Patent Publication Number: US-10790583-B2

Title: Low-profile dual-band high-isolation antenna module

Description:
FIELD OF THE INVENTION 
     The present invention relates to an antenna structure and more particularly to one in which a decoupling element is disposed between two high-frequency antennas and two low-frequency antennas but not in direct contact with any of the antennas, and in which the decoupling element is designed to have the least adverse effect on the electrical performance of the antenna structure. 
     BACKGROUND OF THE INVENTION 
     The rapid development of the wireless communication industry has led to continuous improvement of wireless communication devices. In addition to lightweight and compactness, people nowadays place more and more emphasis on the communication quality of such devices, in particular the stability of signal transmission. Antennas are essential to the reception and transmission of wireless signals, or data, and hence indispensable to wireless communication devices. Research and development of antenna-related technology have been a major issue in the related technical fields, thanks also to advancements in the wireless communication industry. 
     An antenna is an electrical conductor or electrically conductive system for transmitting electromagnetic energy into, or receiving electromagnetic energy from, a space. To increase the data rates and channel capacities of antennas, “multi-input and multi-output (MIMO) systems” have been widely used, in which the antennas needed by an electronic device tend to be several times as many as in a non-MIMO system and therefore must be arranged in close proximity to one another in the limited space of the device. The mutual coupling effect of the antennas, however, may impair the isolation between, and consequently the radiation quality of, the antennas. As a solution, referring to  FIG. 1 , a neutralization line M 3  is typically connected between the two dual-band antenna radiation units M 1  and M 2  on the front side of a circuit board to provide the desired isolation in the 2.4 GHz working band, but with the neutralization line M 3  being a structure capable only of narrowband isolation, proper isolation across the entire 2.4 GHz band is unattainable. Moreover, a defected ground structure (DGS) is required to reduce the aforesaid coupling effect in the 5 GHz working band, wherein the DGS involves forming additional grooves M 4  (see  FIG. 2 ) in the grounding surface of the backside of the circuit board to provide isolation. The antenna design shown in  FIG. 1  and  FIG. 2  not only calls for a time-consuming design process, but also takes up a large area of the circuit board. In particular, the existing decoupling structures based on a neutralization line generally require the neutralization line to be integrally formed with the main bodies of the antennas to be isolated, which adds considerably to the difficulty of design. 
     According to the above, an additional decoupling mechanism is generally required for better isolation between the antennas of a dual-band MIMO antenna structure. That is to say, a manufacturer must properly adjust the space and distances between a neutralization line and the adjacent two antennas in order to provide isolation for a specific frequency band (e.g., 2 GHz or 5 GHz). This decoupling structure, however, is difficult to design in accordance with the current trend toward lightweight and compactness and occupies too much space. The issue to be addressed by the present invention is solve the aforesaid problems effectively. 
     BRIEF SUMMARY OF THE INVENTION 
     To effectively overcome the drawbacks of the decoupling mechanisms of the existing antenna structures (including the mechanisms&#39; taking up too much space), the inventor of the present invention conducted extensive research and experiment and finally succeeded in developing a low-profile dual-band high-isolation antenna module as disclosed herein. 
