Abstract:
Methods and apparatus are provided for a cellular communication system including superconducting components. More particularly, the inventions of this system include a tower mounted transmitter/receiver system having one or more antenna disposed atop a tower. The system includes a receive side subsystem having at least one superconducting component, such as an HTS filter. The system further includes a transmit side subsystem having an amplifier, preferably a power amplifier. The receive side subsystem and the transmit side subsystem are both disposed atop the tower substantially adjacent the antenna. Duplexed and multiplexed systems may be utilized. One or more connections may be provided between the tower mounted transmitter/receiver system and the ground or base station.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    The present application claims priority under 35 U.S.C. §119(e) from co-pending U.S. Provisional Application Serial No. 60/277,418, entitled “Apparatus and methods for improved tower mount systems for cellular communications,” filed Mar. 19, 2001, and from co-pending U.S. Provisional Application Serial No. 60/277,419, entitled “Method and apparatus for combined receive and transmit subsystems in cellular communication systems,” filed Mar. 19, 2001, the disclosures of which are expressly incorporated herein by reference in their entireties. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates generally to the field of telecommunications and cellular communications, such as, e.g., cellular telephone communications. More particularly, this invention relates to telecommunications and cellular communications systems that may include the use of tower mountable superconducting components, such as superconducting filter receiver systems, power amplified transmitter systems, and related enclosures.  
         BACKGROUND  
         [0003]    Radio frequency (RF) equipment have used a variety of approaches and structures for receiving and transmitting radio waves and other signals in selected frequency bands. The type of filtering structure used often depends upon the intended use and the specifications for the radio equipment. For example, dielectric filters may be used for filtering electromagnetic energy in the ultra-high frequency (UHF) band, such as, e.g., those used for cellular communications in the 800+ MHz frequency range. Because of an increase in the number of users utilizing a limited bandwidth, demand has increased for greater frequency selectivity than can be provided by normal or non-superconducting resonator filters, especially for RF signals in the ultra-high frequency bands that may be used for cellular communications. As a result, substantial attention has recently been devoted to the development of high temperature superconducting (HTS) RF filters for use in, for example, cellular telecommunications systems, to accomplish and optimize high frequency selectivity.  
           [0004]    HTS RF filters, or HTS front-end filters, may, however, be susceptible to failure or degradation in performance. For example, HTS front-end filters may fail when exposed to lightning surges or other high power signals. Furthermore, such filters are extremely temperature sensitive. For example, the use of such filters within tower mounted communications systems can raise significant heat management issues. One such issue is temperature regulation of a cold finger in a cryocooler used with an HTS filter system. U.S. Pat. No. 6,098,409, entitled “Temperature control of high temperature superconducting thin film filter subsystems,” and U.S. Pat. No. 6,256,999, also entitled “Temperature control of high temperature superconducting thin film filter subsystems,” address the issue of temperature regulation of a cold finger in a cryocooler. The disclosures of the &#39;409 and the &#39;999 patents are expressly and fully incorporated by reference herein. Another equally important issue is heat dissipation. Stated somewhat differently, for an HTS filter system to function properly, the heat of compression generated by a cryocooler incorporated within the system must be efficiently and reliably rejected to the ambient environment. If that heat generated by the cryocooler cannot be efficiently and reliably rejected, it may have a serious impact upon system operation. Depending upon the circumstances, insufficient heat dissipation into the ambient environment could result in inefficient cryocooler operation and/or cryocooler shut down. U.S. Pat. No. 6,311,498, entitled “Tower mountable cryocooler and HTSC filter system,” addresses one method of dealing with heat dissipation in HTS filter systems. The disclosure of the &#39;498 is expressly and fully incorporated herein by reference.  
           [0005]    Current tower mounted communications systems may include a receive side subsystem, such as an HTS filter system, mounted on the mast or tower. The transmit side subsystem, such as a power amplified transmitter, in comparison, is typically housed in a base station at the bottom of the tower. Those of ordinary skill in the art have been reluctant to mount transmit side subsystems at an elevated point on the tower. This reluctance on the part of those of ordinary skill in the art may be partly attributed to liability concerns regarding injuries to passersby that may be inflicted as a result of falling transmit side subsystems. In current tower mounted systems, a cable must be extended, or run, from a transmit side subsystem, typically located within the base station, to the antenna or antennas at an elevated point on the tower. The length of cable required, which will vary depending on the height of the tower, the elevation of the antennas, and the distance of the base station from the antenna, inevitably results in some signal loss. Accordingly, current transmit side subsystems must generate an adequate amount of power from the power amplified transmitter to overcome any signal loss due to the cable that must be run between the transmit side subsystem and the elevated antenna. These power amplified transmit side subsystems must therefore be able to generate a large amount of power, and, as a result, consume a large amount of energy. In addition to requiring a great deal of energy to operate, the placement of these power amplified transmit side subsystems in the base station generates a significant amount of heat within the base station itself, thereby requiring enhanced environmental cooling systems within the base station. The use of these enhanced cooling systems within the base station also increases the amount of energy required to operate the tower mounted telecommunications system.  
           [0006]    Thus, those of ordinary skill in the art would find an improved tower mounted communications system that reduces the cable run between the transmit side subsystem and the elevated antenna or antennas to be quite useful. It is also believed that those skilled in the art would find a tower mounted communications that may be operable with a less powerful amplified transmitter, compared to those currently used in known tower mounted systems, to be useful. Those skilled in the art would also find a communications system with remote units near the users to be useful.  
         SUMMARY OF THE INVENTION  
         [0007]    The present invention is directed to methods and systems for transmitting and receiving telecommunications signals. More particularly, the present invention is directed to tower mountable transmitter/receiver systems that incorporate superconducting materials. The systems of the present invention are optimized for transmitting and receiving telecommunications signals.  
           [0008]    In one aspect of the present invention, a tower mounted transmitter/receiver system is provided. The system may include a transmit antenna and a receive antenna disposed on a tower. The system may also have a transmit side subsystem with a powered amplifier that is disposed atop the tower and in communication with the transmit antenna. Additionally, a receive side subsystem disposed atop the tower and in communication with the receive antenna may be incorporated into the system. The receive side subsystem preferably incorporates an HTS filter. Also, the system may include a transmission path extending between a base station located at a base of the tower and the transmit and receive side subsystems.  
           [0009]    The transmit and receive antennas of this system may be incorporated into a single combined transmit/receive antenna. In this embodiment, the system further comprises a first duplexer coupled to the combined antenna, the transmit side subsystem, and the receive side subsystem. This first duplexer is preferably configured to provide a transmit signal to the combined antenna from the transmit side subsystem, and to provide a receive signal to the receive side subsystem from the combined antenna. The system may also incorporate a second duplexer coupled to the transmit side subsystem, the receive side subsystem, and the transmission path. Here, the second duplexer is preferably configured to provide a transmit signal to the transmit side subsystem, and to send a receive signal to the base station via the transmission path. Additionally, the system may include receive electronics disposed within the base station, transmit electronics disposed within the base station, and a third duplexer coupled to the transmission path, the receive electronics and the transmit electronics. The third duplexer may be configured to provide a receive signal to the receive electronics relayed from the second duplexer via the transmission path, and to send a transmit signal from the transmit electronics to the second duplexer via the transmission path.  
           [0010]    The system may include a power distribution unit. The power distribution unit may be coupled to the receive electronics and the transmit electronics. The power distribution unit is preferably configured to balance a strength of a transmit signal generated by the transmit electronics with a strength of a receive signal received by the receive electronics. In one embodiment, the receive electronics, the transmit electronics, and the power distribution unit all may be disposed within the base station.  
           [0011]    The transmit side subsystem of the system may include a RF filter that is in communication with the power amplifier and the transmit antenna. Additionally, the receive side subsystem may include a cryocooler, a cryogenic enclosure in thermal communication with the cryocooler, and a low noise amplifier coupled to the HTS filter. The HTS filter and the low noise amplifier may be disposed within the cryogenic enclosure.  
           [0012]    In another embodiment, the transmit side subsystem may include a signal combiner, a plurality of power amplifiers coupled to the signal combiner, and a RF transmitter filter coupled to the signal combiner. The signal combiner preferably receives a plurality of transmitted signals from the plurality of power amplifiers, combines the plurality of transmitted signals into a single transmitted signal, and relays the transmitted signal to the RF transmitter filter.  
           [0013]    In another aspect of the present invention, another tower mounted transmitter/receiver system is provided. The system may includes an antenna that is disposed atop a tower. The antenna is preferably configured to both receive and transmit RF signals. A transmit side subsystem disposed atop the tower may also be included in the system. The transmit side subsystem may be in communication with the antenna, and may include a powered amplifier. The system may also incorporate a receive side subsystem disposed atop the tower and in communication with the antenna. This receive side subsystem may include an HTS filter. Receive electronics in communication with the receive side subsystem may be provided. Similarly, transmit electronics that are in communication with the transmit side subsystem may also be provided with this system.  
           [0014]    In one embodiment of this system, the receive side subsystem further includes a cryocooler, a cryogenic enclosure in thermal communication with the cryocooler, a cold stage within the cryogenic enclosure, and a low noise amplifier coupled to the HTS filter. Preferably, the HTS filter and the low noise amplifier are located within the cryogenic enclosure, and are disposed upon the cold stage. Also, the transmit side subsystem may further comprise a RF transmitter filter coupled to the power amplifier. The RF transmitter filter is preferably configured to relay transmitted signals from the power amplifier to the antenna.  
           [0015]    The system may further include a plurality of duplexers. For example, the system may include a first duplexer coupled to the receive electronics and the transmit electronics, a second duplexer coupled to the transmit side subsystem, the receive side subsystem, and the first duplexer, and a third duplexer coupled to the antenna, the transmit side subsystem, and the receive side subsystem. In this embodiment, the first duplexer is preferably configured to relay received signals from the second duplexer to the receive electronics and relay transmitted signals from the transmit electronics to the second duplexer. Additionally, the second duplexer is preferably configured to relay transmitted signals from the first duplexer to the transmit side subsystem and relay received signals from the receive side subsystem to the first duplexer. Also, the third duplexer is preferably configured to receive transmitted signals from the transmit side subsystem, relay the transmitted signals to the antenna, receive received signals from the antenna, and relay the received signals to the receive side subsystem. Furthermore, the first duplexer, the receive electronics, and the transmit electronics may all be disposed within a base station.  
           [0016]    In another aspect of the present invention, another tower mounted transmitter/receiver system is provided. The system may include an antenna configured to receive and transmit RF signals. A transmit side subsystem disposed atop the tower may be provided. The transmit side subsystem may be in communication with the antenna. The transmit side subsystem may also be configured to process digital signals. Additionally, a receive side subsystem disposed atop the tower may be provided. The receive side subsystem may be in communication with the antenna. As with the transmit side subsystem, the receive side subsystem may be configured to process digital signals. The system may also include a digital transmission path between a base station located at a base of the tower and the transmit and receive side subsystems. The antenna may comprise a transmit antenna in communication with the transmit side subsystem, as well as a receive antenna in communication with the receive side subsystem. Additionally, the digital transmission path may comprise a fiber optic cable.  
           [0017]    In one embodiment of this system of the present invention, the transmit side subsystem preferably includes a digital to analog converter coupled to the digital transmission path, an up-conversion unit coupled to the digital to analog converter, and a power amplifier coupled to the up-conversion unit and to the antenna. Here, the transmit side subsystem is preferably configured to convert a digital signal to an analog signal, and then deliver the analog signal to the antenna.  
           [0018]    In another embodiment of this system, the receive side subsystem may include an analog to digital converter coupled to the digital transmission path, a down-conversion unit coupled to the analog to digital converter, a low noise amplifier coupled to the down-conversion unit, and an HTS filter coupled to the low noise amplifier and the antenna. This receive side subsystem is preferably configured to receive an analog signal from the antenna, and then convert the analog signal to a digital signal. Furthermore, the receive side subsystem may include a cryocooler, a cryogenic enclosure in thermal communication with the cryocooler, and a cold stage within the cryogenic enclosure. The HTS filter and the low noise amplifier are preferably disposed on the cold stage. Additionally, the cryocooler may be a Stirling cryocooler.  
           [0019]    This system of the present invention may also include receive electronics coupled to the digital transmission path, the receive electronics being configured to process digital signals. Likewise, the system may include transmit electronics coupled to the digital transmission path, the transmit electronics also being configured to generate digital signals.  
           [0020]    Additionally, the system may include a plurality of multiplexers. For example, a first multiplexer may be provided that is coupled to the antenna, the transmit side subsystem and the receive side subsystem. Also, the system may include a second multiplexer that is coupled to the transmit side subsystem, the receive side subsystem, and the digital transmission path. Finally, this embodiment of the system may include a third multiplexer coupled to the digital transmission path, the receive electronics, and the transmit electronics. Preferably, the first multiplexer is configured to relay received signals from the antenna to the receive side subsystem and relay signals from the transmit side subsystem to the antenna. The second multiplexer is preferably configured to relay signals from the receive side subsystem to the digital transmission path and relay signals from the digital transmission path to the transmit side subsystem. The third multiplexer is preferably configured to relay signals from the digital transmission path to the receive electronics and relay signals from the transmit electronics to the digital transmission path. In one embodiment, the first, second, and third multiplexers are duplexers.  
           [0021]    In another embodiment of this system of the present invention, a power distribution unit is provided. The power distribution unit may be coupled to the receive and transmit electronics. The power distribution unit is preferably operable to balance a strength of a digital signal generated by the transmit electronics with a strength of a digital signal received by the receive electronics. In one alternative, the power distribution unit is disposed atop the tower. In another alternative, the power distribution unit is located within the base station. Similarly, both the receive electronics and the transmit electronics may be disposed in the base station.  
           [0022]    Other objects and features of the present invention will become apparent from consideration of the following description taken in conjunction with the accompanying drawings. 
       
    
    
     DESCRIPTION OF THE DRAWINGS  
       [0023]    [0023]FIG. 1 illustrates a first embodiment of a tower mounted transmitter/receiver system in accordance with the present invention.  
         [0024]    [0024]FIG. 2 illustrates a second embodiment of a tower mounted transmitter/receiver system in accordance with the present invention, wherein the system includes a combined transmit/receive antenna.  
         [0025]    [0025]FIG. 3 a  illustrates a third embodiment of a tower mounted transmitter/receiver system in accordance with the present invention, wherein the system includes a transmit side subsystem having a plurality of power amplifiers and a combiner.  
         [0026]    [0026]FIG. 3 b  illustrates a fourth embodiment of a tower mounted transmitter/receiver system in accordance with the present invention, wherein the system includes a plurality of multiplexers and a transmit side subsystem having a plurality of power amplifiers.  
         [0027]    [0027]FIG. 4 illustrates a fifth embodiment of a tower mounted transmitter/receiver system in accordance with the present invention, wherein the system is configured to generate and process digital signals.  
         [0028]    [0028]FIG. 5 illustrates an embodiment of a system in accordance with the present invention that includes a plurality of remote transmitter/receiver systems coupled to a main base station.  
         [0029]    [0029]FIG. 6 illustrates another embodiment of a system in accordance with the present invention that includes a plurality of remote transmitter/receiver systems coupled to a main base station.  
     
    
     DETAILED DESCRIPTION  
       [0030]    Turning now to the drawings, FIG. 1 illustrates a tower mounted telecommunications system  100  of the present invention. The system  100  includes a tower or mast  102  and a base station  150  located at the bottom of the tower  102 . An antenna or a plurality of antennas is mounted towards the top of the tower  102 . In the illustrated embodiment, a plurality of antennas, i.e., a transmit antenna  104  and a receive antenna  106 , is mounted at the top of the tower  102 . A transmit cable  105 , which is preferably a coaxial cable, connects the transmit antenna  104  with a transmit side subsystem  116  located within a transmitter/receiver system  110 . Similarly, a receive cable  107 , which is also preferably a coaxial cable, connects the receive antenna  106  with a receive side subsystem  120  located within the transmitter/receiver system  110 . The transmitter/receiver system  110  is mounted in close proximity to the antennas  104 ,  106  in order to minimize the cable length required to connect the antennas  104 ,  106  with the transmitter/receiver system  110 . A transmission line  132 , which is, like the transmit cable  105  and the receive cable  105 , preferably a coaxial cable, connects the transmitter/receiver system  110  with the base station  150 .  
         [0031]    The transmitter/receiver system  110  preferably includes an environmentally protective system housing  134 . The housing  134  contains the transmit side subsystem  116  and the receive side subsystem  120 , and is designed to isolate the transmitter/receiver system  110  from ambient forces. Any suitable housing that insulates the transmitter/receiver system  110  from external forces and inclement weather may be used for the housing  134 . The housing  134  may be mounted to the tower  102  using any suitable attachment means, such as, e.g., brackets, placement on a platform, being formed as an integral part of the tower  102 , or the like.  
         [0032]    As previously noted, the transmit side subsystem  116  is located within the housing  134 . Preferably, the transmit side subsystem  116  includes a transmitter filter  112  and a power amplifier  114 . In this embodiment of the system  100 , the transmitter filter  112  is a conventional, non-superconducting filter. The transmit cable  105  connects the transmit antenna  104  with the transmitter filter  112 . The transmitter filter  112 , in turn, is coupled to the power amplifier  114 .  
         [0033]    The receive side subsystem  120  is also located within the housing  134 . The receive side subsystem  120  is preferably an HTS-based RF front-end receiver that incorporates both an HTS filter  122  and a low noise amplifier  124  (LNA). Although one HTS filter  122  and one LNA  124  is shown in FIG. 1, a plurality of HTS filters  122  and a plurality of LNAs  124  may be incorporated into the receive side subsystem  120 . The receive side subsystem  120  further includes a cryocooler  126  that is used to cool the HTS filter  122  and LNA  124 , and possibly other electronic components that may be incorporated into the receive side subsystem  120 .  
         [0034]    The HTS filter  122  is preferably manufactured from a thin-film superconductor, although the present invention also contemplates other constructions such as thick-film superconductors. The thin-film superconductor may, for example, comprise a yttrium containing superconductor known generally as YBCO superconductors, or, alternatively, a thallium-based superconducting compound. U.S. Pat. No. 6,083,884, entitled, “A-axis high temperature superconducting films with preferential in-plane alignment,” and U.S. Pat. No. 5,358,926, entitled, “Epitaxial thin superconducting thallium-based copper oxide layers,” disclose exemplary thin-film superconductors that may be used with the present invention. The disclosures of the &#39;884 and the &#39;926 patents are fully and expressly incorporated by reference herein. The invention is not, however, limited to a particular type or class of superconductors, i.e., any HTS superconductor that will properly filter RF signals at HTS temperatures may be used in constructing the HTS filter  122 .  
         [0035]    The cryocooler  126  included within the receive side subsystem  120  may be any suitable cryocooler, such as, e.g., a Stirling cycle cryocooler, a Brayton cycle cryocooler, a Gifford-McMahon cryocooler, a pulse tube cryocooler, and the like. Exemplary cryocoolers are disclosed in U.S. Pat. No. 6,327,862, entitled, “Stirling cycle cryocooler with optimized cold end design,” and U.S. Pat. No. 6,141,971, entitled “Cryocooler motor with split return iron.” The disclosures of the &#39;862 and the &#39;971 patents are fully and expressly incorporated herein by reference. U.S. Pat. No. 6,311,498, entitled “Tower mountable cryocooler and HTSC filter system,” and which has already been incorporated by reference, also discusses cryocoolers suitable for use with the present invention.  
         [0036]    The cryocooler  126  is thermally coupled at its cold end to a cryogenic enclosure  128  that contains the HTS components and other electronics. The cryogenic enclosure  128  is preferably a vacuum dewar. The use of a vacuum dewar for the cryogenic enclosure  128  minimizes the transfer of heat from the external environment to the inside of the cryogenic enclosure  128 .  
         [0037]    A cold stage  127  is preferably located within the cryogenic enclosure  128 . The cold stage  127  preferably contains thereon the HTS filter  122  and the LNA  124 . Optionally, other electronic components that are used in the receive side subsystem  120  may also be located upon the cold stage  127 . The cold stage  127  may have a single face or a plurality of faces to hold a number of HTS filters  122  and LNAs  124 . A cooling transfer segment  125  couples the cold stage  127  with the cryocooler  126 . The cooling transfer segment  125  facilitates thermal transfer between the cold stage  127  and the cryocooler  126 .  
         [0038]    Further details of an exemplary receive side subsystem  120  suitable for use with the present invention are described in co-pending U.S. application Ser. No. 10/017,147, filed Dec. 13, 2001, and entitled, “MEMS-based bypass system for use with a HTS RF receiver,” which has been assigned to the assignee of the present invention. The specification of U.S. application Ser. No. 10/017,147 is fully and expressly incorporated by reference herein.  
         [0039]    A RF signal is received by the receive antenna  106  and transmitted to the receive side subsystem  120  via the receive cable  107 . Once received by the receive side subsystem  120 , the RF signal, i.e., the received signal, is filtered by the HTS filter  122 , and is amplified by the LNA  124 . In the embodiment of the system  100  shown in FIG. 1, the filtered and amplified RF signal is then relayed to a first transmitter/receiver system duplexer  130 .  
         [0040]    Referring again to the transmit side subsystem  116 , a RF signal is received by the power amplifier  114  from the first transmitter/receiver system duplexer  130 . The power amplifier  114  increases the signal strength of the RF signal to a desired level, and then relays the amplified RF signal to the transmitter filter  112 . The filtered, amplified RF signal is subsequently sent to the transmit antenna  104  via the transmit cable  105 . The transmit antenna  104  then broadcasts the filtered, amplified RF signal, i.e., the transmitted signal, to the area covered by the system  100 . In an alternative embodiment of system  100 , the transmitter filter  112  is located within the base station  150  rather than atop the tower  102 . In this alternative embodiment, a transmitted signal is filtered by the transmitter filter  112  prior to being amplified by the power amplifier  114 .  
         [0041]    As noted in the aforementioned discussion of the receive side subsystem  120  and the transmit side subsystem  116 , the transmitter/receiver system  110  includes the first transmitter/receiver system duplexer  130 . Use of the first transmitter/receiver system duplexer  130  enables the system  100  to carry both received and transmitted signals to and from the base station  150  using a single transmission line  132 . Use of a single transmission line  132  to travel and extend between the tower  102  and the base station  150  reduces the space required to operate the system  100 . The reduction of space through the use of a single transmission line  132  is of particular benefit in situations where an operator of the system  100  leases the space occupied by the system  100 , i.e., less space needs to be leased in order to run the transmission line  132 .  
         [0042]    When transmitting a signal, transmit electronics  156  in the base station  150  generate the transmit signal, and relays the transmit signal to a base station side duplexer  152 . As shown in FIG. 1, the base station side duplexer  152  may be disposed within the base station  150  itself. The base station side duplexer  152  combines the transmit signal into a combined signal that may include received signals, and the transmit signal is relayed via the transmission line  132  to the transmitter/receiver system  110 .  
         [0043]    In the transmitter/receiver system  100 , the first transmitter/receiver system duplexer  130  splits the transmit signal from the combined signal that includes both received and transmitted signals, and then relays the transmitted signal to the power amplifier  114 . When receiving a signal, the first transmitter/receiver system duplexer  130  combines a received signal with transmitted signals, and then relays the received signal, as a component of the combined signal, to the base station  150  via the transmission line  132 . In the base station  150 , the base station side duplexer  152  splits the received signal from the combined signal, and the received signal is provided to receive electronics  154  for processing.  
         [0044]    As illustrated in FIG. 1, the system  100  further includes a power distribution unit  158  coupled to both the receive electronics  154  and the transmit electronics  156 . The power distribution unit  158  is shown as being located within the base station  150 . Alternatively, the power distribution unit  158  may be mounted atop the tower  102 , in close proximity to the transmitter/receiver system  110 . The power distribution unit  158  optimizes the operation of the system  100  by determining the coverage range or radius of the receive side subsystem  120 , and then setting the power of the power amplifier  114  of the transmit side subsystem  116  to substantially match the coverage range or radius of the receive side subsystem  120 . In doing so, the power distribution unit  158  ensures that users within an area covered by the system  100  can both transmit and receive RF signals. In another embodiment of the power distribution unit  158 , the power distribution unit  158  merely provides a source of power to the transmit electronics  156 , and optionally also the receive electronics  154 .  
         [0045]    For either embodiment, a computer (not shown), such as, e.g., a personal computer, a notebook computer, a personal digital assistant, and the like, may be coupled to the power distribution unit  158  in order to diagnose any problems that may arise during the operation of the system  100 . Here, the computer is configured to download data regarding the power usage of the transmit electronics  156  and/or the receive electronics  154  from the power distribution unit  158 . Using the power usage data, the computer is able to determine any abnormal operation characteristics of either the transmit electronics  156  and/or the receive electronics  154 , thereby enabling the diagnosis and resolution of any problems by the operators of the system  100 .  
         [0046]    Turning now to FIG. 2, another system of the present invention, tower mounted system  200 , is illustrated. System  200  includes many of the same components as system  100 . For the sake of simplicity, the numbering of the common components of systems  100  and  200  will remain constant. Further, reference is made to the description of these common components in the earlier discussion of system  100 . For example, system  200  includes a tower  102  and a base station  150 , with the base station  150  containing at least receive electronics  154 , transmit electronics  156 , and, optionally, a power distribution unit  158 . The power distribution unit  158  may alternatively be located atop the tower  102  in close proximity to a transmitter/receiver system  210 . A base station side duplexer  152  may also be placed within the base station  150 . A transmission line  132  extends between the base station side duplexer  152  and the transmitter/receiver system  210 , and the base station side duplexer  152  is further coupled to the receive and transmit electronics  154 ,  156 . Also, as with system  100 , the base station side duplexer  152  may combine and split transmitted and received signals that are carried via the transmission line  132  between the transmitter/receiver system  210  and the receive and transmit electronics  154 ,  156  within the base station  150 .  
         [0047]    System  200  incorporates a combined transmit/receive antenna  203 . The transmit/receive antenna  203  may be any antenna capable of both transmitting signals and receiving signals in a single unit. The transmit/receive antenna  203  is coupled to the transmitter/receiver system  210  via a single transmit/receive cable  209 . Through the use of a single transmit/receive cable  209  between the antenna  203  and the transmitter/receiver system  210 , as well as a single transmission line  132  between the transmitter/receiver system  210  and the base station  150 , system  200  further reduces the space required for operation. This provides a benefit in cost savings if, for example, space must be leased for the cable runs.  
         [0048]    The transmitter/receiver system  210  contains a transmit side subsystem  116  and a receive side subsystem  120  that are substantially similar to the subsystems in system  100 , and reference is made to the description of these subsystems with regard to system  100  for further operational details.  
         [0049]    In addition to the components contained in the transmitter/receiver system  110  of system  100 , such as, e.g., the first transmitter/receiver system duplexer  130 , the transmitter/receiver system  210  of system  200  further incorporates a second transmitter/receiver system duplexer  230 . The second transmitter/receiver system duplexer  230  splits a received signal from the transmit/receive antenna  203  from a transmitted signal from the transmit side subsystem  116 , both of the transmitted and received signals being carried on the transmit/receive cable  209  as part of a combined signal, and relays the received signal to the receive signal subsystem  120  for processing. Also, the second transmitter/receiver system duplexer  230  combines the transmitted signals with the received signals in order to relay the transmitted signals to the transmit/receive antenna  203  via the transmit/receive cable  209 , as a component of a combined signal.  
         [0050]    As noted, the first transmitter/receiver system duplexer  130  is provided within the transmitter/receiver system  210  to combine received signals with transmitted signals in order to send the received signals, as part of a combined signal, to the base station  150 . Within the base station  150 , the base station side duplexer  152  splits the received signals from the combined signal, and then relays the received signals to the receive electronics  154 . The base station side duplexer  152  also receives transmitted signals from the transmit electronics  156 , combines the transmitted signals with received signals in order to send the transmitted signals, as part of a combined transmit/receive signal, to the transmitter/receiver system  210  via the transmission line  132 . Within the transmitter/receiver system  210 , the first transmitter/receiver system duplexer  130  splits the transmitted signals from the combined transmit/receive signal, and relays the transmitted signals to the transmit side subsystem  116  for further processing.  
         [0051]    [0051]FIG. 3 a  illustrates another embodiment of a system of the present invention, namely, tower mounted system  300 . System  300 , as with the other embodiments of the systems of the present invention, includes a transmitter/receiver system  310  and a base station  350 . Although not shown in FIG. 3 a , it should be appreciated that the transmitter/receiver system  310  is mounted atop a tower (not shown). System  300  includes components that are also used with the other systems of the present invention. Accordingly, for these common components, identical numbering is used for system  300 . Additionally, reference is made to the descriptions of the other systems, such as, e.g., system  100 , for the details of these common components.  
         [0052]    The transmitter/receiver system  310  of system  300  includes a transmit side subsystem  316  that incorporates a plurality of powered amplifiers  114   a ,  114   b ,  114   c , rather than a single powered amplifier, such as, e.g., in system  100 . Although three powered amplifiers  114   a - c  are illustrated in FIG. 3 a , a smaller or a greater number of powered amplifiers may be used. Each powered amplifier  114   a - c  receives a transmitted signal from a transmit electronics unit  156   a - c  located within base station  350 . Each powered amplifier  114   a - c  is coupled to a transmit electronics unit  156   a - c  via a transmission line  332   a - c , respectively. Preferably, a like number of transmit electronics units and powered amplifiers is used, i.e., in embodiments of-system  300  incorporating more than three powered amplifiers, an equivalent number of transmit electronics units is provided in the base station  350 . Alternatively, differing numbers of powered amplifiers and transmit electronics units may be used by incorporating multiplexers to combine signals in order to compensate for odd numbers of powered amplifiers and transmit electronics units. Turning back to the embodiment shown in FIG. 3 a , each transmit electronics unit  156   a - c  is further coupled to a power distribution unit  158 , and the power distribution unit  158  is also coupled to receive electronics  154 . Although illustrated as being within base station  350 , the power distribution unit  158  may alternatively be mounted atop the tower (not shown). The power distribution unit  158  is operable to balance the signal strengths of the transmitted signals with the signal strengths of received signals received by the receive antenna  106 , and processed by the receive side subsystem  120  and receive electronics  154 . Here, the receive side subsystem  120  and receive electronics  154  are coupled via a reception line  332   d.    
         [0053]    The transmit side subsystem  316  further includes a signal combiner  360  coupled to the powered amplifiers  114   ac , as well as a transmitter filter  112 . The signal combiner  360  combines the amplified, transmitted signals sent by the powered amplifiers  114   a - c  into a single combined transmitted signal, and then relays the combined transmitted signal to the transmitter filter  112 . The combined transmitted signal is subsequently sent to the transmit antenna  104  for broadcast to the area covered by the system  300 .  
         [0054]    An alternative embodiment of system  300 , system  300 ( i ), is illustrated in FIG. 3 b . System  300 ( i ) incorporates a single combined transmit/receive antenna  203 , which has been discussed with respect to system  200 , in lieu of the separate transmit antenna  104  and receive antenna  106  of system  300 .  
         [0055]    Multiplexers  372 ,  374 , and  376  are also included in system  300 ( i ). A first multiplexer  374  is provided within the transmitter/receiver system  310 ( i ). The first multiplexer  374  provides transmitted signals to the power amplifiers  114   a - c , and also receives a received signal from the receive side subsystem  120  and relays the received signal to the base station  350 ( i ) via transmission line  332 ( i ). only a single transmission line  332 ( i ) is required to transmit signals between the transmitter/receiver system  310 ( i ) and the base station  350 ( i ) since the multiplexers  372 ,  374 , and  376  are configured to process combined transmit/receive signals, similar to the duplexers discussed with respect to other embodiments of the present invention.  
         [0056]    The transmitted signals provided to the power amplifiers  114   a - c  by the first multiplexer  374  are processed in a substantially similar manner as the processing of transmitted signals in system  300 . With system  300 ( i ), however, the filtered, combined transmitted signal is processed by a second multiplexer  372 , i.e., combined with received signals to form a combined transmit/receive signal, prior to being sent to the combined antenna  203  via the transmit/receive cable  209 . The transmitted signal is then broadcast to the coverage area by the combined antenna  203 .  
         [0057]    The combined antenna  203  receives RF signals from the coverage area, and relays the received signals, as a component of a combined transmit/receive signal, to the second multiplexer  372 . The second multiplexer  372  provides the received signals to the receive side subsystem  120  for processing. The received signals are then provided to the first multiplexer  374 , which transmits the received signals to a base station side multiplexer  376  via a transmission line  332 ( i ) as part of a combined transmit/receive signal. The base station side multiplexer  376  is operable for splitting received signals from a combined transmit/receive signal, and providing received signals to receive electronics  154 . The base station side multiplexer  376  is also capable of receiving transmitted signals from transmit electronics  156   a - c , combining those signals with received signals, and relaying the transmitted signals, as part of the combined signal, to the first multiplexer  374 . As illustrated, the base station side multiplexer  376  is disposed within base station  350 ( i ).  
         [0058]    Turning now to FIG. 4, another embodiment of the present invention, tower mounted system  400 , is illustrated. System  400  includes many of the same components that are also included in other embodiments of the systems of the present invention, such as, e.g., system  200  that is illustrated in FIG. 2. Therefore, common components of systems  200  and  400  are identified by the same numbers. Additionally, reference is made to the description of these components with regard to system  200 , as these components operate substantially the same in system  400 .  
         [0059]    System  400  incorporates a digital fiber transmission line  432 , which may be, e.g., a fiber optic cable, that enables the system  400  to transmit and receive digital signals. Digital transmission signals are sent to a transmitter/receiver system  410  from a base station  150  via the digital fiber transmission line  432 . In a similar fashion, digital received signals are sent to a base station  450  from the transmitter/receiver system  410  via the digital fiber transmission line  432 . As with the other embodiments of the present invention, the transmitter/receiver system  410  is preferably mounted atop a tower (not shown). Because a single digital transmission line  432  is used to carry digital signals between the transmitter/receiver system  410  and the base station  450 , a base station side duplexer  152  is provided in the base station  150  to split the transmitted and received signals from a combined signal. Also, a first transmitter/receiver duplexer  130  is provided in the transmitter/receiver system  410  to combine the received signals with the transmitted signals into a combined signal prior to the transmitter/receiver system  410  sending the received signal, which is within the combined signal, to the base station  450  via the digital transmission line  432 . In a similar fashion, the first transmitter/receiver duplexer  130  splits a transmitted signal from the combined signal prior to relaying the transmitted signal to the transmit side subsystem  416 .  
         [0060]    Turning to the transmit side subsystem  416 , the subsystem  416  includes a digital to analog converter (DAC)  474  that receives a digital transmitted signal from the first transmitter/receiver system duplexer  130 . The DAC  474  converts the digital transmitted signal to an analog signal. An up-conversion unit  476  then processes the analog transmitted signal to suppress any distortion introduced by the DAC  474 . The up-conversion unit  476  includes at least one mixer and one filter, and may include a plurality of mixers and filters. To process a signal, the up-conversion unit  476  receives an analog transmitted signal that is at a base frequency. A mixer of the up-conversion unit  476  is utilized to increase the frequency of the analog transmitted signal to an intermediate frequency. A filter of the up-conversion unit  476  is then utilized to eliminate any extraneous noise and distortion introduced by increasing the analog transmitted signal to the intermediate frequency. The up-conversion unit  476  may be operated to increase the frequency of the analog transmitted signal to a plurality of intermediate frequencies. Finally, a mixer of the up-. conversion unit  476  is used to increase the analog transmitted signal from an intermediate frequency to an operating frequency, and a filter of the up-conversion unit  476  is used to eliminate extraneous noise and distortion that may be introduced by increasing the analog transmitted signal to the operating frequency.  
         [0061]    The processed analog transmitted signal is then amplified by the power amplifier  114 , which relays the amplified signal to a RF filter  112 . The transmitted signal is combined by a second transmitter/receiver system duplexer  230  into a combined signal with received signals, and the transmitted signal, as part of a combined signal, is relayed to a transmit/receive antenna  203 , via a transmission line  209 , for broadcast into the area covered by the system  400 .  
         [0062]    The transmit/receive antenna  203  receives signals from the coverage area and relays the received signals to the second transmitter/receiver system duplexer  230  as part of a combined signal that includes transmit signals. Here, the transmit/receive antenna  203  receives analog signals. The second transmitter/receiver system duplexer  230  separates the received signals from the combined signal, and sends the received signals to a cryogenically cooled receive side subsystem  420 , which includes similar cryogenically cooled components as the other receive side subsystems of the present invention, such as, e.g., receive side subsystem  120 . Regarding the processing of the received signals by the cryogenically cooled portions of the receive side subsystem  420 , reference is made to the discussion of the receive side subsystem  120  elsewhere in this specification. The receive side subsystem  420  further includes a down-conversion unit  472  to condition the analog received signals prior to processing by an analog-to-digital converter (ADC)  470 . Similar to the up-conversion unit  476 , the down-conversion unit  472  includes at least one mixer and one filter, and may include a plurality of mixers and filters. To process a signal, the down-conversion unit  472  receives an analog received signal that is at an operating frequency. A mixer of the down-conversion unit  472  is utilized to decrease the frequency of the analog received signal to an intermediate frequency. A filter of the down-conversion unit  472  is then utilized to eliminate any extraneous noise and distortion introduced by decreasing the analog received signal to the intermediate frequency. Like the up-conversion unit  476 , the down-conversion unit  472  may be operated to decrease the frequency of the analog received signal to a plurality of intermediate frequencies. Finally, a mixer of the down-conversion unit  472  is used to decrease the analog received signal from an intermediate frequency to a base frequency. A filter of the down-conversion unit  472  is then used to eliminate extraneous noise and distortion that may be introduced by decreasing the analog received signal to the operating frequency.  
         [0063]    The ADC  470  converts the processed analog received signals to digital received signals, and then the first transmitter/receiver system duplexer  130  combines the received signals with transmitted signals, and the combined signal is sent to the base station  450  for further processing via the digital fiber transmission line  432 . Receive electronics  454  and transmit electronics  456  that are capable of processing digital signals are provided within the base station  450 . Additionally, a power distribution unit  158  may also provided within the base station  450  in order to equalize the signal strengths of the transmitted signals relative to the received signals. Alternatively, the power distribution unit  158  may be mounted atop the tower (not shown).  
         [0064]    In an alternative embodiment of system  400 , separate transmit and receive antennas (not shown) are used rather than a single transmit/receive antenna  203 . In this alternative embodiment, the second transmitter/receiver system duplexer  230  is not provided since there is no need to combine signals prior to sending a transmit signal to the transmit antenna, nor is there a need to split a receive signal, from a combined signal, received from the receive antenna prior to further processing by the receive side subsystem  420 .  
         [0065]    In a further alternative embodiment of the system  400 , the antenna of the system, which may be the combined antenna  203  or discrete transmit and receive antennas, is configured to digitally transmit and receive signals. With this embodiment, the need to convert digital signals to analog, and vice versa, is eliminated. Consequently, this alternative embodiment of system  400  does not include the DAC  474  and up-conversion unit  476  within the transmit side subsystem  416 . Furthermore, this system does not include the ADC  470  and the down-conversion unit  472  in the receive side subsystem  420 . These components are unnecessary in this alternative embodiment of system  400  because this system does not transmit or receive analog signals, but, rather, transmits and receives digital signals exclusively.  
         [0066]    For any of the systems of the present invention, a switched bypass unit (not shown) may be incorporated into the transmitter/receiver systems. In the event of an electrical surge in a receive path of the systems, a switched bypass unit located within the receive side subsystems directs the receive signals around the HTS filters. Also included in the switched bypass unit may be one or more LNAs, which may or may not be cooled, along with any other circuitry in the path of the receive signals that may be considered prone to failure. A switched bypass unit may also be provided in the transmit side subsystem to allow the subsystem to operate notwithstanding a catastrophic failure of any of the components of a transmit side subsystem of a system of the present invention. A suitable switched bypass unit is disclosed in co-pending U.S. application Ser. No. 10/017,147, entitled, “MEMS-based bypass system for use with a HTS RF receiver,” which has already been fully and expressly incorporated by reference herein.  
         [0067]    Other alternative embodiments of the systems of the present invention disclosed herein may incorporate more than two antennas. In these alternative embodiments, suitable multiplexers are incorporated into the systems. For example, in embodiments of the system that include three antennas, triplexers are incorporated within the transmitter/receiver systems and the base stations. Similarly, in embodiments of the system that include four antennas, quadplexers are included in the transmitter/receiver systems and in the base stations. Accordingly, in embodiments of the system with more than two antennas, multiplexers that are suitable for processing the number of signal paths generated by the number of antennas are included.  
         [0068]    Turning now to FIG. 5, FIG. 5 illustrates a system  500  according to the present invention that includes a plurality of transmitter/receiver systems  410 ( 1  to n) installed at a plurality of locations in a coverage area. Like system  400  shown in FIG. 4, system  500  is configured to transmit and receive digital signals. The illustrated embodiment of system  500  includes eight transmitter/receiver systems  410 , which are identified as  410 ( 1 ) to  410 ( 8 ). It will be appreciated, however, that either a greater number or smaller number of transmitter/receiver systems  410  may be included with system  500 .  
         [0069]    The plurality of transmitter/receiver systems  410 ( 1  to  8 ) are coupled to a main base station  550 . Each transmitter/receiver system  410 ( 1  to  8 ) is also preferably coupled to a corresponding combined transmit/receive antenna  203 ( 1  to  8 ).  
         [0070]    System  500  is not limited to tower mounted installations. Rather, each transmitter/receiver system  410 ( 1  to  8 ) is mountable at various locations within the coverage area, and at locations within the coverage area that are remote from the main base station  550 . Moreover, each transmitter/receiver system  410 ( 1  to  8 ) is preferably located in proximity to the users of the system. Exemplary locations for placement of a transmitter/receiver system  410 ( 1  to  8 ) include, e.g., at various locations within a building, within the interior space of the walls of a building, on street lamps, on billboards, on street signs, and the like. Each transmitter/receiver system  410 ( 1  to  8 ) is coupled to the main base station  550  via a digital fiber transmission line  432 ( 1  to  8 ).  
         [0071]    Within the main base station  550 , receive electronics  454  and transmit electronics  456  are provided. A power distribution unit  158  is also provided within the main base station  550 , and is coupled to both the receive electronics  454  and the transmit electronics  456 . Further, a multiplexer  552  is provided within the main base station  550 . Multiplexer  552  is coupled to each digital fiber transmission line  432 ( 1  to  8 ) that is coupled to the transmitter/receiver systems  410 ( 1  to  8 ). Multiplexer  552  is further coupled to both the receive electronics  454  and the transmit electronics  456 . Consequently, multiplexer  552  is configured to relay signals between the transmitter/receiver systems  410 ( 1  to  8 ) and the receive and transmit electronics  454 ,  456 . Multiplexer  552  processes and relays transmit and receive signals in a manner substantially similar to base station side duplexer  152 , and reference is made to the description of base station side duplexer  152 .  
         [0072]    An alternative embodiment of system  500 , system  600 , is illustrated in FIG. 6. With system  600 , digitizing of analog receive signals, and conversion of digital transmit signals to analog, is accomplished within main base station  650 , rather than in the transmitter/receiver systems  210 ( 1  to n). System  600  includes a plurality of transmitter/receiver systems  210 ( 1  to  8 ). Transmitter/receiver systems  210  have been previously described in the discussion of system  200 , and reference is made to that description. For example, although not shown in FIG. 6, each transmitter/receiver system  210 ( 1  to  8 ) includes a receive side subsystem  120  having an HTS filter  122 , a transmit side subsystem  116 , and first and second transmitter/receiver system duplexers  130 ,  230 . Also, in a similar manner as with system  500 , a greater or smaller number of transmitter/receiver systems  210  may be included in system  600 .  
         [0073]    Because the conversion of signals between analog and digital form is performed within main base station  650 , the transmitter/receiver systems  210 ( 1  to  8 ) do not include DAC, ADC, up-converter units, or down-converter units. Rather, to convert digital transmit signals to analog transmit signals, the main base station  650  includes a DAC  674  coupled to the transmit electronics  454 , and an up-conversion unit  676  coupled to the DAC  674  and the multiplexer  552 . Reference is made to the description of DAC  474  and up-conversion unit  476  of system  400  for details on the operation of DAC  674  and up-conversion unit  676 .  
         [0074]    Additionally, to convert analog receive signals to digital receive signals, the main base station  650  includes an ADC  670  coupled to the receive electronics  456 , and a down-conversion unit  672  coupled to the ADC  670  and the multiplexer  552 . Reference is made to ADC  470  and down-conversion unit  472  for a description of the ADC  670  and down-conversion unit  672 .  
         [0075]    To transmit analog signals between a transmitter/receiver system  210 ( 1  to  8 ) and the base station  650 , a linkage  632 ( 1  to  8 ) is provided. In one embodiment each linkage  632 ( 1  to  8 ) is a digital fiber or optical fiber, similar to transmission line  432 ( 1  to  8 ) of system  500 . In another embodiment, each linkage  632 ( 1  to  8 ) is a remote antenna unit operable to wirelessly transmit analog signals between the transmitter/receiver systems  210 ( 1  to  8 ) and the base station.  
         [0076]    Systems  500 ,  600  are particularly useful for use in telecommunications systems that incorporate standards such as 3G. For example, systems  500 ,  600  provide for a plurality of “underlay” units, which are the transmitter/receiver systems  410 ( 1  to n),  210 ( 1  to n), for a 3G system, and places the underlay units closer to the users of the system. Because the antennas  203  coupled to the transmitter/receiver systems  410 ( 1  to n),  210 ( 1  to n) are located closer to the users, the attenuation of the signals processed by the systems  500 ,  600  decreases. The probability of interfering signals from competitive systems increases, however, because the transmitter/receiver systems  410 ( 1  to n),  210 ( 1  to n) may also be located closer to the users of those systems. The use of superconducting materials within the transmitter/receiver systems  410 ( 1  to n),  210 ( 1  to n), and particularly within the receive side subsystems  420 ,  120 , operates to minimize and eliminate these interfering signals. For example, in telecommunications systems implementing 3G standards, competitors&#39; signals are close in frequency, and the use of superconducting materials within the transmitter/receiver systems  410 ( 1  to n),  210 ( 1  to n) allows systems  500 ,  600  to filter out competitors&#39; signals with greater efficiency and effect than systems that do not incorporate superconducting materials.  
         [0077]    While the invention is susceptible to various modifications and alternative forms, specific examples thereof have been shown in the figures and are described herein in detail. It should be understood, however, that the invention is not to be limited to the particular forms, systems, or methods disclosed. Furthermore, other aspects and embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. The invention is intended to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the appended claims.