Patent Publication Number: US-9425510-B2

Title: Coupled dual-band dipole antenna with interference cancellation gap, method of manufacture and kits therefor

Description:
CROSS-REFERENCE 
     This application claims the benefit of PCT Application No. PCT/US2011/61625 filed Nov. 11, 2011, which claims the benefit of U.S. Provisional Application No. 61/416,365, filed Nov. 23, 2010, which applications are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates in general to an antenna and, in particular, to a planar antenna. More particularly, the present invention relates to a coupled dual-band dipole antenna having an interference-cancellation gap for wireless applications such as Wi-Fi™, wireless HDTV, Bluetooth, Public Safety, RFID, WIMAX, tolling, remote control and unlicensed band wireless applications. The invention is suitable for use in any wireless application which uses 2400-2500 MHz and 4900-6000 MHz bands. 
     2. Background of the Invention 
     In recent years there has been a tremendous increase in the use of wireless devices. The increased use has filled all or nearly all existing frequency bands. As a result, new wireless frequency standards continue to emerge throughout the world. 
     Based on the IEEE 802.11 standards, Wi-Fi™ has become the de facto standard for wireless local area network (WLAN) devices, which includes cell phones, smart phones and PDA devices, and laptop and desktop personal computers. Extensive efforts have been devoted to the development of an antenna that can be used to cover the entire frequency range of the latest Wi-Fi™ standard to keep overall device costs down. 
     For the latest dual-band Wi-Fi antennas, increased interference is problematic in the 2.4 and 5 GHz frequency modes. It has also been difficult for a single antenna to be optimized for both frequency modes. Currently antennas are either optimized for one frequency or another or performance in both modes results in poor efficiency. Previously disclosed planar antennas include, for example, those disclosed in U.S. Pat. No. 6,917,339 B2 to Li et al. for Multi-Band Broadband Planar Antennas; U.S. Pat. No. 6,346,914 B1 to Annamaa for Planar Antenna Structure 
     SUMMARY OF THE INVENTION 
     An aspect of the disclosure is directed to planar antennas. Planar antennas typically comprise: a substrate; a conductive layer attached to a first surface of the substrate wherein the conductive layer further comprises an antenna section which includes a ground section having an upper, shorter and generally horizontal section and a lower, longer generally horizontal section connected at one end by a vertical segment, and a radiation section having a substantially mirror image shape as the ground section. Each of the antenna section and the ground section can be formed from a layer of patterned foil adhered to the first surface of the substrate. As shown, the antenna section and the ground section have a combined overall width of from about 30 mm to 58 mm and a height of from about 3 mm to about 15 mm, and more preferably the antenna section and the ground section have a combined overall width of from about 42 mm and a height of about 7 mm. Additionally, the antenna section and the ground section adhered to the substrate typically have a combined overall thickness of from about 0.05 min to about 0.15 mm, and even more preferably a combined overall thickness of about 0.1 mm. The radiation element further comprises a first horizontally longer section at a first end and a parallel shorter section below the first horizontally longer section, wherein the second section is proximal the ground element. The substrate typically is at least one of a Flame Retardant 4 material, a flexible printed circuit substrate, and a single-side printed circuit board substrate. Moreover, the conductive layer is typically selected from the group comprising copper, aluminum, nickel, silver, and chrome. An insulation layer may also be provided on top of the conductive layer. The insulation layer can be configured such that it has an aperture defining a ground access point exposing a portion of the ground element. Additionally, the insulation layer can be configured to provide an aperture defining a feed point exposing a portion of the radiation element. The dual band operation of the antenna includes, for example, a first frequency from 2400-2500 MHz and a second frequency from 4900-6000 MHz. 
     Another aspect of the disclosure is directed to planar antennas manufactured by patterning a substrate comprising a dielectric layer, and a conductive layer applied to at least one surface of the substrate. Planar antennas manufactured by patterning a substrate comprise: a conductive layer attached to a first surface of the substrate wherein the conductive layer further comprises an antenna section which includes a ground section having an upper, shorter and generally horizontal section and a lower, longer generally horizontal section connected at one end by a vertical segment, and a radiation section having a substantially mirror image shape as the ground section, wherein the substrate has a substantially rectangular shape. Each of the antenna section and the ground section can be formed from a layer of patterned foil adhered to the first surface of the