Patent Publication Number: US-6983174-B2

Title: Distributed active transmit and/or receive antenna

Description:
FIELD OF THE INVENTION 
     This invention is directed generally to active antennas, and more particularly, to transmit and receive array antennas, such as those used in connection with cellular radio applications. 
     BACKGROUND OF THE INVENTION 
     Numerous communications applications, such as cellular and personal communications services (PCS), as well as multi-channel multi-point distribution systems (MMDS) and local multi-point distribution systems (LMDS), conventionally receive and retransmit signals from subscribers utilizing antennas mounted at the tops of towers or other structures. Other communications systems such as wireless local loop (WLL), specialized mobile radio (SMR), and wireless local area network (WLAN), have signal transmission infrastructure for receiving and transmitting communications between system subscribers that similarly utilize various forms of antennas and transceivers. 
     All of these communications systems require amplification of the signals being transmitted by the antennas. For this purpose, it has heretofore been the practice to use a conventional linear power amplifier system placed at the bottom of the tower or other structure upon which the antennas are mounted. From the base of the tower, the conventional linear power amplifier system typically couples to the antenna elements mounted on the tower with coaxial cables. Coaxial cables, however, introduce power losses that are proportional to length. To overcome these power losses, substantial amplification is typically required, which necessitates the use of more expensive, higher power amplifiers. 
     Moreover, the diameter of the cables must generally be of a low loss variety to mitigate insertion losses. In addition to increasing system material costs, the low loss cables characteristically have large diameter cross-sections. Thus, along with the relatively long length of cable required by the system configuration, the large diameter of the cables can contribute towards making a system vulnerable to damage sustained from high wind conditions. That is, the dimensions of the cables increase the wind friction experienced by the system. 
     The size and number of coaxial cables further require reinforcement of the tower structure to accommodate loading forces associated with the weight of the cables. System architects may consequently implement costly preventative design features and expect periodic cable disconnections and other repairs. 
     As discussed herein, insertion losses associated with the cables may necessitate some increases in the power amplification. A ground level infrastructure or base station typically provides the compensatory amplification, thus further increasing the expense per unit or cost per watt. Of note, output power levels for infrastructure (base station) applications in many of the foregoing communications systems are typically in excess of ten watts, and often up to hundreds of watts, which results in a relatively high effective isotropic power requirement (EIPR). 
     For example, for a typical base station with a twenty-watt power output (at ground level), the power delivered to the antenna, minus cable losses, is around ten watts. In this case, half of the power has been consumed in cable loss/heat. Such systems require complex linear amplifier components cascaded into high power circuits to achieve the required linearity at the higher output power. Typically, for such high power systems or amplifiers, additional high power dividers must be employed. Operating characteristics of such divider equipment may introduce further insertion losses associated with the equipment, itself. 
     Some of such losses are addressed in certain instances by positioning amplification equipment closer to the antenna(s) on the tower mast. While helpful in mitigating some insertion losses associated with cables running up the towers to the antenna(s), such placement of the amplifiers still fails to address insertion losses associated with the jumper cable that connects the amplifier to the antenna, as well as any power divider disposed therebetween. Moreover, even where an antenna has multiple elements, those elements are typically coupled to and serviced by a common amplifier and divider. Thus, failure of a single amplifier, divider or other amplifying component may effectively render the entire system inoperable. In this manner, the reliability of a system having multiple elements remains undermined by the collective dependence of the respective elements on common components. Furthermore, the relative inaccessibility of the amplification equipment attributable to its proximity to the to the tower mast can compound repairs and other maintenance. Consequently, inefficiencies associated with insertion losses continue to hinder operation and result in a relatively high cost of unit per watt. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description of the embodiments given below, serve to explain the principles of the present invention. 
