Patent Publication Number: US-9893434-B2

Title: Multi-element omni-directional antenna

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a divisional of and claims priority to commonly owned parent U.S. pending application Ser. No. 13/557,483 filed Jul. 25, 2012, the entire content of which is incorporated by reference for all purposes. 
    
    
     BACKGROUND 
     With the recent development of new technologies, such as 4G LTE, it is desirable for an antenna to cover a broad frequency bandwidth in a small physical antenna volume. If an antenna enclosure includes multiple antennas, it is also desirable to have adequate isolation between any two antennas operating in the same frequency range. 
     SUMMARY 
     In one embodiment, an antenna circuit board assembly is provided. The antenna circuit board assembly comprises a substrate having a ground plane comprised of a conductive material; a first antenna element mounted to the substrate and coupled to the ground plane; a second antenna element mounted to the substrate and coupled to the ground plane; a third antenna element mounted to the substrate and coupled to the ground plane; and a plurality of features etched into the ground plane, each of the plurality of features having a respective length and a respective width. The respective length and the respective width of each of the plurality of features are selected to increase isolation between the first, second, and third antenna elements. 
    
    
     
       DRAWINGS 
       Understanding that the drawings depict only exemplary embodiments and are not therefore to be considered limiting in scope, the exemplary embodiments will be described with additional specificity and detail through the use of the accompanying drawings, in which: 
         FIG. 1  is a side view of one embodiment of an antenna assembly. 
         FIGS. 2A and 2B  depict a front view and a side view, respectively, of an exemplary antenna element. 
         FIGS. 3A and 3B  depict a front view and a side view, respectively, of another exemplary antenna element. 
         FIGS. 4A-4D  depict views of an exemplary antenna circuit board assembly. 
         FIG. 5  is a high level block diagram of one embodiment of an exemplary communication system. 
         FIGS. 6-14  are graphs depicting exemplary measured directional patterns, as a function of both frequency and angle, of an exemplary antenna assembly. 
         FIGS. 15-17  are exemplary graphs depicting isolation between antenna elements of an exemplary antenna assembly. 
     
    
    