substrate. As shown, the antenna section and the ground section have a combined overall width of from about 30 mm to 58 mm and a height of from about 3 mm to about 15 mm, and more preferably the antenna section and the ground section have a combined overall width of from about 42 mm and a height of about 7 mm. Additionally, the antenna section and the ground section adhered to the substrate typically have a combined overall thickness of from about 0.05 mm to about 0.15 mm, and even more preferably a combined overall thickness of about 0.1 mm. The radiation element further comprises a first horizontally longer section at a first end and a parallel shorter section below the first horizontally longer section, wherein the second section is proximal the ground element. The substrate typically is at least one of a Flame Retardant 4 material, a flexible printed circuit substrate, and a single-side printed circuit board substrate. Moreover, the conductive layer is typically selected from the group comprising copper, aluminum, nickel, silver, and chrome. An insulation layer may also be provided on top of the conductive layer. The insulation layer can be configured such that it has an aperture defining a ground access point exposing a portion of the ground element. Additionally, the insulation layer can be configured to provide an aperture defining a feed point exposing a portion of the radiation element. The dual band operation of the antenna includes, for example, a first frequency from 2400-2500 MHz and a second frequency from 4900-6000 MHz. 
     Still another aspect of the disclosure is directed to an antenna kits which include one or more antennas. Antenna kits comprise: a planar antenna comprising a substrate a conductive layer attached to a first surface of the substrate wherein the conductive layer further comprises an antenna section which includes a ground section having an upper, shorter and generally horizontal section and a lower, longer generally horizontal section connected at one end by a vertical segment, and a radiation section having a substantially mirror image shape as the ground section. Additionally, the kits can include other components such as a flexible cable adaptable to connect the planar antenna to a target device, and a planar antenna mounting material. 
     INCORPORATION BY REFERENCE 
     All publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The novel features of the invention are set forth with particularity in the appended claims. A better understanding of the features and advantages of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the invention are utilized, and the accompanying drawings of which: 
         FIGS. 1 a - e    illustrate a planar antenna in accordance with the disclosure;  FIG. 1 a    illustrates a top planar view of the antenna;  FIG. 1 b    illustrates a cross-sectional side view along the lines  1   b - 1   b  of  FIG. 1 a   ;  FIG. 1 c    illustrates a cross-sectional side view along the lines  1   c - 1   c  of  FIG. 1 a   ;  FIG. 1 d    illustrates a cross-sectional side view along the lines  1   d - 1   d  of  FIG. 1 a   ;  FIG. 1 e    illustrates an expanded view of the substrate and antenna layers; 
         FIG. 2  shows the simulation result of current distribution for the antenna of  FIGS. 1 a - e    working in the 2.4 GHz Wi-Fi mode; 
         FIG. 3  shows the simulation result of current distribution for the antenna of  FIGS. 1 a - e    working in the 5 GHz Wi-Fi mode; 
         FIG. 4  illustrates an antenna segment responsible for characteristic adjustments of the antenna of  FIGS. 1 a   - e;    
         FIG. 5  shows the gain characteristic of the antenna of  FIGS. 1 a - e    working under the 2.4 GHz Wi-Fi mode; and 
         FIG. 6  shows the gain characteristic of the antenna of  FIGS. 1 a - e    working under the 5 GHz Wi-Fi mode. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The disclosure provides a coupled dual-band dipole antenna that has cancelled electromagnetic interference suitable for use in any wireless application which uses 2400-2500 MHz and 4900-6000 MHz bands. Wireless applications include, for example, Wi-Fi™, wireless HDTV, Bluetooth, Public Safety, RFID, tolling, remote control and unlicensed band wireless applications. 
     Wi-Fi™ is a trademark of the Wi-Fi Alliance and typically refers only to a narrow range of connectivity technologies including wireless local area networks (WLAN) based on the IEEE 802.11 standards, device-to-device connectivity (such as Wi-Fi peer-to-peer), and a range of technologies that support personal area networks (PAN), local area networks (LAN) and WAN connections. Wi-Fi has become a superset of IEEE 802.11. 
     As will be appreciated by those skilled in the art, the disclosure herein enables a coupled dual-band dipole antenna with interference cancelling. The antenna is adapted and configured to cancel electromagnetic interference. Thus, antennas can operate in a dual-band mode while being simultaneously optimized to efficiently perform in two modes during operation. A planar dipole antenna is disclosed that provides for dual-band wireless application which operate in the 2400-2500 MHz and 4900-6000 MHz bands. The antennas comprise a ground section and a radiation section. The ground section can be adhered to a substrate and is shaped to have an upper, shorter and generally horizontal segment and a lower, longer and also generally horizontal segment that are connected at one end by a vertical segment. The radiation section is adhered to the substrate and has an approximate shape that is substantially a mirror image about the z axis of the ground section and is spaced from the ground section by a gap at the end of the ground section and radiation section where the shorter and longer horizontal segments thereof are connected 
     I. Antennas 
       FIG. 1 a    illustrates a top view of a planar antenna. The antenna  100  has a planar antenna. As is illustrated, the antenna  100  has a ground element section  144  and an antenna section  142 . Each of these sections with its electrically conductive layer of a correspondingly specific shaping is, typically, a layer of copper foil adhered to the surface of a suitable substrate  110 . 
     The ground element  124  of the ground section  144  can further be masked by a protective layer  150  leaving only a ground access point  134  exposed. Similarly, the radiation element  122  of the antenna section  142  can be adapted and configured to provide an unmasked feed point  132 . The ground access point  134  and feed point  132  can provide a location for the antenna to achieve an electrical connection to the antenna circuitry of the electronic equipment relying on the antenna for electromagnetic signal transmission and reception. The radiation element  122  is adhered to the substrate  110  and has an approximate shape that is substantially a mirror image about the z axis, essentially bisecting the length of the antenna, of the ground element  124  and is spaced from the ground section  144  by a gap at the end of the ground section  144  and radiation section  142  where the shorter horizontal section  156 ,  156 ′ forming a perpendicular arm between two parallel sections of the ground section  144  and the antenna section  142  and the longer horizontal segment  154 ,  154 ′ are connected by corresponding vertical section  158 ,  158 ′. The ground element  144  is formed in a plane and has a first section in the shape of a truncated arrowhead, wherein the arrowhead portion is cut in half along its long axis, and a second section having a tapered rectangular shape forming a partial right triangle. The two sections of the ground element  144  are connected by a perpendicular arm section or vertical section  158  which connects the two sections at one end. The antenna section  142  has a first section in the shape of a truncated arrowhead, wherein the arrowhead portion is cut in half along its long axis, and a second section having a tapered rectangular shape forming a partial right triangle. The two sections of the antenna section  142  are connected by a perpendicular arm section or vertical section  158 ′ which connects the two sections at one end. The vertical section  158  of the ground element  144  is adjacent the vertical section  158 ′ of the antenna section  142 . 
     Turning now to  FIGS. 1 b - d   , a substrate  110  is provided upon which the antenna element sits. A top insulation layer  150  can also be provided to electrically isolate, or selectively electrically isolate, the antenna element from the surrounding area. As shown in  FIG. 1 b   , which is a cross-section of the antenna taken along the lines  1   b - 1   b  of  FIG. 1 a   , the longer horizontal segments  154 ,  154 ′ of the radiation element  122  and ground element  124  of the antenna sit atop the substrate  110  and are covered by an insulation layer  150 . As ground access point  134  is exposed on the ground element  124 . As can be seen in the cross-section shown in  FIG. 1 c   , which is a cross-section of the antenna taken along the lines  1   c - 1   c  of  FIG. 1 a   , the entire surface of the substrate  110  is covered by the insulation layer  150  and ground access point  134  is exposed over a narrower section along the vertical section  158  of the ground element  124  while radiation element  122  along the vertical section  158 ′ is not exposed. Turning now to the cross-section shown in  FIG. 1 d   , an opening in the insulation layer  150  is provided which provides a feed point  132  to the radiation element  122  and the shorter horizontal sections  156 ,  156 ′ of the ground element  124  and the radiation element  122  are covered by insulation. The overall thickness T 1  of the antenna ranges from 0.05 mm to 0.15 mm and more preferably about 0.1 mm. 
     Turning now to  FIG. 1 e   , the ground element  124  and radiation element  122  of suitable material, such as copper, is sized to be positioned on a substrate  110 . The overall dimensions of the combined ground element  124  and radiation element  122  is L 1  along one axis and W 1  along a second access, where L 1  typically ranges from 30 mm to 58 mm, more preferably from 40 mm to 45 mm, and even more preferably about 42 mm, and W 1  typically ranges from 3 mm to 15 mm, more preferably from 5 mm to 9 mm, and even more preferably about 7 mm. The overall dimensions of the antenna is generally rectangular. 