         FIG. 1  shows an antenna system in accordance with the principles of the present invention; 
         FIG. 2  is a block diagram of an antenna assembly including two sets of duplexers, and having application within the system of  FIG. 1 ; 
         FIG. 3  is a block diagram of an antenna assembly including circulators, and having application within the antenna system of  FIG. 1  in accordance with another aspect of the invention; 
         FIG. 4  is a block diagram of the antenna assembly of  FIG. 3 , and including an additional duplexer in accordance with another aspect of the invention; 
         FIG. 5  is a block diagram of an antenna assembly including distributed power amplifiers, and having additional application within the antenna system of  FIG. 1  in accordance with another aspect of the invention; 
         FIG. 6  is a block diagram of the antenna assembly of  FIG. 5 , and including an additional duplexer in accordance with another aspect of the invention; and 
         FIG. 7  is a block diagram of an antenna assembly including distributed power amplifiers and two sets of duplexers, and having application within the antenna system of  FIG. 1  in accordance with another aspect of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The invention addresses the above-discussed problems associated with the prior art by providing an antenna system  10  configured to improve cellular system performance by, in one respect, mitigating the occurrence of insertion losses through the use of an antenna incorporating an array of antenna elements and distributed amplifiers coupled to those individual elements in the array. 
     Referring generally to  FIG. 1 , there is shown an exemplary antenna system  10  in accordance with the precepts of the present invention. In order to achieve lower incidence of insertion loss, the antenna system  10  uses amplification equipment  11  disposed at the antenna element level. As such, exemplary antenna system  10  typically includes a plurality of beam width antenna arrays  13  suspended by a tower  16  or other support structure. Each antenna array  13  may include a plurality of antenna elements  12 . The antenna arrays  13  may attach proximate the top  14  of the tower  16 . Tower  16  may be supported by a base  18 , a portion of which is typically buried in the ground  20 . Exemplary amplification equipment  11  may include at least one amplifier or comparable device suited to discriminate between desired signals and spurious radiation and/or a device configured to increase the strength of an electronic impulse. 
     Antenna system  10  may further include a control or base station  22  in electrical communication with the antenna elements  12 . Of note, embodiments of the present invention may allow the antenna elements  12  to communicate with the control station  22  via small diameter (i.e. not low-loss) cable. Utilization of the small diameter cable can reduce system  10  costs and wind load complications. Of note, while control station  22  may stand adjacent tower  16 , the exemplary antenna system  10  depicted in  FIG. 1  includes a remotely situated control station  22 . A telecommunications system consistent with the principles of the present invention may further collocate control station  22  with a central office (not shown) for reasons of convenience. While such a configuration as shown in the exemplary system  10  of  FIG. 1  has particular application in the context of embodiments of the present invention, one skilled in the art should appreciate that the number, presence, and arrangement of the exemplary components  11 – 22  of the antenna system  10  may be altered substantially and still remain with the confines of the present invention. 
     In the illustrated embodiment of  FIG. 1 , amplification equipment  11 , which may include one or more low noise amplifiers, is placed at or near the tower top  14  to combat insertion losses. Namely, positioning of the amplification equipment  11  near the tower top  14  may obviate the requirement that a cable connecting the antenna elements  12  to a low noise amplifier run the entire length of the tower  16 . Furthermore, an embodiment of the present invention may place respective low noise amplifiers at each antenna element  12 . The distributed arrangement of the amplification equipment  11  may further eliminate much of the insertion losses conventionally associated with the above-discussed jumper cables. 
     Still other embodiments of the antenna system  10  shown in  FIG. 1  may mitigate insertion losses associated with conventional power dividers as discussed below in the text describing  FIGS. 2–7 . Moreover, because the active elements are distributed at the antenna element level, the system  10  can withstand one or more low noise amplifier failures with minimal impact to noise figure performance. Noise figure performance generally regards the signal-to-noise ratio and relates directly to signal clarity and other desirable operating characteristics. 
     To this end,  FIG. 2  shows an amplification system  30  and associated array of antenna elements  12  suited for application within the antenna system environment of  FIG. 1 . As above, suitable antenna elements  12  may include virtually any device configured to transmit and/or emit electromagnetic radiation. As such, the antenna elements  12  may typically service cellular, paging and other applications. Notably, the amplification system  30  of  FIG. 2  incorporates both first and second sets of duplexers  32 ,  40 , respectively. The duplexer sets  32 ,  34  cooperate with other amplification components  48 ,  54  to realize performance gains that reduce incidences of noise, as well as insertion loss conventionally associated with a power divider  54 . 
     Of note, a suitable duplexer  32 ,  40  for purposes of the present embodiment may include any device configured to facilitate two-way signal transmission. In one embodiment, the duplexers  32 ,  40  and at least one low noise amplifier  48  may be collocated proximate the top  14  of a tower structure  16  supporting the plurality of antenna elements  12 . Such concentrated placement may function to further reduce insertion losses associated with conventional, lengthy cables. The distributed arrangement of the duplexers  32 ,  40 , antenna elements  12  and low noise amplifiers  48  may additionally contribute to the robustness of the system  30  by virtue of the each antenna element  12  not being collectively dependent upon a single amplification component  11 . 
     As employed in  FIG. 2 , the low noise amplifiers  48  or other comparable filtering/amplification device may function to both discriminate between and bolster the strength of processed signals. As shown in  FIG. 2 , the low noise amplifiers  48  typically operate between respective antenna elements  12  and at least one power divider  54 . As such, the low noise amplifiers  48  may select and output to the power divider  54  a desired signal or group of signals determined from among those received from respective antenna elements  12 . For purposes of this disclosure, a suitable power divider  54  may comprise any device configured to apportion and/or combine electrical signals. Thus, the power divider  54 , in one respect, may combine respective outputs from the plurality of low noise amplifiers  48  corresponding to the received signals. 
     The amplification system  30  of  FIG. 2  includes a first set of duplexers  32  proximate the plurality of antenna elements  12 . Each duplexer  32  of the first set may have at least one receive port  36 , one antenna port  34  and one transmit port  38 . These respective ports  34 ,  36  and  38  of the duplexers  32  may accommodate two-way signal transmission desirable for operation of the antenna elements  12 . To this end, the antenna ports  34  of the first set of each duplexer  32  may couple to respective antenna elements  12  of the plurality of antenna elements. As such, the first set of duplexers  32  are positioned to receive and communicate signals to the low noise amplifiers  48  from the antenna elements  12 . Moreover, the duplexers  32  may be configured to simultaneously convey signals arriving at their receive ports  36  to the antenna elements  12  for subsequent downlink transmission. 
     Each duplexer  40  of the second set of duplexers may likewise have at least one receive port  46 , one transmit port  44  and one antenna port  42 . As in the embodiment shown in  FIG. 2 , the respective receive ports  36  of the first set of duplexers  32  may couple to the respective transmit ports  44  of the second set of duplexers  40 . That is, signals output from a duplexer  40  of the second set may feed an antenna element  12  via a corresponding duplexer  32  of the first set. 
     The amplification system  30  of  FIG. 2  may further include a plurality of low noise amplifiers  48 . For purposes of this disclosure, a suitable low noise amplifier  48  in accordance with the principles of the present invention may include any device useful in discriminating between desired signals and spurious radiation and/or suited to bolster a received signal. In accordance with one embodiment of the present invention, each low noise amplifier  48  may have at least one input  50  and output  52 . The input  50  of each low noise amplifier  48  may couple to a respective transmit port  38  of the first set of duplexers  32 . 
     The output  52  of each low noise amplifier  48  may, in turn, couple to a respective receive port  46  of the second set of the plurality of duplexers  40 . As such, signals from the duplexers  32  of the first set of duplexers may drive the output of each low noise amplifier  48  as supplied to respective duplexers  40  of the second set. In one embodiment, at least one power divider  54  may couple to respective antenna ports  42  of the second set of the plurality of duplexers  40 . Thus, the power divider  54  may be configured to simultaneously accommodate signals intended for transmission at the antenna elements  12 , as well as those transmitted to the duplexers  40 . Accordingly, the power divider  54  may simultaneously combine signals received from the antenna elements  12  via the low noise amplifiers  48  and duplexers  40 . Of note, another embodiment consistent with the underlying principles of the invention may include multiple power dividers  34  as dictated by space, performance and other system  30  preferences. 
     In this manner, the embodiment shown in  FIG. 2  reduces incidences of insertion loss associated with transmission and jumper cables of conventional systems. The configuration of the amplification system  30  similarly minimizes insertion losses attributable to power dividers in known antenna systems. Cumulative improvements realized by the amplification system  30  of  FIG. 1  may further realize signal improvements regarding the signal to noise ratio on the order of 1.5 decibels (dB). Additionally, embodiments of the present invention may improve system reliability relative to conventional applications by virtue of the low noise amplifiers  48  and duplexers  32  being distributed among multiple antenna elements  12 . Thus, the amplification system  30  can withstand one or more low noise amplifier  48  failures with minimal impact to signal quality. 
     Similar advantages may be realized using the antenna configuration shown in  FIG. 3 . As with the embodiment of  FIG. 2 , the amplification system  30  may have application within the tower structure and antenna environment of  FIG. 1 . The exemplary amplification system  60  of  FIG. 3  notably achieves duplexing at the antenna element level. To this end, the amplification system  60  may rely on a plurality of circulators  62 , duplexers, or other device(s) suited to realize common voltages across incoming signal lines and/or otherwise enable two-way signal transmission. Of note, the antenna system  60  features separate transmit and receive cables  70 ,  75 , respectively. Inclusion and separation of the separate cables  70 ,  75  may accommodate desirable cable sizes having distinct and advantageous characteristics. That is, the presence of a plurality of low noise amplifiers  64  may enable the receive cable  70  to be of a high-loss/low power rating having a cross-sectional small diameter. Use of such cabling may save manufacturing and maintenance costs, while reducing damaging effects resulting from wind load. 
     Turning more particularly to  FIG. 3 , the amplification system  60  includes antenna elements  12  typically configured to receive and transmit electromagnetic radiation. As such, the amplification system  60  of  FIG. 3  may have application as or in conjunction with the amplification equipment  11  comprising part of the antenna system  10  of  FIG. 1 . The amplification system  60  of  FIG. 3  may further include a plurality of circulators  62  or other duplexers, each having respective antenna ports  67  coupled to respective antenna elements  12 . As discussed herein and for purposes of this disclosure, the functionality of the circulators  62  may be supplanted by any device configured to match impedance and/or otherwise enable two-way passage of signals two and from the antenna elements  12 . Moreover, each circulator  62  may include respective receive ports  63  and transmit ports  65 . The low noise amplifiers  64  may each have an output  72  and an input  74 . The input of each low noise amplifier  64  may couple to the transmit port  65  of a respective circulator  62  of the plurality of circulators. 
     One embodiment consistent with the principles of the present invention may include at least one combiner  68  within the amplification system  60  of  FIG. 3 . As such, each the at least one combiner  68  may couple to and sum the respective outputs  72  of the low noise amplifiers  64 . Another or the same embodiment may include at least one power divider  76  coupled to the respective receive ports  63  of each circulator  62 . A power divider  76  consistent with the principles of the present invention may apportion a transmission signal originating from a base station  22  and intended for the antenna elements  12 . 
     Of note, the antenna system  60  may further include one or more band pass filters  78  coupled to both the respective input  74  of each low noise amplifier  64  and to the transmit port  65  of each circulator  62 . Thus, the signals outputted from the antenna elements  12  and passing through the circulators  63  are filtered prior to processing at the low noise amplifiers  64 . One skilled in the art should appreciate that while separate circulators  62  are shown coupled to each antenna element  12  in  FIG. 3 , another embodiment consistent with the underlying principles of the present invention may rely on more or fewer duplexer equivalents, to include one circulator  62  or duplexer coupled to more than one antenna elements  12  of the plurality of antenna elements. 
     An embodiment of the amplification system  80  shown in  FIG. 4  couples a duplexer  82  to the combiner  68  and power divider  76  included in the amplification system  60  of  FIG. 3 . In this manner, the duplexer  82  of  FIG. 4  facilitates two-way communication of signals two and from the base station  22 . Of note, the antenna system  80  of  FIG. 4  may function where preferred in the absence of the power divider  76  in accordance with the underlying principles of the present invention. As such, the single duplexer  82  may couple to at least one combiner  68  and to the receive port  63  of at least one duplexer  62  of the plurality of duplexers. The configuration of the antenna system  80  of  FIG. 4  may in this manner achieve significant signal performance gains with minimal filtering. The absence of such filtering requirements and associated equipment can translate into reduced production, maintenance and operating costs. 
     The transmission paths shown in the embodiments of  FIGS. 2–4  may be implemented in a number of manners consistent with the invention. For example, amplification of the transmission paths may be performed by a single amplifier positioned at the base station or at the tower top. Alternatively, as exemplified by the system  90  of  FIG. 5 , a plurality of power amplifiers  102 , positioned in a distributive arrangement with respect to the antenna elements  12 , may be used to provide amplification for the transmission paths for the various antenna elements  12 . 
     As with the embodiment shown in  FIG. 2 , the amplification system  90  shown in  FIG. 5  realizes greater system efficiently, power savings and improved signal quality by virtue of placing a plurality of low noise and power amplifiers  92 ,  94 , respectively, as well as duplexers  96  proximate the antenna elements  12 . As shown in  FIG. 5 , amplification system  90  includes a plurality of antenna elements  12 , which may or may not resemble antenna elements discussed in the above-illustrated embodiments. Thus, the amplification system  90  illustrated in  FIG. 5  may also have application within the antenna system  10  of  FIG. 1 . 
     An embodiment of amplification system  90  includes a plurality of low noise amplifiers  92 . As above, while the low noise amplifiers  92  shown in  FIG. 5  may have particular application in the context of certain operating scenarios, other devices suited to discriminate between signals and/or increase signal strength may be substituted in their place in accordance with the principles of the present invention. Each low noise amplifier  92  may have an input  98  and an output  100 . The antenna system  90  may additionally include a plurality of power amplifiers  94 . Each power amplifier may be configured to boost signal strength, and have an associated input  102  and an output  104 . 
     As shown in  FIG. 5 , the system  90  may include a plurality of duplexers  96  coupled to respective antenna elements  12 . More particularly, an antenna port  110  of each duplexer  96  may couple to the antenna elements  12 , which are configured to receive and transmit electromagnetic radiation. As such, the duplexer  96  enables the antenna element  12  to simultaneously receive and transmit signals. Accordingly, a transmit port  108  of each duplexer  96  may couple to respective inputs  98  of each low noise amplifier  92 . Thus, the duplexer  96  is configured to pass signals from the antenna elements to the low noise amplifiers  92  on their way to the base station  22 . Outputs  104  of the power amplifiers  94  of one embodiment couple to respective input ports  106  of each duplexer  96 . In this manner, the duplexer  96  passes the bolstered signals outputted from the power amplifiers  94  to respective antenna elements  12  for subsequent transmission. 
     The exemplary antenna system  90  of  FIG. 5  may also rely on at least one combiner  112  to sum the respective outputs  100  of each low noise amplifier  92 . Thus, the signals filtered and conveyed from the antenna elements  12  via the low noise amplifiers  92  are combined prior to reception at the base station  22 . One or more power dividers  114  may additionally couple to the respective inputs  102  of each power amplifier  94 . In this manner, signals from the base station  22  are apportioned prior to amplification and subsequent transmission at antenna elements  12 . Of note, active elements  92 ,  94 ,  96  are typically positioned at the antenna element level to realize the above-discussed advantages. 
     The amplification system  116  of  FIG. 6  is similar to the amplification system of  FIG. 5  in most respects, except for the inclusion of a common duplexer  118 . The duplexer  118  couples to both the combiner  112  and the power divider  114 . One embodiment of the amplification system  116  may include the duplexer  118  for the purpose of enabling separate receive and transmit signals to pass over a single cable coupled to both the duplexer  118  the base station  22 . 
     The amplification system  130  shown in  FIG. 7  may achieve many of the above-discussed advantages while utilizing a single power divider  132 . An embodiment of the amplification system  130  thus necessitates only a single transmission cable  131 . The antenna system  130  may additionally include a plurality of antenna elements  12 . As with all of the above-discussed embodiments, suitable antenna elements  12  may be configured to both receive and transmit electromagnetic radiation and may include other functionality as dictated by operating criteria. Similarly, a power divider  132  consistent with the principles of the present invention may include any device configured to either or both apportion or sum received signals. 
     The amplification system  130  may further include a plurality of low noise amplifiers  134  in communication with both the antenna elements  12  and the power divider  132 . More particularly, each low noise amplifier may be configured to discriminate between different signals being transmitted, or uplinked, to a base station  22 . As such, each low noise amplifier  134  may have an input  136  and an output  138  with which to respectively receive and transmit processed signals. As shown in  FIG. 7 , a plurality of power amplifiers  140  may also be included in the exemplary antenna system  130 . Accordingly, each power amplifier  140  may have an input  142  and an output  144 . 
     The embodiment shown in  FIG. 7  may also include two sets of duplexers  146 ,  154 . The first set of duplexers  146  may couple to at least the antenna elements  12 . To this end, each duplexer  146  of the first set may have at least one antenna port  152 . Accordingly, each antenna port  152  may couple to a respective antenna element  12  of the plurality of antenna elements. Each duplexer  146  may also include at least one receive port  148  and one transmit port  150 . Transmit ports  150  of each duplexer  146  of the first set may, in turn, couple to respective inputs  136  of each low noise amplifier  134 . Thus, the duplexer  146  brokers signals from the antenna elements  12  to the low noise amplifiers  134 . The low noise amplifiers  134  may subsequently determine and output the most desirable antenna signal(s) from those received from the duplexer  146 . Receive ports  148  of each of the first set of the plurality of duplexers  146  may couple to the output  144  of the respective power amplifier  140  of the plurality of power amplifiers. As such, the duplexers  146  may pass amplified signals received from the power amplifiers  140  to the antenna elements  12  for downlink transmission. 
     Each duplexer  154  of the second set of the plurality of duplexers may likewise include at least one receive port  156 , transmit port  158  and antenna port  160 . The receive port  156  of each of the second set of duplexers  154  may couple to the output  138  of a respective low noise amplifier  134 . Moreover, transmit ports  158  of each of the second set of the plurality of duplexers  154  may couple to the inputs  142  of respective power amplifiers  140 . Finally, the respective antenna ports  160  of each of the second set of duplexers  154  may couple to at least the power divider  132 . 
     In this manner, the duplexers  154  allow signals to pass from the power divider  132  to the antenna elements  12 , while simultaneously outputting signals received from the low noise amplifiers  134  back to the power divider  132 . Of note, while reliance on a single power divider  132  may have particular application under certain circumstances, one skilled in the art should nonetheless appreciate that the functionality of the single power divider  132  shown in  FIG. 7  may be supplanted with a plurality of power dividers or other devices suited to apportion power and/or current. 
     What has been shown and described herein is a novel antenna system employing duplexers, power combiners/dividers, low power/noise amplifiers and/or other modules at or near the feeds of individual array antenna elements  12  in a manner that addresses shortcomings of the prior art. Benefits from such embodiments include minimization of filtering, cable and other equipment used in comparable systems. Embodiments of the present invention further mitigate the occurrence and effects of insertion loss attributable to power dividers and cabling in known antenna systems. Cumulative improvements realized by the disclosed embodiments may additionally realize signal improvements in system signal-to-noise ratio. System reliability is also improved by virtue of the low noise amplifiers  48  and duplexers  32  being distributed among multiple antenna elements  12 . Thus, the amplification system  30  can withstand one or more low noise amplifier  48  failures with minimal impact to signal quality. 
     While the present invention has been illustrated by a description of various embodiments, and while these embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative example shown and described. Accordingly, departures may be made from such details without departing from the spirit or scope of applicant&#39;s general inventive concept.