Patent Publication Number: US-10790576-B2

Title: Multi-band base station antennas having multi-layer feed boards

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority under 35 U.S.C. 119 to U.S. Provisional Patent Application Ser. No. 62/266,948, filed Dec. 14, 2015, the entire content of which is incorporated herein by reference as if set forth in its entirety. 
    
    
     BACKGROUND 
     Antennas operating in certain frequency bands may include an array of radiating elements connected by a feed network. The feed network may include a series of functional components that are positioned on various feed boards that are coupled together with coaxial cables. Solder joints are often used as interfaces to connect the coaxial cables to the functional components of the various feed boards. To accommodate increasing wireless demands, antennas are increasing in complexity, resulting in more functional components and more solder joint interfaces electrically connecting the same, among the various feed boards, increasing susceptibility to passive intermodulation (PIM) issues. 
     SUMMARY OF THE DISCLOSURE 
     Various aspects of the present disclosure may be directed to multi-band antennas that transmit and receive signals in at least two different frequency bands that include multi-layer feed board with the functional components, including phase shifters, diplexers, and dipole element, employed thereon. Therefore, solder interfaces at cable-to-functional component interfaces are no longer necessary. Instead, component interfaces are within the confines of the multi-layer feed board, thereby reducing PIM issues attributed to solder joint interfaces. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The following detailed description of the disclosure will be better understood when read in conjunction with the appended drawings. For the purpose of illustrating the disclosure, example embodiments are shown in the drawings. It should be understood, however, that the disclosure is not limited to the precise arrangements and instrumentalities shown in the drawings. 
         FIGS. 1A and 1B  are plan views of examples of double-sided feed boards of a base station antenna in a multiple multi-layer feed board arrangement, according to an aspect of the present disclosure; 
         FIG. 2  is an exploded perspective view of the base station antenna of  FIGS. 1A and 1B , according to an aspect of the present disclosure; 
         FIG. 3  is an exploded perspective view of a base station antenna employing a single multi-layer feed board according to an aspect of the present disclosure; 
         FIGS. 4A and 4B  are plan views of back and front sides of a reflector of the base station antenna according to an aspect of the present disclosure; 
         FIGS. 5A and 5B  are plan views of first and third layers, respectively, of the multi-layer feed board according to an aspect of the present disclosure; 
         FIG. 6A  is an enlarged view of a portion of the first layer and the third layer of the multi-layer feed board, according to an aspect of the present disclosure; 
         FIG. 6B  is an enlarged view of another portion of the first layer and the third layer of the multi-layer feed board, according to an aspect of the present disclosure; 
         FIG. 6C  is an enlarged view of a portion of the multi-layer feed board incorporating actuation systems, according to an aspect of the present disclosure; 
         FIG. 6D  is an enlarged view of a portion of an underside of the multi-layer feed board according to an aspect of the present disclosure; 
         FIG. 7  is an illustration of an example of a stack up of the multi-layer feed board according to an aspect of the present disclosure; 
         FIGS. 8A and 8B  are perspective views of the multi-layer feed board according to an aspect of the present disclosure; 
         FIG. 9  is a block diagram illustrating an arrangement of phase shifters for a 6 foot multi-layer feed board according to an aspect of the present disclosure; 
         FIG. 10A  is a plan view of the 6 foot multi-layer feed board according to an aspect of the present disclosure; 
         FIG. 10B  is an enlarged view of a portion of the 6 foot multi-layer feed board according to an aspect of the present disclosure; 
         FIG. 11A  is a plan view of an 8 foot multi-layer feed board according to an aspect of the present disclosure; and 
         FIG. 11B  is an enlarged view of a portion of the 8 foot multi-layer feed board according to an aspect of the present disclosure; 
     
    
    
     DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS 
     Certain terminology is used in the following description for convenience only and is not limiting. The words “lower,” “bottom,” “upper” and “top” designate directions in the drawings to which reference is made. Unless specifically set forth herein, the terms “a,” “an” and “the” are not limited to one element, but instead should be read as meaning “at least one.” The terminology includes the words noted above, derivatives thereof and words of similar import. It should also be understood that the terms “about,” “approximately,” “generally,” “substantially” and like terms, used herein when referring to a dimension or characteristic of a component of the disclosure, indicate that the described dimension/characteristic is not a strict boundary or parameter and does not exclude minor variations therefrom that are functionally similar. At a minimum, such references that include a numerical parameter would include variations that, using mathematical and industrial principles accepted in the art (e.g., rounding, measurement or other systematic errors, manufacturing tolerances, etc.), would not vary the least significant digit. 
     Antennas operating in certain frequency bands (e.g., 880-960 MHz, 1710-1880 MHz, 1920-2170 MHz, 2.5-2.7 GHz, 3.4-3.8 GHz, etc.) may include an array of radiating elements that is connected to one or more radios by a feed network. The feed network may include a series of functional components that are positioned on various feed boards. The feed boards are coupled together with coaxial cables. For example, phase shifters, diplexers, power dividers, and other antenna components may be implemented on different feed boards (e.g., printed circuit boards) of antennas (e.g., base station antennas). The number of antenna components as well as the number of feed boards may increase as the complexity of the antenna increases. For example, to accommodate increased wireless traffic, some antennas, which are referred to herein as “multi-band” antennas, may be configured to operate in more than one frequency band. Solder joint interfaces may electrically connect the antenna components on the various feed boards. 
     For example, referring to  FIGS. 1A and 1B , plan views of two double-sided feed boards of a base station antenna  100  are respectively shown. More specifically, as shown in FIG.  1 A, one double-sided feed board  102  includes conductive traces for signaling operation in one frequency band (e.g., a low band), and another double-sided feed board  104  (shown in  FIG. 1B ) includes conductive traces for signaling operation in another frequency band (e.g., a high band). With such a configuration, two diplexer boards  106 ,  108  (as shown in  FIG. 1A ) may also be necessary. Consequently, in total, at least four boards are employed. Portions of these boards may need to be connected to one another through solder joints. Even though several of these boards employ multiple layers to implement components on the same feed board (and thus exhibit some of the same benefits of other aspects of the present disclosure described below), there are nonetheless many solder joints used to connect the antenna components implemented on the different feed boards. In other designs, an increased number of printed circuit boards are required, and, in turn, a greater number of solder joints may be required to connect the antenna components. Solder joints are known to be a source of passive intermodulation (PIM) instability, potentially decreasing the yield in the fabrication of the antenna. Moreover, solder joints are typically constructed by hand (“hand soldering”). Hand soldering is known to be a tedious process and can increase variability in electrical interfaces. 
       FIG. 2  is an exploded perspective view of the base station antenna  100  of  FIGS. 1A and 1B . As shown, the low band feed board  102  is positioned on one side of a reflector  110  of the base station antenna  100 , while the high band feed board  104  is positioned on the other side of the reflector  110 . Such a configuration may result in high back radiation, or radiation in a direction opposite the main lobe. 
       FIG. 3  is an exploded perspective view of a multi-band base station antenna  300  that is implemented using a single multi-layer feed board  302  with all the functional components, including phase shifters, diplexers, and radiating elements, employed thereon. For example, antenna components associated with operation in a first frequency band, as well as antenna components associated with operation in a second frequency band may be employed on the same multi-layer feed board  302  on one side of a reflector  304 . Therefore, the number of solder interfaces at cable-to-functional component interfaces may be reduced since these component interfaces may be within the confines of the multi-layer feed board  302 . This may reduce PIM issues attributed to solder joint interfaces. Any remaining essential solder joints may be constructed via an automated soldering process, such as a selective wave flow soldering process. 
       FIGS. 4A and 4B  are plan views of back and front sides of the reflector  304 , respectively, of the base station antenna  300 , according to an aspect of the present disclosure. As shown in  FIGS. 4A and 4B , there is no feed board on the opposite side of the reflector  304 , reducing the likelihood of any PIM issues due to back radiation. 
     Referring to  FIGS. 5A and 5B , various layers of the multi-layer feed board  302  are illustrated.  FIG. 5A  is a plan view of a first layer  501  (e.g., a top layer) of the multi-layer feed board  302 . The first layer  501  includes a plurality of microstrip transmission lines (“conductive traces”)  504  that electrically connect various antenna components including first frequency band phase shifters  502  for phase shifting first frequency band signals. The first layer conductive traces  504  may electrically couple outputs of the first frequency band phase shifters  502  to first frequency band radiating elements  506  (shown in  FIGS. 8A and 8B ). The first frequency band phase shifters  502  may be configured to phase shift sub-components of the first frequency band signals. Also located on the first layer are second frequency band phase shifters  508  for phase shifting sub-components of second frequency band signals, and first and second diplexers  510 ,  512 . The first and second frequency band phase shifters  502 ,  508  may be implemented using printed circuit board fabrication techniques. Rotatable wiper arms for the first and second frequency band phase shifters  502 ,  508  are not illustrated to enhance clarity of the fixed portions of the first and second frequency band phase shifters  502 ,  508 . The first and second frequency band phase shifters  502 ,  508  may comprise variable differential, arcuate phase shifters as described in U.S. Pat. No. 7,907,096, which is incorporated herein by reference. It should be noted, however, that the first and second frequency band phase shifters  502 ,  508  may take the form of other types of phase shifters in keeping with the disclosure. Having the first and second diplexers  510 ,  512  as well as the first and second frequency band phase shifters  502 ,  508  on the same feed board  302  may eliminate the need for additional solder joint interfaces among multiple feed boards. 
       FIG. 5B  is a plan view illustrating another layer, e.g., a third layer  514  (e.g., located below the first layer) of the same feed board  302 . As shown, third layer conductive traces  516  may electrically connect various components including outputs of the second frequency band phase shifters  508  to second frequency band radiating elements  518  (shown in  FIGS. 8A and 8B ) associated with a second frequency band operating range of the base station antenna  300 . 
       FIG. 6A  is an enlarged view of a portion of the first layer  501  including the first layer conductive traces  504  of  FIG. 5A , with third layer conductive traces  516  (shown in dashed lines). Input cable solder joint locations  519  are shown. Coaxial cables may be mounted at these input cable solder joint locations  519  and soldered in place to physically and electrically attach such cables to the multi-layer feed board  302 . The input cable solder joint locations  519  are electrically connected to respective inputs of the first and second diplexers  510 ,  512 . Plated through holes may be employed to connect respective outputs  524 ,  526  of the first and second diplexers  510 ,  512  to the third layer conductive traces  516 . 
       FIG. 6B  is an enlarged view of another portion of the first layer  501  of the multi-layer feed board  302 . Plated though holes may also be employed to electrically couple one or more outputs of the first and second diplexers  510 ,  512  (as shown in  FIG. 6A ) to respective inputs of the first band phase shifters  502 . Other outputs of the first and second diplexers  510 ,  512  may be connected to the second band phase shifters  508  (shown in  FIG. 5A ). 
     As shown in  FIG. 6C , the multi-layer feed board  302  may incorporate actuation systems for remote electrical tilt, a lightning protection module (which may hold AISG connectors as well as circuitry that protects the system from voltage surges such as lightning strikes), and/or a combined smart bias Tee  602 , which may also serve to eliminate electrical interfaces, cables, and connectors. These components, as well as one or more others discussed herein, may be mounted to the multi-layer feed board  302  through surface mounting, and reflow soldering techniques. After reflow soldering, the multi-layer feed board  302  may be subjected to a selective wave flow solder process to solder the radiating elements  506 ,  518  to the multi-layer feed board  302 . Using techniques such as selective wave flow soldering, the temperature of the multi-layer feed board  302  may remain relatively low during the soldering, thus preventing the components from again reflowing. Also, input connectors can be soldered to the multi-layer feed board  302  during wave soldering to eliminate additional hand solder joints and improve PIM, reliability and assembly time. 
     As shown in  FIG. 6D , one or more plated through holes  604  may be employed to connect conductive traces to a ground layer for allowing wave soldering at a bottom side of the multi-layer feed board  302 . 
       FIG. 7  is an illustration of a stack-up of the multi-layer feed board  302  according to an aspect of the present disclosure. The multi-layer feed board  302  may comprise layers of different materials stacked on top of each other, which include the above discussed first signal layer (“Layer  1 ”) and third signal layer (“Layer  3 ”). These layers, along with other layers, which may be ground layers, such as Layer  2  and Layer  4 , may take the form of copper microstrip lines. These four layers may be separated by other layers, such as insulating layers. Having multiple routing layers allows for isolation between high frequency band and low frequency band signals as well as avoidance of the need to cross over conductive traces. 
       FIGS. 8A and 8B  are perspective views of the multi-layer feed board  302  with various radiating elements  506 ,  518  mounted thereon. The first set of radiating elements  506  may comprise, for example, a first linear array of crossed dipole elements and may be dimensioned for transmission and/or reception of radio frequency (RF) signals in the first frequency band. The second set of radiating elements  518  may comprise a second linear array of microstrip annular ring elements arranged on a longitudinal axis, and may be dimensioned to transmit and/or receive RF signals in the second frequency band. In this example, the first set of radiating elements  506  may comprise high band elements (e.g., for operation in frequency band 1695-2690 MHz). The second set of radiating elements  518  may comprise low band elements (e.g., for operation in frequency band 694-960 MHz). The first layer conductive traces  504  may be directly fed to the first set of radiating elements  506 . The crossed dipole elements  506  may be interspersed with the annular ring elements  518 . The crossed dipole elements  506  may be oriented so that the dipole elements are at approximately +45 degrees to vertical and −45 degrees to vertical to provide polarization diversity. The annular ring elements  518  may have two +/−45 degree polarizations, and may be also be used to provide polarization diversity. As best seen in  FIG. 8B , the third layer conductive traces  516  may feed the second set of radiating elements  518 . 
     Other types of radiating elements may be employed in keeping with the spirit of the disclosure. For example, box dipole elements may be substituted for the crossed dipole elements. In another example, box dipole elements may be substituted for the microstrip annular ring elements. In yet another example, dual-polarized patch elements, as described in U.S. Pat. No. 6,295,028, the contents incorporated herein by reference, may be used for both the first and second frequency bands. 
     Aspects of the disclosure may be implemented with multi-layer feed boards of various lengths including, but not limited to 2 foot feed boards (such as described above), 6 foot, 8 foot, and greater length feed boards. With feed boards having lengths greater than 2 feet, one of the 2 foot multi-layer feed boards may take the form of a main feed board configured to feed the other 2 foot feed board portions. A block diagram of such an arrangement of the phase shifters for a 6 foot multi-layer feed board ( 800  as shown in  FIG. 10 ) is shown in  FIG. 9 . The main feed board may include primary phase shifters  802 , which may include one or more phase shifters for low band and high band phase shifting. Outputs of the primary phase shifters  802  may be coupled to inputs of phase shifters of the other multi-layer feed board portions. For example, two outputs of the primary phase shifter may be coupled to respective inputs of secondary phase shifters  804  employed on a second 2 foot multi-layer feed board portion. Another two outputs of the primary phase shifter  802  may be coupled to respective inputs of tertiary phase shifters  806  employed on a third 2 foot multi-layer feed board portion. As shown in the plan view of the 6 foot multi-layer feed board of  FIG. 10A  and the enlarged view of a portion of the same in  FIG. 10B , the above discussed connections may be made via jumpers from the first 2 foot multi-layer feed board portion to the additional board portions. A similar arrangement may be applied to 8 foot multi-layer boards as well, an example multi-layer feed board  900  of which is shown in  FIGS. 11A and 11B . More specifically, as shown, main board phase shifters PSI may include four outputs, one of which to feed phase shifters on the main board, 2 nd  and 3 rd  outputs to two middle 2 foot multi-layer board portions, and a 4 th  output to the last 2 foot multi-layer board portion. 
     Various aspects of the disclosure have now been discussed in detail; however, the disclosure should not be understood as being limited to these embodiments. It should also be appreciated that various modifications, adaptations, and alternative embodiments thereof may be made within the scope and spirit of the present disclosure.