     One objective of the present invention is to provide a low-profile dual-band high-isolation antenna module, wherein the antenna module is fixed on a substrate and includes two high-frequency antennas, two low-frequency antennas, a decoupling element, and at least one metal strip. The two high-frequency antennas are spaced apart from each other and are located on one side of the substrate. Each of the high-frequency antennas has a bottom end configured as a feed end to be electrically connected to a feed element. The top end of each high-frequency antenna extends in a bent manner to form a high-frequency bent portion. The two low-frequency antennas are spaced apart from each other and are located on another side of the substrate. The bottom end of each low-frequency antenna is connected to a grounding of the substrate while the top end of each low-frequency antenna also extends in a bent manner to form a low-frequency bent portion. The decoupling element is disposed between the two high-frequency antennas and the two low-frequency antennas, has two ends extending to positions corresponding respectively to the low-frequency antennas, but is not in contact with the low-frequency antennas or the high-frequency antennas. The metal strip has a bottom end electrically connected to the grounding and a top end connected to the decoupling element. According to the above, the bent portions can effectively reduce the space occupied by the high-frequency antennas and the low-frequency antennas, and the fact that the decoupling element need not be connected directly to the low-frequency antennas facilitates design. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The objectives and technical features of the present invention and the intended effects of the technical features can be better understood by referring to the following detailed description in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a front view of a conventional antenna structure; 
         FIG. 2  is a rear view of the conventional antenna structure in  FIG. 1 ; 
         FIG. 3  schematically shows the antenna structure according to the first embodiment of the present invention: 
         FIG. 4  shows a test result of the antenna structure according to the first embodiment of the invention; 
         FIG. 5  shows a low-frequency-band X-Z plane radiation pattern of the antenna structure according to the first embodiment of the invention: 
         FIG. 6  shows a high-frequency-band X-Z plane radiation pattern of the antenna structure according to the first embodiment of the invention: 
         FIG. 7  schematically shows the antenna structure according to the second embodiment of the invention; and 
         FIG. 8  schematically shows the antenna structure according to the third embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 3 , the present invention provides a low-profile dual-band high-isolation antenna module composed at least of two high-frequency antennas  11  and  12 , two low-frequency antennas  21  and  22 , a decoupling element  31 , and at least one metal strip  33 . In the first embodiment of the invention, each component of the antenna module can be integrally formed of a metal plate to facilitate and speed up production; in other embodiments, each component can be assembled from a plurality of metal plates instead. For example, the decoupling element  31  in  FIG. 3  is an assembly of multiple metal plates, and so is the at least one metal strip  33 ; meanwhile, the low-frequency antenna  21  in  FIG. 3  can be integrally formed of a metal plate. This three-dimensional antenna assembly is fixed on a substrate E, whose circuits and other electronic elements are not shown in  FIG. 3  in order not to render the drawing unnecessarily complicated. A person skilled in the art can adjust the configuration of the substrate E according to product requirements without departing from the spirit of the invention, provided that the antenna module has the structures described below and can be mounted on the substrate E. 
     In the first embodiment, with continued reference to  FIG. 3 , the high-frequency antennas  11  and  12  are configured to operate in a high-frequency (such as but not limited to 5 GHz˜6 GHz) mode by receiving or transmitting electromagnetic waves of the corresponding frequency. The two high-frequency antennas  11  and  12  are located on one side (hereinafter referred to as the first side) of the substrate E and are spaced apart from each other. The bottom end of each high-frequency antenna  11 ,  12  is configured as a feed end  111 ,  112  to be electrically connected to a feed element. For example, each feed element may be a feed line that is soldered to the corresponding feed end  111  or  112  at one end. Alternatively, each feed element may be a contact pad on the substrate E, with each feed end  111 ,  112  soldered to the corresponding contact pad, and each contact pad electrically connected to a feed line. The top end of each high-frequency antenna  11 ,  12  extends in a bent manner and thus forms a high-frequency bent portion  113 ,  123 . This bent design is intended to reduce the space occupied by the high-frequency antennas  11  and  12  (i.e., to achieve the “low profile” referred to herein). In the first embodiment, each of the two high-frequency antennas  11  and  12  is T-shaped. 
     In the first embodiment, with continued reference to  FIG. 3 , the two low-frequency antennas  21  and  22  are configured to operate in a low-frequency (such as but not limited to 2.4 GHz˜2.5 GHz) mode by receiving or transmitting electromagnetic waves of the corresponding frequency. The two low-frequency antennas  21  and  22  are located on the opposite side of the substrate E and are spaced apart from each other. It should be pointed out that the high-frequency antennas  11  and  12  and the low-frequency antennas  21  and  22  in the present invention are not necessarily provided on two opposite sides of the substrate E respectively. If the substrate E is a multilayer plate structure, the high-frequency antennas  11  and  12  and the low-frequency antennas  21  and  22  can be provided elsewhere, provided that the high-frequency antennas are located in/on a different layer of the substrate E from the low-frequency antennas. Likewise, it is not required that the decoupling element  31  and the metal strips  33  be provided in/on the same layer as the high-frequency antennas  11  and  12 ; the decoupling element and the metal strips may be provided in/on a different layer from the high-frequency antennas. The bottom end of each low-frequency antenna  21 ,  22  is connected to a grounding G of the substrate E. The grounding G in  FIG. 3  is drawn in a dashed line because it is not and will not be in/on the same layer as the high-frequency antennas  11  and  12 . The size and shape of the grounding G are not limited to those shown in  FIG. 3  and can be adjusted to meet design requirements. The top end of each low-frequency antenna  21 ,  22  extends in a bent manner and thus forms a low-frequency bent portion  213 ,  223 . This bent design is intended to reduce the space taken up by the low-frequency antennas  21  and  22 . In the first embodiment, each of the two low-frequency antennas  21  and  22  is L-shaped, with the low-frequency bent portions  213  and  223  extending away from each other. In other embodiments of the invention, the low-frequency antennas may be adjusted to other shapes (e.g., T shape or U shape) according to product requirements. 
     Referring again to  FIG. 3 , the decoupling element  31  in the first embodiment is located on the first side of the substrate E (i.e., on the same side as the high-frequency antennas  11  and  12 ) and lies between the two high-frequency antennas  11  and  12 . The two ends of the decoupling element  31  extend to positions that correspond respectively to the low-frequency antennas  21  and  22 , but the decoupling element  31  is not in contact with any of the low-frequency antennas  21  and  22  and high-frequency antennas  11  and  12 . That is to say, the portion of the decoupling element  31  that is shown in  FIG. 3  as overlapping with the low-frequency antenna  21  (i.e., the portion indicated by the dashed-line circle in  FIG. 3 ) is in fact spaced apart from the low-frequency antenna  21  by the thickness, or the distance between the two opposite sides, of the substrate E. The metal strips  33  are also located on the first side of the substrate E (i.e., on the same side as the high-frequency antennas  11  and  12 ). The bottom end of each metal strip  33  is electrically connected to the grounding G. The top end of each metal strip  33  is connected to the decoupling element  31 . The metal strips  33  can be connected to the decoupling element  31  by being integrally formed therewith, by soldering, by piercing, or by other applicable techniques. 
     The antenna module in  FIG. 3  is so structured that the decoupling element  31  need not be connected directly to the low-frequency antennas  21  and  22  but is electrically connected to the grounding G through the pierced structures of the metal strips  33 . Consequently, referring to the test result shown in  FIG. 4 , the antenna module of the present invention has an isolation of −19 dB or lower when operating in a low-frequency (e.g., 2.4 GHz) band. Moreover, as connecting the decoupling element  31  electrically to the grounding G is equivalent to forming an isolating element between the two high-frequency antennas  11  and  12  to reduce the coupling effect therebetween, the antenna module of the invention has an isolation of −16 dB or lower when operating in a high-frequency (e.g., 5 GHz) band. In terms of radiation patterns, the antenna module produces a nearly omnidirectional in the X-Z plane (see  FIG. 5 ) when operating in a low-frequency (e.g., 2.4 GHz) band. Similarly, the antenna module produces a nearly omnidirectional in the X-Z plane (see  FIG. 6 ) when operating in a high-frequency (e.g., 5 GHz) band. In other words, the antenna module of the invention not only has an advantageously low profile that helps compact size (thanks to the bent portions of the high-frequency antennas  11  and  12  and of the low-frequency antennas  21  and  22 ), but also can be applied to wireless local area network (WLAN) communication products has wide coverage. 
     The decoupling element in the present invention is not directly connected to the low-frequency antennas and therefore has little impact on the lengths of current paths along the low-frequency antennas. Furthermore, the frequency band for which isolation is provided can be controlled by adjusting the size or shape or the decoupling element. For example, the decoupling element  31 A in the second embodiment as shown in  FIG. 7  has a U-shaped middle section, and the decoupling element  31 B in the third embodiment as shown in  FIG. 8  is formed as a straight line. In addition, the high-frequency antennas may be L-shaped, as demonstrated by the high-frequency antennas  11 A and  12 B in  FIG. 7 , with their respective high-frequency bent portions  113 A and  123 B extending away from each other. Last but not least, there may be a plurality of metal strips  33  as shown in  FIG. 3  or only a single metal strip  33 A as shown in  FIG. 7 . Thus, the antenna module of the invention can be modified and adjusted to meet product requirements. 
     While the invention herein disclosed has been described by means of specific embodiments, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims.