding; a radiating part; a signal feed-in element for transmitting a radio signal to the radiating part in order to emit the radio signal via the radiating part, wherein a grounding terminal of the signal feed-in element is electrically connected to the grounding unit; a feed-in point located on the radiating part; a capacitor electrically connected between the feed-in point and the signal feed-in element; and a first inductor having a first terminal electrically connected to the capacitor. 
     These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a schematic diagram of a broadband antenna according to an embodiment of the present invention. 
         FIG. 1B  illustrates a plane of the broadband antenna shown in  FIG. 1A . 
         FIG. 1C  illustrates another plane of the broadband antenna shown in  FIG. 1A . 
         FIG. 1D  illustrates a vertical section of the broadband antenna shown in  FIG. 1A . 
         FIG. 1E  is a diagram of a voltage standing wave radio (VSWR) of the broadband antenna shown in  FIG. 1A . 
         FIG. 1F  is a diagram of a radiation efficiency of the broadband antenna shown in  FIG. 1A . 
         FIG. 2  is a schematic diagram of a broadband antenna according to an embodiment of the present invention. 
         FIG. 3A  is a schematic diagram of a broadband antenna according to an embodiment of the present invention. 
         FIG. 3B  illustrates a plane of the broadband antenna shown in  FIG. 3A . 
         FIG. 3C  illustrates another plane of the broadband antenna shown in  FIG. 3A . 
         FIG. 4  is a schematic diagram of a broadband antenna according to an embodiment of the present invention. 
         FIG. 5  is a schematic diagram of a broadband antenna according to an embodiment of the present invention. 
         FIG. 6  is a schematic diagram of a wireless communication device equipped with the broadband antenna shown in  FIG. 1A . 
     
    
    
     DETAILED DESCRIPTION 
     Please refer to  FIGS. 1A to 1F , where  FIG. 1A  is a schematic diagram of a broadband antenna  10  according to an embodiment of the present invention,  FIG. 1B  illustrates a plane of the broadband antenna  10 ,  FIG. 1C  illustrates another plane of the broadband antenna  10 ,  FIG. 1D  illustrates a vertical section of the broadband antenna  10 ,  FIG. 1E  depicts a diagram of a voltage standing wave radio (VSWR) of the broadband antenna  10 , and  FIG. 1F  depicts a diagram of a radiation efficiency of the broadband antenna  10 . The broadband antenna  10  may be used in a wireless communication device for transmitting and receiving wireless signals of multiple different frequency bands such as the LTE/GSM850/GSM900 band (ranging from 791 MHz to 960 MHz) and the GSM1800/GSM1900/UMTS/LTE2300/LTE2500 band (ranging from 1710 MHz to 2700 MHz). The broadband antenna  10  includes a substrate  100 , a radiating part  102 , a signal feed-in element  104 , a grounding unit  106 , a shorting unit  108 , a feed-in point FP 1 , a capacitor C 1  and an inductor L 1 . The substrate  100  is a double-sided substrate. The radiating part  102  is disposed on the first plane (e.g. the front side) of the substrate  100  and the shorting unit  108  is disposed on the second plane (e.g. the back side) of the substrate  100 . The grounding unit  106  may be two metal sheets connecting to each other, and the two metal sheets may be disposed on the first plane and the second plane of the substrate  100 , respectively. The feed-in point FP 1  is located on the radiating part  102 . Radio signals are transmitted from the signal feed-in element  104  to the radiating part  102  mainly through the feed-in point FP 1 , and are then emitted to the air. A grounding terminal of the signal feed-in element  104  may be connected with a system grounding unit of the wireless communication device or a grounding terminal of a coaxial cable. The capacitor C 1  is electrically connected between the feed-in point FP 1  and the signal feed-in element  104 . The inductor L 1  is electrically connected between the capacitor C 1  and the grounding unit  106  (i.e., a terminal of the inductor L 1  is electrically connected to the capacitor C 1 , and another terminal of the inductor L 1  is electrically connected to the grounding unit  106 ). With the passive elements such as the capacitor C 1  and the inductor L 1 , the broadband antenna  10  has more modes of resonance than an antenna without passive elements, and therefore improves the antenna bandwidth and reduces the antenna dimension. 
     In detail, a terminal of the shorting unit  108  is electrically connected to the radiating part  102 , and another terminal of the shorting unit  108  is electrically connected to the grounding unit  106 . The radiating part  102  may include a first radiating element  1020  and a second radiating element  1022  on the first plane of the substrate  100 , and include a third radiating element  1024  and a fourth radiating element  1026  on the second plane of the substrate  100 . The substrate  100  may have one or more vias, which may be located in the area where the radiating part  102  is disposed, for electrically connecting the first radiating element  1020  with the third radiating element  1024  and electrically connecting the second radiating element  1022  with the fourth radiating element  1026 . In another embodiment, the one or more vias may be located in the area where the grounding unit  106  is disposed so as to connect with each other the two metal sheets of the grounding unit  106  disposed on the first and the second planes of the substrate  100 . As shown in  FIG. 1C , the shorting unit  108  may electrically connect the third radiating element  1024  and the fourth radiating element  1026  with the part of the grounding unit  106  disposed on the second plane of the substrate  100 . The shorting unit  108 , the third radiating element  1024 , the fourth radiating element  1026 , and the part of the grounding unit  106  disposed on the second plane of the substrate  100  are formed by a single, continuous metal sheet. The shorting unit  108  is formed to extend substantially toward the direction D 2 . The first radiating element  1020  and the third radiating element  1024  also extend substantially toward the direction D 2 . The third radiating element  1024  substantially overlaps a projected area which is resulted from projecting the first radiating element  1020  onto the second plane of the substrate  100 , and the fourth radiating element  1026  substantially overlaps another projected area which is resulted from projecting the second radiating element  1022  onto the second plane of the substrate  100 . The connecting parts  112 ,  114  and  116  are located around the two terminals of the capacitor C 1  and the inductor L 1  on the substrate  100  such that the capacitor C 1  can be electrically connected between the feed-in point FP 1  and the signal feed-in element  104  and the inductor L 1  can be electrically connected between the capacitor C 1  and the grounding unit  106 . The connecting parts  112 ,  114  and  116  may be metal connecting sheets or solder joints which solder the capacitor C 1  and the inductor L 1  on the substrate  100 . 
     Since the capacitor C 1  is electrically connected between the feed-in point FP 1  and the signal feed-in element  104 , radio signals from the signal feed-in element  104  are largely transmitted to the feed-in point FP 1  via the capacitor C 1 . The current then flows to the radiating part  102  for emitting the radio signals. In the X-Y plane, the third radiating element  1024  partially overlaps the first radiating element  1020 , and the fourth radiating element  1026  partially overlaps the second radiating element  1022 . Therefore, radio signals in the radiating elements  1020  and  1022  are coupled to the radiating elements  1024  and  1026 . Owing to the coupling effect, the current on the third radiating element  1024  is induced by the current on the first radiating element  1020 , and these currents have the same direction. Similarly, the current on the fourth radiating element  1026  is induced by the current on the second radiating element  1022 , and these currents have the same direction. As a result, the effective area of the radiating part  102  is increased. Thus, the antenna dimension of the broadband antenna  10  can be reduced while broadband impedance matching is achieved. 
       FIG. 1D  illustrates a vertical section of the broadband antenna  10  which is viewed from the left to the right of the broadband antenna  10  shown in  FIG. 1A .  FIG. 1D  shows that the broadband antenna  10  may further include a metal plate  118  electrically connected to the radiating part  102 . The metal plate  118  may be substantially vertical to the plane defined by the radiating part  102 , but is not limited herein. The intersection of the metal plate  118  and the radiating part  102  may form any angle smaller than 180 degrees. The metal plate  118  is regarded as an extension of the radiating part  102  along Z-axis, which also radiates electromagnetic waves and therefore increases the effective area of the antenna. 
     In an embodiment, an electrical length of the first radiating element  1020  is larger than an electrical length of the second radiating element  1022 . The first radiating element  1020  and the second radiating element  1022  are connected to each other and are shorted to the grounding unit  106  for resonating at a low frequency band and a high frequency band, respectively. The capacitor C 1 , together with the first radiating element  1020  and the second radiating element  1022 , is used to induce a resonance mode at another high frequency band. In all, the broadband antenna  10  can resonate at least three frequency bands. Moreover, the inductor L 1  is used to improve impedance matching of the low frequency band. In some embodiments, an effective capacitance of the capacitor C 1  is substantially between 1 pF to 20 pF, and an effective inductance of the inductor L 1  is substantially between 1 nH and 20 nH. The signal feed-in element  104  is used to connect to a signal line of a wireless communication system for transmitting radio signals. In order to obtain better radiation pattern, the feed-in direction D 1  of the signal feed-in element  104  is substantially parallel to the resonance directions D 2  and D 3  on the radiating part  102 . With appropriate selection for the dimensions of the radiating part  102  and the shorting unit  108  and the values of the capacitor C 1  and the inductor L 1 , the broadband antenna  10  may be designed to comply with wireless communication systems having different operational frequency bands, such as the Long-Term Evolution (LTE) and the Global System for Mobile Communications (GSM). As shown in  FIG. 1E , the broadband antenna  10  has broad bandwidth and preferable impedance matching. In addition, the radiation efficiency of the broadband antenna  10  is maintained at around 50% in the operational frequency bands (791 MHz-960 MHz and 1710 MHz-2700 MHz) as shown in  FIG. 1F . 
     Noticeably, the present invention disposes passive elements such as capacitors and inductors in the proximity of the signal feed-in element of the antenna, thereby improving the antenna bandwidth and impedance matching. Those skilled in the art may make modifications and/or alterations accordingly. For example, the substrate  100  may be a printed circuit board, and the components of the broadband antenna  10  shown in  FIG. 1A  may be printed on the substrate  100 . In another example, components such as the first radiating element  1020 , the second radiating element  1022 , the third radiating element  1024 , the fourth radiating element  1026 , the grounding unit  106  and the shorting unit  108  may be implemented by metal plates. In addition, the radiating part  102  and the grounding unit  106  disposed on the first and the second planes of the substrate  100  may be electrically connected by using one or more vias or metal wires. The broadband antenna  10  shown in  FIG. 1A  is an inverted-F antenna, but is not limited herein. The concept of utilizing passive elements such as capacitors and inductors for improving antenna bandwidth and impedance matching maybe applied to various antenna structures, e.g., monopole antenna, dipole antenna, folded dipole antenna or slot antenna. 
     Please refer to  FIG. 2 , which is a schematic diagram of a broadband antenna  20  according to an embodiment of the present invention. Comparing  FIG. 2  with  FIG. 1A , the radiating elements of the broadband antenna  20  and the broadband antenna  10  are similar in shape, but the broadband antenna  20  includes one more inductors L 2 . The radiating part  202  includes a first radiating element  2020 , a second radiating element  2022  and a fifth radiating element  2028 . The radiating part  202  has a break in between the first radiating element  2020  and the fifth radiating element  2028  (i.e. a branch of the radiating part  202  is separated into two radiating elements  2020  and  2028  by the break). The inductor L 2  is disposed across the break, and is electrically connected between the first radiating element  2020  and the fifth radiating element  2028 . By adding the inductor L 2  to the radiating part  202 , the broadband antenna  20  may resonate at an additional high frequency band, and therefore further increases the antenna bandwidth. 
     Please refer to  FIG. 3A  to  FIG. 3C .  FIG. 3A  is a schematic diagram of a broadband antenna  30  according to an embodiment of the present invention,  FIG. 3B  illustrates a plane of the broadband antenna  30 , and  FIG. 1C  illustrates another plane of the broadband antenna  30 . Comparing  FIG. 3A to 3C  with  FIG. 1A to 1C , the radiating elements of the broadband antenna  30  and the broadband antenna  10  are similar in shape, but the shorting unit  308  and the second radiating element  3022  extend toward the same direction D 3  whereas the shorting unit  108  and the second radiating element  1022  extend toward the opposite directions. In other words, a horizontal projection result of the second radiating element  3022  (i.e. a result of projecting the second radiating element  3022  to the X-axis) substantially overlaps a horizontal projection result of the shorting unit  308  (i.e. a result of projecting the shorting unit  308  to the X-axis). Since the direction to which the shorting unit  308  extends is changed from the direction D 2  to the direction D 3 , another resonance mode may be induced in the broadband antenna  30 . As a result, the broadband antenna  30  may have another operational frequency band which complies with the frequency requirement of another wireless communication system. 
     Please refer to  FIG. 4 , which is a schematic diagram of a broadband antenna  40  according to an embodiment of the present invention. Comparing  FIG. 4  with  FIG. 1A , the radiating elements of the broadband antenna  40  and the broadband antenna  10  are similar in shape, but in the broadband antenna  10  the radiating part  102  and the shorting unit  108  are disposed on different planes of the substrate  100 , whereas in the broadband antenna  40  the radiating part  402  and the shorting unit  408  are disposed on the same plane of the substrate  400 . Moreover, in the broadband antenna  10 , the conjunction part of the first radiating element  1020  and the second radiating element  1022  extends toward the grounding unit  106 , and its shape is an inequilaterally inverted triangle. On the other hand, in the broadband antenna  40 , the conjunction part of the first radiating element  4020  and the second radiating element  4022  extends toward the grounding unit  406 , and its shape is an inverted right triangle. The shape of the conjunction part of the first radiating element and the second radiating element is not limited herein. In other examples, the shape of the conjunction part may be an inequilaterally inverted triangle or an equilaterally inverted triangle. Alternatively, the shape of the conjunction part may be rectangular, wedge-shaped, triangular, trapezoid, or any geometric shapes combined. The conjunction part may be properly modified according to antenna design requirements in order to adjust the impedance matching of the antenna. 
     In the aforementioned embodiments, the broadband antennas  10 ,  20 ,  30  and  40  are realized in a form of direct feed antenna structure. Radio signals are fed to the first radiating elements  1020 ,  2020 ,  3020 ,  4020  and the second radiating elements  1022 ,  2022 ,  3022 ,  4022  through the feed-in points FP 1 , FP 2 , FP 3 , or FP 4 . In other embodiments, the broadband antenna of the present invention may be realized in a form of coupling feed antenna structure. 
     Please refer to  FIG. 5 , which is a schematic diagram of a broadband antenna  50  according to an embodiment of the present invention. The broadband antenna  50  includes a substrate  500 , a radiating part  502 , a signal feed-in element  504 , a grounding unit  506 , a coupling excitation unit  508 , a feed-in point FP 5 , a capacitor C 1  and an inductor L 1 . The radiating part  502  includes a low-frequency radiating element  5020  and a high-frequency radiating element  5022 . The feed-in point FP 5  is located on the high-frequency radiating element  5022 . The low-frequency radiating element  5020  keeps a distance d 1  from the high-frequency radiating element  5022  such that radio signals feed in the low-frequency radiating element  5020  from the high-frequency radiating element  5022  by coupling effect. The coupling excitation unit  508  is electrically connected between the low-frequency radiating element  5022  and the grounding unit  506 . The coupling excitation unit  508  also keeps a distance d 2  from the high-frequency radiating element  5022  so as to enhance the coupling effect between the low-frequency radiating element  5020  and the high-frequency radiating element  5022 , which therefore induces different resonance modes. The distances d 1  and d 2  may be properly adjusted according to the area, shape, location and impedance matching requirements of the low-frequency radiating element  5020 , the high-frequency radiating element  5022 , and the coupling excitation unit  508 . In other words, the distances d 1  and d 2  do not have to be constant values. A horizontal projection result of the low-frequency radiating element  5020  (i.e. a result of projecting the low-frequency radiating element  5020  to the X-axis) substantially overlaps a horizontal projection result of the high-frequency radiating element  5022  (i.e. a result of projecting the high-frequency radiating element  5022  to the X-axis). In consideration of the limited antenna disposition area and the requirement for better coupling effect and radiation efficiency, the high-frequency radiating element  5022  may be a metal sheet or plate with non-uniform width. 
     In addition, the antenna radiation frequency, bandwidth and efficiency are closely correlated with the antenna shape and the materials used in the antenna. Therefore, designers may appropriately modify the broadband antennas  10 ,  20 ,  30 ,  40  and  50  to comply with requirements of the wireless communication systems. Note that the examples and embodiments mentioned above are used to illustrate the concept of the present invention, which utilizes passive elements such as capacitors and inductors disposed in the proximity of the signal feed-in element of the antenna for improving the antenna bandwidth and impedance matching. Any alterations and modifications such as varying the material, shape, location of the components should be within the scope of the present invention as long as the concept of the present invention is met. 
     Please refer to  FIG. 6 , which a schematic diagram of a wireless communication device  60  equipped with the broadband antenna  40  shown in  FIG. 1A . The wireless communication device  60  maybe any electronic device having wireless communication functionality such as a cell phone, a tablet PC, a laptop, an electronic reading device, a computer system, and a wireless access point.  FIG. 6  simply depicts that the wireless communication device  60  may include a shell  600 , the broadband antenna  10  and a radio signal processing unit. The broadband antenna  10  is disposed inside the shell  600 , and is used for transmitting and receiving wireless signals in multiple frequency bands so as to allow the wireless communication device  60  to support wireless communication protocols having different operational frequency bands. As such, the wireless communication device  60  can be compatible with different communication specifications regulated in different countries. 
     In conclusion, the present invention utilizes passive elements such as capacitors and inductors disposed in the proximity of the signal feed-in element of the antenna to induce multiple resonance modes and achieve preferable impedance matching. In this way, the antenna of the present invention can have broader bandwidth and smaller size than its counterparts without passive elements. 
     Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.