       FIG. 2  shows the simulation result of current distribution for an antenna constructed according to  FIGS. 1 a - e    wherein the antenna is operating in a 2.4 GHz Wi-Fi mode.  FIG. 3  shows the simulation result of current distribution for an antenna of  FIGS. 1 a - e    operating in a 5 GHz Wi-Fi mode. Inductive circles  310 ,  310 ′ show in  FIG. 3  illustrate the greatest current that is closely related to antenna impedance matching. 
       FIG. 4  illustrates the antenna segments responsible for characteristics adjustment of the antenna of  FIGS. 1 a - e   . According to the present invention, physical dimensions of several radiation control sections of the antenna copper patterning can be used as control factors for performance adjustment of antenna  100 . For example, radiation control sections generally indicated by phantom-lines  162 ,  164 ,  166 . The ground element  124  has a distance  169  between the adjacent the vertical section  158  of the short and long horizontal segments of the ground element  124 , as well as spacing  168  between the radiating element  122  and the ground element  124  which can be used as control factors for the performance adjustment of antenna  100 . Performance characteristics include, for example, the operating frequency bandwidth, the antenna electrical characteristics, and operating efficiency. These characteristics can be tweaked for the 2.4 and 5 GHz bands of the antenna  100  applications. 
     In one example, dimensioning of the radiation control section  162 , a horizontal copper section from which the main copper of the upper segment of the radiating element  122  extends away from a symmetric centre of the antenna  100 , can be altered to facilitate the antenna impedance matching for the 5 GHz mode of operation. 
     In another example, width of the radiation control section  164 , which is substantially the radiating element of the antenna, affects the distribution of the antenna bandwidth that is targeted at 4.5˜6.5 GHz. 
     Moreover, the width of the radiation control section  166 , substantially the entire lower segment of the radiating element  122  of the antenna  100 , can be altered to facilitate the settlement of the antenna center frequency as well as the bandwidth in the 2 GHz mode of operation. 
     The width of the radiation control section  168 , which is a distance, or gap, between the radiating element  122  and the ground element  124  of the antenna, governs the antenna efficiency. In principle, the smaller the width of section  168  the better the antenna performs. Increased performance features result from of the effect of electromagnetic (EM) wave cancellation due to the presence of this gap. Such EM cancellation reduces antenna transmission loss. In a preferred embodiment of the present invention, the width of the this radiation control section  168  (the gap between the two radiating segments of the antenna) is about 0.6 mm. 
     Meanwhile, length of the radiation control section  169 , the distance between the upper segment  156  and lower segment  158  of either the radiating element  122  or the ground element  124  of the antenna  100 , is a factor to control the mutual interference between the 2 GHz and the 5 GHz bands of the antenna. It also affects the antenna overall bandwidth as well as efficiency. In general, the smaller this length (or, the closer together the two horizontal segments of the antenna copper) the lower the antenna efficiency. 
     II. Operation and Use of the Antennas 
     The antenna can be provided with a flexible cable adapted and configured to connect the antenna to the electronics of the target device, such as a mobile phone. Alternatively, the antenna can be configured such that no cable is required to connect the antenna to the target device. For a cable-less antenna, pads are provided on the antenna which provide connections from a module or transmission line via metal contacts or reflow solder. 
     The antenna can be affixed to a housing of a target device, such as an interior surface of a cell phone housing. Affixing the antenna can be achieved by using suitable double sided adhesive, such as 3M™ Adhesive Transfer Tape 467 MP available from 3M. 
     As will be appreciated by those skilled in the art, the larger the antenna surface area (or volume), in general the higher the performance in terms of gain and radiation characteristics. Additionally, the gain of the antenna is closely linked to the surface area or volume of the antenna. Thus, the larger the surface area or volume, the higher the gain. In deploying the antenna, clearances can be provided to optimize performance of the antenna. As will be appreciated by those skilled in the art, the larger the clearance, the better the radiation characteristics of the antenna. 
     III. Method of Manufacturing the Antennas 
     The features and functions of the antennas described herein allow for their use in many different manufacturing configurations. For example, in a wireless communication handheld device (e.g. a mobile phone), an antenna can be printed on any suitable substrate including, for example, printed circuit boards (PCB) or flexible printed circuits (FPC). The PCB or FPC is then used to mechanically support and electrically connect the antenna to the electronics of the device deploying the antenna using conductive pathways. tracks or signal traces etched from copper sheets, for example, that has been laminated onto a non-conductive substrate. The printed piece can then be mounted either at the top of the handset backside or at the bottom of the front side of the handset. Thus, antennas  100  according to this disclosure can be manufactured, for example, using a standard low-cost technique for the fabrication of a single-side printed circuit board. Other manufacturing techniques may be used without departing from the scope of the disclosure. 
     Techniques for manufacturing antennas include determining which materials, processes will be followed. For example, a printed circuit board (PCB), an electrically thin dielectric substrate (e.g., RT/diroid 5880), Flame Retardant 4 (FR-4) material complying with the UL-94-V0, or any suitable non-conductive board can be used as the substrate. A conductive layer is provided from which the antenna will be formed. The conductive layer is generally copper, but other materials can be used without departing from the scope of the disclosure. For example, aluminum, chrome, and other metals or metal alloys can be used. 
     Data for identifying a configuration for the antenna layer is provided which can then be placed onto an etch resistant film that is placed on the conductive layer which will form the antenna. A traditional process of exposing the conductive layer, and any other areas unprotected by the etch resistant film, to a chemical that removes the unprotected conductive layer, leaving the protected conductive layer in place. As will be appreciated by those skilled in the art, newer processes that use plasma/laser etching instead of chemicals to remove the conductive material, thereby allowing finer line definitions, can be used without departing from the scope of the disclosure. 
     Multilayer pressing can also be employed which is a process of aligning the conductive material and insulating dielectric material and pressing them under heat to activate an adhesive in the dielectric material to form a solid board material. In some instances, holes can be drilled for plated through applications and a second drilling process can be used for holes that are not to be plated through. 
     Plating, such as copper plating, can be applied to pads, traces, and drilled through holes that are to be plated through. The antenna boards can then be placed in an electrically charged bath of copper. A second drilling can be performed if required. A protective masking material can then be applied over all or select portions of the bare conductive material. The insulation protects against environmental damage, provides insulation, and protects against shorts. Coating can also be applied, if desired. As a final step, the markings for antenna designations and outlines can be silk-screened onto the antenna. Where multiple antennas are manufactured from a panel of identical antennas, the antennas can be separated by routing. This routing process also allows cutting notches or slots into the antenna if required. 
     As will be appreciated by those skilled in the art, a quality control process is typically performed at the end of the process which includes, for example, a visual inspection of the antennas. Additionally, the process can include the process of inspecting wall by cross-sectioning or other methods. The antennas can also be checked for continuity or shorted connections by, for example, applying a voltage between various points on the antenna and determining if a current flow occurs. The correct impedance of the antennas at each frequency point can be checked by connecting to a network analyzer. 
     IV. Kits 
     The antennas disclosed herein can be made available as part of a kit. The kit comprises, for example, a planar antenna comprising a substrate a conductive layer attached to a first surface of the substrate wherein the conductive layer further comprises an antenna section which includes a ground section having an upper, shorter and generally horizontal section and a lower, longer generally horizontal section connected at one end by a vertical segment, and a radiation section having a substantially mirror image shape as the ground section. Additionally, the kit may include, for example, suitable mounting material, such as 3M adhesive transfer tape. Other components can be provided in the kit as well to facilitate installation of the antenna in a target device, such as a flexible cable. The kit can be packaged in suitable packaging to allow transport. Additionally, the kit can include multiple antennas, such that antennas and cables are provided as 10 packs, 50 packs, 100 packs, and the like. 
     V. Examples 
     Experimental antennas according to this disclosure have been constructed and tested.  FIG. 5  shows an actual measured gain characteristic of an embodiment of an antenna  100  operating in the 2.4 GHz Wi-Fi mode, and  FIG. 6  shows a gain characteristic of the same antenna operating in the 5 GHz Wi-Fi mode. Antenna  100  was tested in a lab with an antenna  100  orientation as described in  FIG. 4 . TABLE 1 lists the performance specification of the antenna measured in  FIGS. 5 and 6 . 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 SPECIFICATION OF AN EXPERIMENTAL ANTENNA 
               
            
           
           
               
               
               
               
               
            
               
                 Standard 
                 Bluetooth 
                 2.4 GHz Wi-Fi 
                 5 GHz Wi-Fi 
                 Other 5 GHz 
               
               
                   
               
               
                 Band (MHz) 
                 2,401-2,480 
                 2,400-2,500 
                 5,725-5,825 
                 4,900-5,900 
               
               
                 Peak Gain 
                 3 
                 3 
                 3 
                 3 
               
               
                 (dBi) 
               
            
           
           
               
               
               
            
               
                 Average 
                 −2~−3 
                 −2~−3 
               
               
                 Gain 
               
               
                 Efficiency 
                 70-80% 
                 65-80% 
               
               
                 (%) 
               
               
                   
               
            
           
         
       
     
     As discussed above, the gain of the antenna is closely linked to the surface area or volume of the antenna. Moreover, the antenna efficiency directly relates to the actual measured radiated power and sensitivity of the wireless device it is placed into (the TRP/TIS results). The higher the efficiency, given a well matched antenna and device, the better the range and sensitivity of the device, the higher the data transfer speed, and the less power is consumed by the device. For antennas built under the designs disclosed herein, the efficiency remains high in both the 2.4 GHz and 5 GHz ranges, given the relatively small size of the antenna. 
     While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. Numerous variations, changes, and substitutions will now occur to those skilled in the art without departing from the invention. It should be understood that various alternatives to the embodiments of the invention described herein may be employed in practicing the invention. It is intended that the following claims define the scope of the invention and that methods and structures within the scope of these claims and their equivalents be covered thereby.