Abstract:
A distributed antenna array comprising a plurality of antenna elements, and a plurality of power amplifiers, each power amplifier being operatively coupled with one of said antenna elements and mounted closely adjacent to the associated antenna element, such that no appreciable power loss occurs between the power amplifier and the associated antenna element, each said power amplifier comprising a relatively low power, linear power amplifier.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims the filing benefit of Provisional Application U.S. Serial No. 60/244,881, filed Nov. 1, 2000, entitled “Integrated Active Antenna For Multi-Carrier Applications”, and is a continuation-in-part of U.S. patent application, Ser. No. 09/299,850, filed Apr. 26, 1999, entitled “Antenna Structure and Installation”, each disclosure of which is hereby incorporated herein by reference in its entirety. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention is directed generally to active antennas and more particularly to an integrated active antenna for multi-carrier applications.  
         BACKGROUND OF THE INVENTION  
         [0003]    In communications equipment such as cellular and Personal Communications Service (PCS), as well as multi-channel multi-point distribution systems (MMDS) and local multi-point distribution systems (LMDS), it has been conventional to receive and retransmit signals from users or 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 users or subscribers which may also utilize various forms of antennas and transceivers.  
           [0004]    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, with relatively long coaxial cables connecting with antenna elements mounted on the tower. The power losses experienced in the cables may necessitate some increases in the power amplification which is typically provided at the ground level infrastructure or base station, thus further increasing the expense per unit or cost per watt.  
           [0005]    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 (EIRP). 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 wafts. 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 combiners must be used.  
           [0006]    All of this additional circuitry to achieve linearity of the overall system, which is required for relatively high output systems, results in a relatively high cost per unit/watt.  
           [0007]    The present invention proposes placing linear amplifiers in the tower close to the antenna(s) and also, distributing the power across multiple antenna (array) elements, to achieve a lower power level per antenna element and utilize power amplifier technology at a much lower cost level (per unit/per watt).  
           [0008]    In accordance with one aspect of the invention, linear (multi-carrier) power amplifiers of relatively low power are utilized. In order to utilize such relatively low power amplifiers, the present invention proposes use of an antenna array in which one relatively low power linear amplifier is utilized in connection with each antenna element of the array to achieve the desired overall output power of the array.  
           [0009]    Moreover, the invention proposes installing a linear power amplifier of this type at or near the feed point of each element of a multi-element antenna array. Thus, the output power of the antenna system as a whole may be multiplied by the number of elements utilized in the array while maintaining linearity.  
           [0010]    Furthermore, the present invention does not require relatively expensive high power combiners, since the signals are combined in free space (at the far field) at the remote or terminal location via electromagnetic waves. Thus, the proposed system uses low power combining, avoiding otherwise conventional combining costs. Also, in tower applications, the system of the invention eliminates the power loss problems associated with the relatively long cable which conventionally connects the amplifiers in the base station equipment with the tower-mounted antenna equipment, i.e., by eliminating the usual concerns with power loss in the cable and contributing to a lesser power requirement at the antenna elements. Thus, by placing the amplifiers close to the antenna elements, amplification is accomplished after cable or other transmission line losses usually experienced in such systems. This may further decrease the need for low loss cables, thus further reducing overall system costs.  
           [0011]    The use of multi-carrier linear power amplifiers at or near the feed point of each element in the multi-element antenna array improves transmit efficiency, receive sensitivity and reliability for multi-carrier communications systems. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    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 invention.  
         [0013]    [0013]FIG. 1 is a simplified schematic of an antenna array utilizing linear power amplifier modules in accordance with one form of the invention;  
         [0014]    [0014]FIG. 2 is a schematic similar to FIG. 1 in showing an alternate embodiment;  
         [0015]    [0015]FIG. 3 is a block diagram of an antenna assembly or system in accordance with one aspect of the invention;  
         [0016]    [0016]FIG. 4 is a block diagram of a communications system base station utilizing a tower or other support structure, and employing an antenna system in accordance with one aspect of the invention;  
         [0017]    [0017]FIG. 5 is a block diagram of a communications system base station employing the antenna system in accordance with another aspect of the invention;  
         [0018]    [0018]FIG. 6 is a block diagram of a communications system base station employing the antenna system in accordance with yet another aspect of the invention;  
         [0019]    [0019]FIG. 7 and  8  are block diagrams of two types of communications system base stations utilizing the antenna system in accordance with still yet another aspect of the invention; and  
         [0020]    [0020]FIG. 9 is a simplified schematic of one form of linear amplifier, which may be used in connection with the invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0021]    Referring now to the drawings, and initially to FIGS. 1 and 2, there are shown two examples of a multiple antenna element antenna array  10 ,  10   a  in accordance with the invention. The antenna array  10 ,  10   a  of FIGS. 1 and 2 differ in the configuration of the feed structure utilized, FIG. 1 illustrating a parallel corporate feed structure and FIG. 2 illustrating a series corporate feed structure. In other respects, the two antenna arrays  10 ,  10   a  are substantially identical. Each of the arrays  10 ,  10   a  includes a plurality of antenna elements  12 , which may comprise monopole, dipole or microstrip/patch antenna elements. Other types of antenna elements may be utilized to form the arrays  10 ,  10   a  without departing from the invention.  
         [0022]    In accordance with one aspect of the invention, a multi-carrier, linear amplifier  14  is operatively coupled to the feed of each antenna element  12  and is mounted in close proximity to the associated antenna element  12 . In one embodiment, the amplifiers  14  are mounted sufficiently close to each antenna element so that no appreciable losses will occur between the amplifier output and the input of the antenna element, as might be the case if the amplifiers were coupled to the antenna elements by a length of cable or the like. For example, the power amplifiers  14  may be located at or near the feed point of each antenna element.  
         [0023]    In the antenna arrays of FIGS. 1 and 2, array phasing may be adjusted by varying the line length in the corporate feed or by electronic circuitry within the power amplifiers  14 . The array amplitude coefficient adjustment may be accomplished through the use of attenuators before or within the power amplifiers  14 , as shown in FIG. 3.  
         [0024]    Referring now to FIG. 3, an antenna system in accordance with the invention and utilizing an antenna array of the type shown in either FIG. 1 or FIG. 2 is designated generally by the reference numeral  20 . The antenna system  20  includes a plurality of antenna elements  12  and associated multi-carrier linear power amplifiers  14  as described above in connection with FIGS. 1 and 2. Also operatively coupled in series circuit with the power amplifiers  14  are suitable attenuator circuits  22 . The attenuator circuits  22  may be interposed either before or within the power amplifier  14 ; however, FIG. 3 illustrates them at the input to each power amplifier  14 . A power splitter and phasing network  24  feeds all of the power amplifiers  14  and their associated series connected attenuator circuits  22 . An RF input  26  feeds into this power splitter and phasing network  24 .  
         [0025]    Referring to FIG. 4, an antenna system installation utilizing the antenna system  20  of FIG. 3 is designated generally by the reference numeral  40 . FIG. 4 illustrates a base station or infrastructure configuration for a communications system such as a cellular system, a personal communications system PCS or a multi-channel multipoint distribution system (MMDS). The antenna structure or assembly  20  of FIG. 3 is mounted at the top of a tower or other support structure  42 . A DC bias tee  44  separates signals received via a coaxial cable  46  into DC power and RF components, and conversely receives incoming RF signals from the antenna system  20  and delivers the same to the coaxial line or cable  46  which couples the tower-mounted components to ground based components. The ground-based components may include a DC power supply  48  and an RF input/output  50  from a transmitter/receiver (not shown), which may be located at a remote equipment location, and hence is not shown in FIG. 4. A similar DC bias  52  receives the DC supply and RF input and couples them to the coaxial line  46 , and conversely delivers signals from the antenna structure  20  to the RF input/output  50 .  
         [0026]    [0026]FIG. 5 illustrates a communications system base station employing the antenna structure or system  20  as described above. In similar fashion to the installation of FIG. 4, the installation of FIG. 5 mounts the antenna system  20  atop a tower/support structure  42 . Also, a coaxial cable  46 , for example, an RF coaxial cable for carrying RF transmissions, runs between the top of the tower/support structure and ground based equipment. The ground based equipment may include an RF transceiver  60  which has an RF input from a transmitter. Another similar RF transceiver  62  is located at the top of the tower and exchanges RF signals with an antenna structure or system  20 . A power supply such as a DC supply  48  is also provided for the antenna system  20 , and is located at the top of the tower  42  in the embodiment shown in FIG. 5.  
         [0027]    Alternatively, the two transceivers  60 ,  62  may be RF-to-fiber optic transceivers (as shown for example, in FIG. 8), and the cable  46  may be a fiber optic or “optical fiber” cable, e.g., as shown in FIG. 8.  
         [0028]    [0028]FIG. 6 illustrates a communications system base station which also mounts an antenna structure or system  20  of the type described above at the top of a tower/support structure  42 . In similar fashion to the installation of FIG. 5, an RF transceiver and power supply such as a DC supply  48  are also located at the top of the tower/support and are operatively coupled with the antenna system  20 . A second or remote RF transceiver  60  may be located adjacent the base of the tower or otherwise within a range of a wireless link which links the transceivers  60  and  62 , by use of respective transceiver antenna elements  64  and  66  as illustrated in FIG. 6.  
         [0029]    [0029]FIGS. 7 and 8 illustrate examples of use of the antenna structure or system  20  of the invention in connection with communications system base stations, such as in-building communication applications by way of example. In FIG. 7, respective DC bias tees  70  and  72  are linked by an RF coaxial cable  74 . The DC bias tee  70  is located adjacent the antenna system  20  and has respective RF and DC lines operatively coupled therewith. The second DC bias tee  72  is coupled to an RF input/output from a transmitter/receiver and to a suitable DC supply  48 . The DC bias tees and DC supply operate in conjunction with the antenna system  20  and a remote transmitter/receiver (not shown) in much the same fashion as described hereinabove with reference to the system of FIG. 4.  
         [0030]    In FIG. 8, the antenna system  20  receives an RF line from a fiber-RF transceiver  80 , which is coupled through an optical fiber cable  82  to a second RF-fiber transceiver  84  which may be located remotely from the antenna and first transceiver  80 . A DC supply or other power supply for the antenna may be located either remotely, as illustrated in FIG. 8 or adjacent the antenna system  20 , if desired. The DC supply  48  is provided with a separate line operatively coupled to the antenna system  20 , in much the same fashion as illustrated, for example, in the installation of FIG. 6.  
         [0031]    [0031]FIG. 9 shows an example of a linear (multi-carrier) amplifier, which may be used as the amplifier  14 . The amplifier in FIG. 9 is a feed forward design; however, other forms of linear (multi-carrier) amplifiers may be used without departing from the invention.  
         [0032]    In one embodiment of the present invention, each of the amplifiers  14  has an input  86  operatively coupled to an RF transmitter/receiver (not shown) and an output  88  operatively coupled to the feed of each antenna element  12 . The multi-carrier linear power amplifier  14  is designed to reduce or eliminate the distortion created by amplification of the feed signal in the feed forward amplifier  14 .  
         [0033]    To this end, the amplifier  14  has a power splitter  90  that directs the feed signal transmitted by the RF transmitter/receiver (not shown) to a main amplifier  92  and to an input  94  of a carrier cancellation node  96  through a delay  98 . The main amplifier  92  receives the feed signal at an input  100  and generates a signal at its output  102  that comprises the feed signal amplified by a predetermined gain and distortion caused by amplification of the feed signal. The output signal generated by the main amplifier  92  is applied to a coupler  104  that directs the output signal of the main amplifier  92  to an attenuator  106  and to an input  108  of a distortion cancellation node  110  through a delay  112 .  
         [0034]    The attenuator  106  attenuates the output signal generated by the main amplifier  92  and applies the attenuated signal to a second input  114  of the carrier cancellation node  96 . The carrier cancellation node  96  utilizes the signals received at inputs  94  and  114  to remove the carrier signal from the attenuated signal applied by the attenuator  106  and generate a distortion signal at its output  116  that is applied to input  118  of an error amplifier  120 .  
         [0035]    The error amplifier  120  amplifies the distortion signal generated by the carrier cancellation node  96  and applies the amplified distortion signal to a second input  122  of the distortion cancellation node  110 . The distortion cancellation node  1   10  utilizes the signals received at inputs  108  and  122  to remove the distortion in the amplified feed signal applied by the main amplifier  92  and generate an essentially distortion-free amplified feed signal at its output  88  that is applied to the feed of an antenna element  12 .  
         [0036]    What has been shown and described herein is a novel antenna array employing power amplifiers or modules at or near the feeds of individual array antenna elements, and a number of novel installations utilizing such an antenna system.  
         [0037]    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 applicants&#39;general inventive concept.