     In accordance with common practice, the various described features are not drawn to scale but are drawn to emphasize specific features relevant to the exemplary embodiments. 
     DETAILED DESCRIPTION 
     In the following detailed description, reference is made to the accompanying drawings that form a part hereof, and in which is shown by way of illustration specific illustrative embodiments. However, it is to be understood that other embodiments may be utilized and that logical, mechanical, and electrical changes may be made. Furthermore, the method presented in the drawing figures and the specification is not to be construed as limiting the order in which the individual steps may be performed. The following detailed description is, therefore, not to be taken in a limiting sense. 
       FIG. 1  is a side view of one embodiment of an antenna assembly  100 . The antenna assembly  100  includes a circuit board assembly  102 , a housing  107 , and a plurality of wires  110 . The circuit board assembly  102  is located inside the housing  107 , as indicated by the dashed lines. The circuit board assembly  102  includes a plurality of antenna elements  101 ,  103 , and  105  mounted to a substrate  104 , which is also referred to herein as a circuit board  104 . The circuit board  104  includes an antenna side  106  to which the antenna elements  101 ,  103 , and  105  are mounted. The circuit board  104  also includes a cable side  108  to which the wires or cables  110 , which connect to the antenna elements  101 ,  103 , and  105 , are terminated. In addition, the circuit board  104  includes a ground plane and the antenna elements  101 ,  103 , and  105  are grounded to the common ground plane of the circuit board  104 . 
     The antenna elements  101 ,  103 , and  105  are each designed to receive electromagnetic waves, and are particularly designed and/or dimensioned (e.g. sized and shaped) to operate (i.e. radiate electromagnetic waves) within one or more selected frequency ranges. The antenna elements  101  and  105  are approximately identical, in this embodiment, in terms of shape, size, and material. Antenna element  103 , on the other hand, differs from antenna elements  101  and  105  at least in terms of size and shape. Thus, in this embodiment, antenna elements  101  and  105  are configured to operate over the same frequency ranges whereas antenna element  103  is configured to operate over at least one frequency range that differs from the corresponding frequency ranges of antenna elements  101  and  105 . For example, antenna elements  101  and  105  are configured, in one embodiment, to operate over the frequency ranges 698-960 MHz and 1710-2170 MHz and antennal element  103  is configured to operate over the frequency ranges 1710-2170 MHz and 2496-2690 MHz. 
     Another example of a design characteristic of the antenna elements  101 ,  103 , and  105  is the type of material used to manufacture the antenna elements  101 ,  103 , and  105 . In an exemplary embodiment, the antenna elements  101 ,  103 , and  105  are manufactured from a metal material, such as copper or a steel material. Optionally, the material may be a cold rolled steel material. The antenna elements  101 ,  103 , and  105  may also be finished with a coating or plating, such as tin plating or another type of plating or coating that enhances electrical performance or characteristics. Additionally, the antenna elements  101 ,  103 , and  105  are selectively finished in predetermined areas of the antenna element, in some embodiments. The antenna elements  101 ,  103 , and  105  can all be manufactured from the same or different materials. 
     The antenna elements  101 ,  103 , and  105  are configured to provide hemispherical coverage in directions radially outward from the housing  107 . For example,  FIGS. 6-14  are graphs depicting exemplary measured directional patterns, as a function of both frequency and angle. In particular,  FIGS. 6-8  depict exemplary measured directional patterns in a first plane, defined by the X and Y axes, for antenna elements  101 ,  103 , and  105 , respectively.  FIGS. 9-11  depict exemplary measured directional patterns in a second plane, defined by the Y and Z axes, for antenna elements  101 ,  103 , and  105 , respectively.  FIGS. 12-14  depict exemplary measured directional patterns in a third plane, defined by the X and Z axes, for antenna elements  101 ,  103 , and  105 , respectively. 
       FIGS. 2A and 2B  depict a front view and a side view, respectively, of an exemplary antenna element  200  which can be implemented as antenna elements  101  and  105  in the antenna assembly  100  above. Antenna element  200  includes a first portion  212  having a length  217  that extends along a first plane and a second portion  214  having a length  243  that extends from the first portion  212  along a second plane that is transverse to the first plane. The first portion  212  and second portion  214  can be stamped from a stock material and formed by bending the antenna element  200  at a bend line where the first portion  212  and the second portion  214  meet. The first portion  212  and the second portion  214  each have a width  215 . In one embodiment, the length  217  is approximately 60 mm, the length  243  is approximately 10 mm, and the width  215  is approximately 65 mm. 
     When mounted on a circuit board, such as circuit board  104 , the first portion  212  extends generally perpendicularly from the circuit board and has a generally vertical orientation when the antenna assembly, e.g. antenna assembly  100 , is resting on a horizontal surface, such as a desk, a table or a floor of a building in typical applications. The second portion  214  extends generally perpendicularly from the first portion  212  such that the antenna element  200  defines an approximate right angle or orthogonal antenna element. The second portion  114  has a generally horizontal orientation when the antenna assembly is resting on a horizontal surface. 
     In this embodiment, the first portion  212  also includes a mounting section  226  having a width  229  and a height  223 , tapered sections  224  each having a height  221  and a width  227  on either side of the mounting section  226 , and flat sections  228  each having a width  235  on the outside of the tapered sections  224 . The first portion  212  has a length  219  which extends from the flat sections  228  to the top of the first portion  212  where the first portion  212  and the second portion  214  meet. The mounting section  226  is placed in contact with and bonded to a mounting pad to couple the antenna element  200  to the circuit board. 
     In addition, in the exemplary embodiment of  FIG. 2 , the first portion  212  includes a plurality of enclosed slots  216 ,  218 , and  220 . Each of the slots  216 ,  218 ,  220  is defined by a respective inner edge  316  of the first portion  212 . The respective inner edge  316  defines a perimeter of the respective slot such that the respective slot is entirely within the first portion  212 . The slots  216  and  218  each have a width  233  and a height  231 . The slot  220  has a width  237  and a height  235 . The respective width and height of the slots  216 ,  218 , and  220  are selected to control an impedance of the antenna element  200 . Additionally, the length  217  and width  215  of the first portion  212  can be selected to tune the antenna element  200  in some embodiments. It is to be understood that the characteristics of the slots  216 ,  218 , and  220  are dependent on the desired impedance of the antenna element. Hence, the size, location and number of slots can vary in other embodiments based on the desired impedance. The enclosed slots are devoid of objects therein during operation of the antenna assembly. 
     The antenna element  200  also includes an extension  222 . The extension is bent, in this example, to form an approximate right angle. The extension  222  has a length  241  that extends from the first portion  212  below the slot  220 . The extension  222  has a height  239  sufficient to contact a circuit board and is connected to the ground plane (e.g. ground plane  420  in  FIG. 4D ) via a mounting pad (e.g. mounting pad  407  in  FIG. 4A ). The width of the extension  222  is less than the width  237  of the slot  222  in this example. The length and width of extension  222  aids in controlling the impedance of the antenna element  200 . 
       FIGS. 3A and 3B  depict a front view and a side view, respectively, of another exemplary antenna element  300  which can be implemented as antenna element  103  in the antenna assembly  100  above. Unlike antenna element  200 , antenna element  300  is not bent to form first and second portions. Rather, antenna element  300  includes a single portion  302  having a width  301  and a length  303 . In one embodiment, the width  301  is approximately 32 mm and the length  303  is approximately 35 mm. When mounted on a circuit board, the length  303  extends generally perpendicularly from a circuit board and has a generally vertical orientation when the antenna assembly, e.g. antenna assembly  100 , is resting on a horizontal surface, such as a desk, a table or a floor of a building in typical applications 
     In addition, the portion  302  includes a single enclosed slot  304  in this example. The slot  304  is defined by an inner edge  318  of the portion  302 . The inner edge  318  defines a perimeter of the slot  304  such that the slot  304  is entirely within the portion  302 . The slot  304  has a width  307  and height  305 . The width  307  and height  305  are selected to control an impedance of the antenna element  300 . Additionally, the length  303  and width  301  of the portion  302  can be selected to tune the antenna element  300  in some embodiments. 
     The antenna element  300  also includes a mounting section  310  having a width  315  and a height  313 , tapered sections  308  each having a height  311  and a width  317  on either side of the mounting section  310 , and flat sections  306  each having a width  319  on the outside of the tapered sections  308 . The portion  302  has a length  325  which extends from the flat sections  306  to the top of the antenna element  302 . The mounting section  310  is placed in contact with and bonded to a mounting pad to couple the antenna element  300  to the circuit board. 
     The antenna element  300  also includes an extension  312  having a length  321  and a height  323 . The extension is bent to form an approximately right angle. The height  323  is selected such that the extension contacts and is bonded to the circuit board. The shape and size of the antenna elements  200  and  300  enable a broader frequency range in a low profile (e.g. small size) assembly than available in conventional antenna assemblies. 
     An exemplary antenna circuit board assembly  400  which includes antenna elements, such as antenna elements  200  and  300 , is shown in  FIGS. 4A-4D . In particular,  FIGS. 4A and 4B  depict top perspective views of the exemplary antenna circuit board assembly  400 .  FIG. 4C  depicts a bottom view of the exemplary antenna circuit board assembly  400 .  FIG. 4D  depicts a side view of the exemplary antenna circuit board assembly  400 . 
     The antenna circuit board assembly  400  includes a plurality of antenna elements  401 ,  403 , and  405  which correspond to antenna elements  101 ,  103 , and  105  in the exemplary antenna assembly  100  discussed above. Antenna elements  401 ,  403 , and  405  are mounted to respective mounting pads  407  on an antenna side  406  of the circuit board  404 . As shown in  FIGS. 4A-4C , the circuit board  404  has a circular shape in this embodiment. However, other shapes can be used in other embodiments. In addition, in this example, the antenna elements  401 ,  403 , and  405  are mounted along a line  409  which approximately divides the circuit board  404  in half. In particular, the antenna element  403 , which is smaller than antenna elements  401  and  405 , is located approximately in the center of the circuit board  404 . Antenna elements  401  and  405 , which are approximately identical in size and shape, are located on either side of the antenna element  403  along the line  409 . Each of antenna elements  401  and  405  are oriented such that the second portion  414  extends toward the center of the circuit board  404 . 
     In addition, the circuit board  404  includes a plurality of features  411  etched into the ground plane  420  on the cable side  408  of the circuit board  404 . The features  411  are depicted as dashed lines in  FIGS. 4A and 4B  to indicate the presence of the features  411  on the bottom or cable side  408 .  FIG. 4C  is a view of the cable side  408  which depicts the features  411  and the cable connectors  416  for each of the respective antenna elements  401 ,  403 , and  405 . Etching the features  411  removes the conductive material from the conductive ground plane  420 . For example, the ground plane  420  can be formed from a layer of copper in some embodiments. Portions of the copper are removed in predetermined patterns to form the features  411 . 
     The features  411  improve isolation between antenna elements operating in the same frequency range. For example, as noted above, in some embodiments, antenna elements  401  and  405  are configured to operate over the frequency ranges 698-960 MHz and 1710-2170 MHz, and antennal element  403  is configured to operate over the frequency ranges 1710-2170 MHz and 2496-2690 MHz. Hence, the features  411  improve isolation between the antenna elements  401 ,  403 , and  405 . 
     Each of the features  411  begins on an edge of the circuit board  404  and extends toward the center of the circuit board. The length of the features  411  is dependent on the wavelength of the operation frequency of the antenna elements. In particular, the length of the features  411  is ¼ of the corresponding wavelength. In addition, each of the features  411  is curved. The curvature of the features  411  is dependent on the selected length of the feature  411  (e.g. ¼ wavelength of the frequency) and the size of the circuit board  404 . In particular, the curvature is selected such that the etched features  411  have the desired length but do not divide the circuit board  411  in half. 
     By etching the features  411  into the ground plane  420  (e.g. removing portions of the conductive material of the ground plane), isolation of the antenna elements  401 ,  403 , and  405  is improved. Exemplary graphs depicting isolation between antenna elements  401 ,  403 , and  405  over a frequency range of 650 MHz to 3 GHz are shown in  FIGS. 15-17 . In particular,  FIG. 15  depicts isolation between antenna elements  401  and  403 .  FIG. 16  depicts isolation between antenna elements  403  and  405  and  FIG. 17  depicts isolation between antenna elements  401  and  405 . Each of  FIGS. 15-17  includes 5 reference points or markers. Table 1 below summarizes the values represented by the reference points in the respective graphs. 
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 Marker 1 
                 Marker 2 
                 Marker 3 
                 Marker 4 
                 Marker 5 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
            
               
                 FIG. 15 
                 −21.632 
                 −19.530 
                 −27.046 
                 −24.542 
                 −24.356 
               
               
                   
                 dB at 
                 dB at 
                 dB at 
                 dB at 
                 dB at 
               
               
                   
                 698 MHz 
                 920 MHz 
                 1.71 GHz 
                 2.17 GHz 
                 2.35 GHz 
               
               
                 FIG. 16 
                 −27.134 
                 −21.337 
                 −16.803 
                 −18.962 
                 −21.477 
               
               
                   
                 dB at 
                 dB at 
                 dB at 
                 dB at 
                 dB at 
               
               
                   
                 698 MHz 
                 920 MHz 
                 1.71 GHz 
                 2.17 GHz 
                 2.35 GHz 
               
               
                 FIG. 17 
                 −27.744 
                 −20.993 
                 −17.678 
                 −22.287 
                 −26.071 
               
               
                   
                 dB at 
                 dB at 
                 dB at 
                 dB at 
                 dB at 
               
               
                   
                 698 MHz 
                 920 MHz 
                 1.71 GHz 
                 2.17 GHz 
                 2.35 GHz 
               
               
                   
               
            
           
         
       
     
     It is to be understood that  FIGS. 15-17  and the values in Table 1 are provided by way of example and not by way of limitation. In particular, actual measured isolation between any two antenna elements is dependent on the specific implementation of the antenna assembly. Such variables include the operation frequency, length of the features  411 , and size of the antenna elements. 
     The features  411  depicted in  FIGS. 4A-4C  are provided for purposes of explanation. It is to be understood that characteristics of the features can be varied or modified in other embodiments. For example, the width of the features  411  can vary. Additionally, as shown in  FIGS. 4A-4C , each of the features  411 , in this embodiment, includes a first curved portion  413  and a narrower second curved portion  415  adjacent the first curved portion  413 . The length, width, and location of each of the first and second curved portions can vary in other embodiments. In addition, the number of curved portions can vary. In addition, the features  411  are depicted as continuous etchings in this example. However, it is to be understood that in other embodiments, the etched portions of each feature  411  need not be continuous and can be separated by sections of conductive material. 
       FIG. 5  is a high level block diagram of one embodiment of an exemplary communication system  500  in which an antenna assembly such as antenna assembly  100  is implemented. System  500  is a distributed antenna system (DAS). However, it is to be understood that the embodiments of the antenna assembly described herein are not limited to implementation in a remote antenna unit of a DAS and can be used in other wireless communication systems. For example, embodiments of the antenna assembly can be implemented in base stations and repeater units, and in various communication systems, such as microcell and picocell cellular networks. 
     System  500  is a field configurable distributed antenna system (DAS) that provides bidirectional transport of a portion of radio frequency (RF) spectrum between an upstream network device  501  and a plurality of remote antenna units (labeled RAU in  FIG. 5 )  506 . The network device  501  is a source of RF signals, such as a base station transceiver, wireless access point or other source of RF signals. System  500  can be implemented for use with various communication technologies including, but not limited to, a Public Switched Telephone Network (PSTN), a Global System for Mobile communications (GSM) network, a Universal Mobile Telecommunications System (UMTS) network, a Worldwide Interoperability for Microwave Access (WiMAX) network, a Wireless Broadband (WiBro) network, etc. 
     Along with network device  501  and the plurality of RAUs  506 , system  500  includes a host unit  502 , and a transport mechanism  504 . The host unit  502 , a modular host transceiver, is communicatively coupled to RAUs  506 , modular remote radio heads. Notably, although only four RAUs  506  are shown in this example, for purposes of explanation, other numbers of RAUs  506  can be used in other embodiments. For example, in some embodiments, the host unit  502  supports up to eight RAUs  506 . In addition, in some embodiments, one or more intermediary units can be optionally used between the RAUs  506  and the host unit  502 . The intermediary units (also referred to as expansion hubs) increase the number of RAUs  506  supported by the host unit  502 . For example, in one embodiment, up to eight RAUs  506  can be connected to each expansion hub and up to four expansion hubs can be coupled to the host unit  502 . 
     The host unit  502  and RAUs  506  work together to transmit and receive data to/from respective antenna assemblies  508 . In this embodiment, host unit  502  provides the interface between the network device  501  and a signal transport mechanism  504 . Each of RAUs  506  provides the interface between the signal transport mechanism  504  and a respective antenna assembly  508 . Each antenna assembly  508  is implemented using an antenna assembly such as antenna assembly  500  having a circuit board assembly such as circuit board assembly  400 . In addition, although each RAU  506  includes a single antenna assembly  508  in this embodiment, more than one antenna assembly can be associated with each RAU  506  in other embodiments. For example, more than one antenna assembly  508  can be associated with each RAU  506  for implementation of multiple-input multiple-output (MIMO) technologies such as WiMAX. 
     In this embodiment, the signal transport mechanism  504  is an optical fiber, and the host unit  502  sends optical signals through the optical fiber to the RAUs  506 . In some embodiments, a single optical fiber is used for both uplink and downlink transmissions. In other embodiments, one optical fiber is used for the uplink transmissions and another separate optical fiber is used for downlink transmission. In addition, in other embodiments, the signal transport mechanism  504  can be implemented using other media. For example, additional suitable implementations of the signal transport mechanism  504  include, but are not limited to, thin coaxial cabling or CATV cabling where multiple RF frequency bands are distributed or lower-bandwidth cabling, such as unshielded twisted-pair cabling, for example, where only a single RF frequency band is distributed. 
     During transmission, the network device  501  performs baseband processing on data and places the data onto a channel. In one embodiment, the network device  501  is an IEEE 802.16 compliant base station. Optionally, network device  501  may also meet the requirements of WiMax, WiBro, or a similar consortium. In another embodiment, network device  501  is an 800 MHz or 1900 MHz base station. In yet another embodiment, the system is a cellular/PCS system and network device  501  communicates with a base station controller. In still another embodiment, network device  501  communicates with a voice/PSTN gateway. The network device  501  also creates the protocol and modulation type for the channel. In packet networks, the network device  501  converts the packetized data into an analog RF signal for transmission via antenna assemblies  508 . 
     The network device  501  sends the RF signal to host unit  502 . The host unit  502  converts the analog RF signal to a digital serial data stream for long distance high speed transmission over transport mechanism  504 . The host unit  502  sends the serial data stream over the signal transport mechanism  504 , and the stream is received by one or more RAUs  506 . Each RAU  506  converts the received serial data stream back into the original analog RF signal and transmits the signal over its corresponding antenna assembly  508  to consumer mobile devices  510  (for example, a mobile station, fixed wireless modem, or other wireless devices). In some embodiments, the upstream devices, such as network device  501 , are a part of a telecommunication-service providers&#39; infrastructure while the downstream devices, such as wireless devices  510 , comprise customer premise equipment. 
     In addition, in some embodiments, the host unit  502  is directly physically connected to one or more upstream network devices  501 . In other embodiments, the host unit  502  is communicatively coupled to one or more upstream devices in other ways (for example, using one or more donor antennas and one or more bi-directional amplifiers or repeaters). Furthermore, the host unit  502  and/or RAUs  506  may perform one or more of the following: filtering, amplification, wave division multiplexing, duplexing, synchronization, and monitoring functionality as needed. 
     Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement, which is calculated to achieve the same purpose, may be substituted for the specific embodiments shown. For example, dimensions, types of materials, orientations of the various components, and the number and positions of the various components described herein are intended to define parameters of certain embodiments, and are by no means limiting and are merely exemplary embodiments. As used herein, the terms “first,” “second,” and “third,” etc. are used as labels and are not intended to impose numerical requirements on their respective objects. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof.