Patent Publication Number: US-2006019611-A1

Title: Distributed balanced duplexer

Description:
CROSS-REFERENCE TO A RELATED U.S. PATENT APPLICATION  
      This patent application is related to copending and commonly assigned U.S. patent application Ser. No. 10/672,128 entitled, “Systems and Methods that Employ a Balanced Duplexer” to Phillip J. Mages which was filed on Sep. 26, 2003, the content of which is herein incorporated by reference in its entirety. 
    
    
     TECHNICAL FIELD  
      This invention relates generally to signal processing, and more specifically, relates to a duplexer that employs a distributed balanced filter topology for a transmitter and/or a receiver filter.  
     BACKGROUND  
      In its infancy, mobile communication was based on an analog radio transmission referred to as Advanced Mobile Phone System (AMPS). AMPS provided adequate transmission for an emerging mobile communications consumer market; however, within a few years the emerging market grew to millions of subscribers that demanded more and more airtime, which pushed analog technology to the limit. As a result, dropped calls and busy signals became common, which fueled research and development for an improved mobile communications network.  
      In response, industry developed digital wireless technologies that could accommodate increased network traffic within a limited amount of radio spectrum. One such technology is Global System for Mobile (GSM), which employs Time Division Multiple Access (TDMA). TDMA comprises a time-sharing protocol that provides three to four times more capacity than AMPS. In general, TDMA employs a technique wherein a communication channel is divided into sequential time slices. A respective user of a channel is provided with a time slice for transmitting and receiving information in a round-robin manner. For example, at any given time “t,” a user is provided access to the channel for a short burst. Then, access switches to another user who is provided with a short burst of time for transmitting and receiving information. This cycle continues, and eventually each user is provided with multiple transmission and reception bursts.  
      Shortly after TDMA was introduced, Code Division Multiple Access (CDMA) was developed and represented an enhanced solution to analog transmission. Code Division Multiple Access provides “true” sharing, wherein one or more users can concurrently transmit and receive via employing spread spectrum digital modulation, wherein a user&#39;s stream of bits is encoded and spread across a very wide channel in a pseudo-random fashion. The receiver is designed to recognize and undo the randomization in order to collect the bits for a particular user in a coherent manner. Code Division Multiple Access provides approximately ten times the capacity of analog technologies and enables increased voice quality, broader coverage and increased security. Today, CDMA is the prevalent technology employed in mobile systems.  
      Technological advances paved the way for the mobile communications industry to improve GSM and CDMA technologies and develop new technologies. One such improvement includes EDGE (Enhanced Data-Rates for GSM Revolution) technology. The evolution of GSM to EDGE mitigates various issues associated with voice traffic bandwidth and provides higher data throughput, which increases efficiency and higher performance. For example, EDGE provides for data rates up to 384 Kbps (with a bit-rate up to 69.2 Kbps per timeslot) over broadband. In addition, EDGE provides for more robust services such a Short Message Service (SMS) and Multimedia Message Service (MMS) for messaging, XHTML (including WAP) browsing, Java applications, FM radio reception, video streaming, and voice and image recording technologies.  
      Recently, the International Telecommunications Union adopted an industry standard for third-generation (3G) wireless systems that can provide high-speed data rates (e.g., for data transmission and Internet use) and new features. Currently, three operating modes—CDMA2000, WCDMA and TD-SCDMA—based on CDMA are being developed. CDMA2000 technology provides a relatively simple, quick, and cost-effective path to 3G service. CDMA2000 1×technology supports voice and data services over a standard CDMA channel. Additionally, it provides up to twice the capacity (e.g., peak data rates up to 153 kbps and projected peak data rates up to 307 kbps, without compromising voice capacity) of early CDMA networks. The additional capacity accommodates growth in the Internet market. Moreover, CDMA2000 1×provides longer standby times and is backwards compatible. CDMA2000 1×EV-DO technology provides a data optimized version of CDMA2000 with peak data rates over 2 Mbps and an average throughput of over 700 kbps, which is comparable to DSL and can support video streaming and large file downloads. WCDMA and TD-SCDMA provide more complex enhancements.  
      As mobile communication transmission evolves, the electrical and software industries are concurrently developing mobile devices that are smaller, consume less power, cost less and include more applications. One obstacle confronted by mobile device designers is the need to provide isolators between filtering components and front/back ends. Such isolators can consume valuable space within already densely populated circuitry and increase design complexity.  
     SUMMARY OF THE PREFERRED EMBODIMENTS  
      The foregoing and other problems are overcome, and other advantages are realized, in accordance with the presently preferred embodiments of these teachings.  
      The following presents a simplified summary of the preferred embodiments of the invention in order to provide a basic understanding of some aspects of the invention. This summary is not an extensive overview of the invention. It is not intended to identify key/critical elements of the invention or to delineate the scope of the invention. Its sole purpose is to present some concepts of the invention in a simplified form as a prelude to the more detailed description that is presented later.  
      The present invention relates to a system and method that facilitates concurrent transmission and reception of signals via a distributed balanced duplexer. In general, the system and method employs a three filter duplexer, wherein the filters (e.g., acoustic wave) provide substantially similar input and output impedances (e.g., balanced filter topology). Two of the filters are interfaced to a back-end (e.g., signal generator and processor) and a front-end (e.g., antenna and filter) via two couplers (e.g., 3 dB hybrid couplers such as the Lange or Wilkinson coupler). The third filter is interfaced at the antenna port to increase receiver band impedance which forces the receiver signal to flow into the receiver filter. The receiver&#39;s sensitivity is not degraded as no receiver band power is diverted in the transmission side of the duplexer.  
      Employing 3 dB hybrid couplers within the duplexer decreases reflected RF energy from the filter inputs and outputs and provides for additional band-pass filtering. Employing 3 dB hybrid couplers (e.g., Lange or Wilkinson couplers) provides isolation between the front/back ends and the filters, thus mitigating the need to utilize isolators between such components and facilitating footprint reduction.  
      The couplers provide stable duplexer input and output impedances, which mitigates constraints on filter impedances. The couplers utilize terminating resistors to divert power reflection to maintain the duplexer impedances. Furthermore, the couplers can accommodate any known filters such as the SAW, FBAR, and BAW filters to be integrated within the duplexer.  
      In one non-limiting aspect of the present invention, a system is provided that facilitates transmitting and/or receiving information. The system can be utilized in connection with mobile and stationary communication systems such as mobile phones, web phones, personal data assistants (PDAs), hand-held PCs, pocket PCs, palm-pilots, laptops, tablet PCs, Notepads, GPS devices, pagers, personal computers, mainframes, workstations and other microprocessor-based devices. In general, the system employs a duplexer that provides for concurrent transmission and reception of signals within a frequency band, for example, the cellular and PCS frequency bands. Transmission and reception is isolated, which reduces noise coupling and allows the transmission and receiving components to be positioned closer together.  
      In another non limiting aspect of the present invention, a method is provided for transmitting and receiving signals with devices that utilize the novel aspects of the present invention and constructing systems that employ the novel aspects of the present invention. The transmitting methodology comprises generating a signal, processing the signal for transmission, conveying the signal to a distributed balanced duplexer wherein the signal is split (e.g., via a four channel Lange coupler or discrete component coupler), filtered (e.g. via acoustic wave filters), re-combined (e.g., via the Lange coupler or discrete component coupler) and then conveyed to an output port for transmission (e.g., via an antenna). The receiving methodology comprises the foregoing transmitting system, wherein a signal is received at a port (e.g., antenna and filter), conveyed through at least one filter of the distributed balanced duplexer, and then provided to the device for further processing (e.g., displaying text and images and providing voice).  
      To the accomplishment of the foregoing and related ends, certain illustrative aspects of the invention are described herein in connection with the following description and the annexed drawings. These aspects are indicative, however, of but a few of the various ways in which the principles of the invention may be employed, and the present invention is intended to include all such aspects and their equivalents. Other advantages and novel features of the invention may become apparent from the following detailed description of the invention when considered in conjunction with the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The foregoing and other aspects of these teachings are made more evident in the following Detailed Description of the Preferred Embodiments, when read in conjunction with the attached Drawing Figures, wherein:  
       FIG. 1  illustrates an exemplary transmitting and/or receiving component, in accordance with an aspect of the present invention.  
       FIG. 2  illustrates an exemplary multiplexing component, in accordance with an aspect of the present invention.  
       FIG. 3  illustrates an exemplary distributed balanced duplexer, in accordance with an aspect of the present invention.  
       FIG. 4  illustrates a methodology to employ a distributed balanced duplexer to transmit a signal, in accordance with an aspect of the present invention.  
       FIG. 5  illustrates a methodology to employ a distributed balanced duplexer to receive a signal, in accordance with an aspect of the present invention.  
       FIG. 6  illustrates a methodology to construct a distributed balanced duplexer, in accordance with an aspect of the present invention.  
       FIG. 7  illustrates exemplary front and back ends that can be employed with a distributed balanced duplexer, in accordance with an aspect of the present invention.  
       FIG. 8  illustrates an exemplary wireless communication system wherein the novel aspects of the invention can be employed.  
       FIG. 9  illustrates an exemplary mobile device that can employ the novel aspects of the invention.  
       FIG. 10  illustrates an exemplary network wherein the invention can be employed.  
       FIG. 11  illustrates an exemplary computing environment wherein the invention can be employed. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      The present invention relates to a system and a method for a communication system&#39;s transceiving component that can facilitate concurrent transmission and reception of signals within the system. The system and method utilizes a distributed balanced three-filter duplexer, wherein two filters are connected by two 3 dB hybrid couplers in series with a third transmission filter, wherein the filters can be utilized during signal transmission and reception. The filters are selected such that the input and output impedances are substantially similar, and a coupler (e.g., Lange, Wilkinson, discrete and any 3 dB hybrid coupler) is utilized to provide isolation between the duplexer&#39;s front/back ends and to set and maintain the duplexer&#39;s input and output impedance. Employing such couplers mitigates the need to utilize isolators. The foregoing configuration provides for separation and isolation of transmission and reception, which reduces noise coupling and provides for a design wherein the transmitter and receiver can reside within close proximity. In addition, signal power can be split over the filters during transmission, which enables lower power rated filters to be selected.  
      A non limiting embodiment of the present invention is now described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It may be evident, however, that the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to facilitate describing the present invention.  
       FIG. 1  illustrates an exemplary transceiving component  100  that can be employed to facilitate transmitting and/or receiving information between systems, in accordance with a non limiting embodiment of the present invention. The transceiving component  100  can be utilized in connection with mobile (ambulatory and portable) and stationary communication systems. Examples of suitable mobile systems include, but are not limited to, mobile phones (e.g., cellular and PCS), web phones, personal data assistants (PDAs), hand-held PCs, pocket PCs, palm-pilots, laptops, tablet PCs, Notepads, GPS devices and pagers. Examples of stationary systems include conventional personal computer (e.g., desktop, mini-tower and tower), mainframes, workstations and other microprocessor-based devices. In order to be utilized with the foregoing mobile and stationary systems, it is to be appreciated that the transceiving component  100  can be implemented in hardware, software and/or firmware.  
      The transceiving component  100  can provide isolation (e.g., via coupling components) between itself and other components. For example, the transceiving component  100  can be interfaced with a back-end (not shown) without having to employ an isolator between the transceiving component  100  and the back-end (e.g., signal processor). Likewise, the transceiving component  100  can be interfaced with a front-end (not shown) without having to employ an isolator between the transceiving component  100  and the front-end (e.g., antenna, etc.). Conventional systems typically employ isolating components between the back and front ends. Thus, the present invention mitigates the need for utilizing isolators when integrating the transceiving component  100  into communication systems, which can reduce cost and size and simplify the design. Such reductions can be exploited and are advantageous since the technology market demands smaller footprints and lower prices with every new generation.  
      In addition, the transceiving component  100  can provide stable and substantially similar input and output impedances (e.g., typically 50 Ω), which facilitates achieving maximum power transfer via matching back and front end impedances with input and output impedances, respectively. Power reflections can be transferred to suitable terminations to maintain the input and output impedances.  
      The transceiving component  100  comprises a transmitter component  110  that facilitates sending information and a receiver component  120  that facilitates accepting information. The novel aspects of the transceiving component  100  provide for separation of and isolation between the transmitter component  110  and the receiver component  120 , which can reduce noise in either or both components caused by power coupling. The separation and isolation can be advantages when employing the transceiving component  100  on a printed circuit board (PCB) since it allows the transmitter component  110  and receiver component  120  to be positioned proximate to each other, and hence reside within a reduced footprint since no isolator is required, while mitigating noise due to power coupling.  
      The transceiving component  100  can employ a means that defines frequency bands in which signals can be transmitted and/or received. In general, transmitted signals leave the transceiving component  100  through the transmitter component  110 . In one non limiting embodiment of the present invention, the transmitter component  110  can be utilized as an antenna wherein the signal is transmitted from the transmitter component  110 . In other non limiting embodiments of the invention, the transmitter component  100  provides a channel to convey the signal to an antenna or signal-processing component. Received signals are conveyed to the transceiving component  110  through the receiver component  120 . The receiver component  120  can be an antenna employed to receive the signal or the signal can be conveyed through the receiver component  120  after being received via an antenna.  
      As noted above, the transceiving component  100  can be implemented in software, hardware and/or firmware. For example, transceiving component  100  can be a process running on a processor, a processor, an object, an executable instruction, a thread of execution, and/or a program. In another example, off-the-shelf and/or proprietary hardware, such as signal processors (e.g., DSPs), filters, couplers (e.g., splitter and combiners), and Application Specific Integrated Chips (ASICs) can be employed in connection with the transceiving component  100 . Firmware can be utilized to provide low-level executable instructions, parameters and/or control code, and provide a flexible means to upgrade and/or revise hardware functionality and performance. Moreover, transceiving component  100  can be localized within an individual device and/or distributed across two or more devices.  
      It is to be appreciated that the transceiving component  100  can be implemented within a PCB (or Printed Wire Board (PWB)) such as a daughter board connected to a motherboard or integrated within the motherboard. A typical PCB that can be utilized in accordance with a non limiting embodiment of the present invention comprises a non-conducting substrate (e.g., fiberglass with epoxy resin or ceramic substrate) upon which conductive patterns can be formed. Conductive patterns usually are constructed with copper; however, other conductive material such as nickel, silver, tin, tin-lead, gold and the like can be utilized. For example, a conductive material can be concurrently employed as etch-resists and/or top-level metal (e.g., “tinning” the surface with solder). In addition, conductive patterns can be formed within multiple layers, wherein the layers are connected by vias. Moreover, the PCB can be manufactured to be as rigid or as flexible as desired. Thus, the PCB can be designed for environments with various levels of vibration, pressure, temperature, shape, etc.  
      Where the transceiving component is implemented as a daughter board, the board can be mounted to the motherboard through any known means for fastening such as standoffs, connectors, expansion slots, mounting screws, sockets, right angle brackets, etc. In addition, the daughter board can be mounted directly to the motherboard or via another daughter board. Moreover, communication can be achieved between the daughter board and the motherboard via electrical, mechanical, optical, RF and/or infrared mediums.  
      The PCB can be single or double sided and/or multilayered and populated with passive and active circuitry via embedded, surface, ball and/or wire mount. Suitable components include filters, couplers, resisters, capacitors (e.g., bypass and coupling), inductors, various solid state devices including transistors and operational amplifiers, digital signal processors (DSPs), integrated circuits (ICs), multi-layered components such as ASICs with analog, digital and/or RF layers, multichip modules (MCMs), plastic encapsulated chips (PEMs) and microwave monolithic integrated circuits (MMICs)  
      Integrated chips and derivatives thereof can be surface mount and based on unpackaged (“bare”) and/or flip chip technology. As known, unpackaged chips utilize bare chip dies attached to an unprocessed support substrate, wherein fabrication can occur on top of the die, resulting in modules with the ICs buried beneath the interconnect and associated ground and power planes and with no bond wires. In addition, bare chips can be mounted on a previously patterned substrate. Flip chips generally are unpackaged chips that are mounted face down for direct contact with the substrate. Employing unpackaged and flip chips provide for reduced (e.g., thin) package profiles. Die sizes can be increased, as desired, to improve heat dissipation.  
       FIG. 2  illustrates a system  200  that can be employed to separate transmitted and received signals. The system  200  comprises a multiplexer (“MUX”)  210  that can provide for serial and/or concurrent transmission and reception of a plurality of signals. In order to multiplex, MUX  210  can comprise various signal splitting and combining components and intermediate signal processing components. The splitting and combining components can include couplers such as directional (e.g., 3 dB) and hybrid couplers (e.g., 3 dB/Quadrature hybrid).  
      The intermediate components can include, for example, one or more filters such as low, high or band pass/reject discrete and/or acoustic wave filters, packaged in ceramic, “bare” and/or flip chips configurations. Discrete ceramic filters provide an inexpensive, high power handling and high performance approach while acoustic filters provide high performance and selectivity, and generally are more compact then their discrete sister filters.  
      Acoustic wave filters include surface acoustic wave (SAW) and bulk acoustic wave (BAW) filters. Both types of acoustic filters utilize the piezoelectric effect to convert electrical/mechanical energy into mechanical/electrical energy via material deformation when an RF signal is applied. In the SAW filter, energy is propagated on the surface, whereas BAW filters direct energy throughout the bulk. As briefly noted above, acoustic filters generally are compact; the SAW filter typically comprises multi-chip modules and the BAW filter can be fully integrated on a chip (“system of a chip” technology). BAW filters can be further delineated by the design approach. For example, both the Film Bulk Acoustic Resonator (FBAR) and the Soldily Mounted Resonator (SMR) can be employed as BAW filters, but they vary in design approach. The FBAR filter is designed via a membrane approach, wherein a thin Si x N y  film is applied to a substrate to construct a resonator. The SMR filter is designed via a mirror approach, wherein a stack of low and high impedance quarter-wave layers (mirrors) are employed to construct a resonator. Such filters can be employed to define frequency bands in which signals can be transmitted and/or received.  
      The system  200  can be employed in connection with or as part of the transceiving component  100 . As such, the system  200  can provide many of the benefits described above. For example, the system  200  can provide an isolation barrier  220  with a back-end. The isolation barrier  220  mitigates the need to employ an isolating component between the back-end and MUX  210 . In addition, the system  200  can provide an isolation barrier with a front-end, including a transmit port (“Tx”)  240  and a receive port (“Rx”)  250 . Similarly, the isolation barrier  230  mitigates the need to employ an isolating component between the front-end and MUX  210 . As noted previously, mitigating the need for isolating components can simplify design and reduce size and cost.  
      In addition, the system  200  can provide for matching MUX  210  input and output impedances, which facilitates achieving maximum power transfer between MUX  210  and the back and front ends and reduces losses due to power reflections. The means for matching the input and output impedances can additionally reduce the constraints on intermediate components utilized within MUX  210 . For example, when filters are employed within MUX  210 , selection of filters is not constrained within a range of input and output impedances. Furthermore, the MUX  210  can provide a buffer at the input and/or output stages.  
      Tx  240  can provide a pass-through for transmission or be any known device utilized for transmitting signals, such as an antenna. In addition, Tx  240  can include mechanisms to modulate, encrypt and/or encode the signal. Rx  250  can provide a pass-through for reception or be any known device utilized for transmitting signals, such as an antenna, and/or a coupling device (e.g., coaxial cable, A/D converter, opto coupler). When modulated, encrypted and/or encoded signal are received, suitable signal processing can be employed in connection with Rx  250  to demodulate, decrypt and/or decode the signals.  
      MUX  210  can further provide for separation of and isolation between Tx  240  and Rx  250 . The separation of and isolation can reduce cross power contamination (noise) between Tx  240  and Rx  250 , which can enable Tx  240  and Rx  250  to be positioned closer together, which can facilitate reducing the footprint of MUX  210 .  
       FIG. 3  illustrates an exemplary distributed balanced duplexer  300 , in accordance with a non limiting embodiment of the present invention. The distributed balanced duplexer  300  can be utilized to facilitate transmitting and receiving signals. Examples of systems that can employ the distributed balanced duplexer  300  include the transceiving component  100  and the system  200 , mobile communication systems such as cell phones, satellite communication systems, computer networks, global positioning systems, and radios.  
      The distributed balanced duplexer  300  comprises a first filter (“filter A”)  310 , a second filter (“filter B”)  320  and a third filter (“filter C”)  396 . In general, the filters  310 ,  320  can be tuned to transmit and receive within desired transmit and receive frequency bands. The filters  310 ,  320  can be configured for the frequency bands by utilizing various low, high and band pass/reject techniques. For example, the filters  310 ,  320  can be designed to transmit and receive signals within the Cellular band, which typically is associated with frequencies around 850 MHz. In another example, the filters  310 ,  320  can be designed to transmit and receive signals within the PCS band, which typically is associated with frequencies around 1900 MHz. In yet another example, the filters  310 ,  320  can be designed to receive signals within the GPS band, which typically is associated with frequencies around 1600 MHz.  
      The filters  310 ,  320 ,  396  can be implemented as discrete components such as resistors, capacitors, etc. and/or chips including plastic encapsulated modules (PEMs), monolithic microwave integrated chips (MMICs), and application specific integrated chips (ASICs). In one non limiting embodiment of the present invention, the filters  310 ,  320 ,  396  can be employed with variable capacitors or other elements that provide a means to calibrate and adjust the frequency band and/or vary the frequency band.  
      The filters  310 ,  320 ,  396  can be any known type of filter; however, acoustic filters typically are employed. Examples of suitable acoustic filters include SAW and BAW (e.g., FBAR and SMR) filters. As known, acoustic filters employ a piezo technique, wherein electric/mechanical energy is converted to mechanical/electrical energy. For example, in the SAW filter, energy travels longitudinal to the surface of the filter and in the BAW filter, energy additionally travels into the bulk of the filter. Acoustic filters provide high performance and selectivity within a relatively small package ranging from multi-chip modules to fully integrated systems on a chip.  
      The distributed balanced duplexer  300  further comprises a first coupler  330  that interfaces the filters  310 ,  320  with a back-end of a system. For example, the first coupler  330  can establish a path  340  from a signal-generating component (e.g., a component that generates a signal for transmission) to at least one of the filters  310 ,  320  and/or from at least one of the filters  310 ,  320  to a signal-conditioning component. In addition, the first coupler  330  can provide an isolated path  350  to the filters  310 ,  320  that can be terminated to ground via an impedance-setting resistor  360 . As depicted, the resistor  360  can be a 50 Ω resistor, which is a standard termination impedance. However, it is to be appreciated that the any value resistance suitable for a design can be employed.  
      A second coupler  370  interfaces the filters  310 ,  320  with a front-end of a system. The second coupler  370  establishes a path  380  from at least one of the filters  310 ,  320  to the third filter  396 . The third filter  396  is coupled to a transmitting device  390  such as an antenna and then to a receiver filter  398 . Similar to the back-end, the second coupler  370  can provide an isolated path  392  from at least one of the filters  310 ,  320  that can be terminated to ground via an impedance-setting resistor  394 . Likewise, the resistor  394  can be various valued and typically is a 50 Ω resistor.  
      The preferred couplers  330 ,  370  are 3 dB hybrid coupler such as a Lange or discrete coupler. However, it is to be appreciated that various other couplers (e.g., directional coupler) can be employed in accordance with an aspect of the present invention. Utilizing a Lange coupler provides the benefit of additional band-pass filtering via coupler trace shape and/or size. In addition, the Lange coupler can be implemented as conductive traces (e.g., gold, silver and copper) on a substrate, which can be employed to integrate the couplers  330 ,  370  with the filters  310 ,  320 .  
      In general, the Lange coupler can be implemented as a three-wire, four-port coupler. During transmission, the path  340  is utilized as an input to the first coupler  330 . The first coupler  330  splits the signal power such that a portion of the signal power passes through the second filter  320  and the remaining portion of signal power is coupled to pass through the first filter  310 . A coupling coefficient (e.g., a power ratio) can be utilized to determine the portion of power that passes through respective filters  310 ,  320 . In one aspect of the present invention, a coupling coefficient is provided such that about half the power travels through respective filters  310 ,  320 . Thus, respective filters  310 ,  320  can be rated at one half the total power rating, which enables a designer to utilize lower power rated components. The second coupler  370  combines the signals from the filters  310 ,  320  and conveys the signal to the third filter  396  and then to the transmitting component  390  via path  380 .  
      As described above, transmission via the duplexer  300  utilizes filters  310 ,  320 . Typically, the input and output impedances of the filters  310 ,  320  are matched (e.g., 50 Ω) to provide a balanced topology. However, it can be appreciated that in other non limiting embodiments of the present invention, that only one of the filters  310 ,  320  is employed during transmission. The ability to employ one or both filters  310 ,  320  provides a mechanism wherein if one of the filters  310 ,  320  fails, the duplexer  300  continues to function with the other filter (e.g., with a 3 dB loss).  
      In other aspects of the present invention, the transmitting component  390  can be employed as a receiver. As such, the path  380  can interface the received signal with the second coupler  370 .  
      The isolation paths  350 ,  392  provide isolation between the couplers  330 ,  370  and the back and front ends, respectively. Thus, employing the present invention mitigates the need to utilize an isolation component between the couplers  330 ,  370  and the back and front ends, which can reduce size and render a simpler design.  
      In addition, terminating the couplers  330 ,  370  with 50 Ω resistors mitigates the constraint of requiring 50 impedance filters  310 ,  320 . Instead, the couplers  330 ,  370  in connection with the balanced topology (matched input/output impedances) can maintain 50 Ω input and output impedances by diverting reflected power into the 50 Ω terminating resistors.  
      Distributed balanced duplexer  300  can improve impedance matching by reducing reflected energy from the filters  310 ,  320  between the couplers  330 ,  370 . For example, one of the filters  310 ,  320  can be operative to a pass-through path and the other filter can be operative to a coupled path. When the input signal is split, a portion of signal can be conveyed to the pass-through path with zero degree phase shift and the remaining portion can be conveyed to the coupled path with 90 degree phase shift. Reflected energy returns to the input with zero degrees phase shift from the pass-through path and 180 degrees phase shift (90 degrees plus an additional 90 phase shift) from the coupled path, thereby canceling each other out at the input. In addition, any residual reflected energy from the coupled path can be dissipated in the 50 Ω resistor.  
      Distributed balanced duplexer  300  adds another transmission filter  396  at the antenna  390 , thereby increasing the receiver band impedance enabling the receiver signal to flow into the receiver filter  398 . Additionally, the third filter  396  provides isolation between the balanced filters  310 ,  320  and the antenna  390 , while eliminating the need for an external directional coupler. The receiver&#39;s sensitivity is not degraded as no receiver band power is diverted to the front end of the duplexer.  
       FIGS. 4-6  illustrate methodologies, in accordance with a non limiting embodiment the present invention. While, for purposes of simplicity of explanation, the methodologies are shown and described as a series of acts, it is to be understood and appreciated that the present invention is not limited by the order of acts, as some acts can, in accordance with the present invention, occur in different orders and/or concurrently with other acts from that shown and described herein. For example, those skilled in the art will understand and appreciate that a methodology could alternatively be represented as a series of interrelated states or events, such as in a state diagram. Moreover, not all illustrated acts may be required to implement a methodology in accordance with the present invention.  
       FIG. 4  illustrates a methodology  400  that employs a distributed balanced duplexer to transmit a signal, in accordance with a non limiting embodiment of the present invention. Proceeding to reference numeral  410 , a signal generator is employed to generate a signal with information that is to be transmitted. At  420 , the signal can be suitably processed for transmission. For example, the signal can be amplified, phase shifted, encrypted, encoded, modulated and/or wrapped in a carrier.  
      At  430 , the processed signal can be conveyed to a distributed balanced duplexer. The signal can pass through a coupler (e.g., 3 dB hybrid such as a Lange) to one or more filters, wherein the signal power can be split amongst the filters (e.g., as defined via a power ratio). Splitting the power allows for utilization of lower power rated filters, which typically are smaller than higher power rated filters. The filters typically provide a band pass frequency region via low, high and/or band pass/reject filters. At  440 , the signals are combined via a second coupler and conveyed to a transmitting component such as an antenna.  
       FIG. 5  illustrates a methodology  500  that employs a distributed balanced duplexer to receive a signal, in accordance with a non limiting embodiment of the present invention. At reference numeral  560 , a signal is received. The received signal can be phase shifted, encrypted, encoded, modulated and/or wrapped in a carrier. At  570 , the signal is conveyed to a distributed balanced duplexer. It is to be appreciated that the distributed balanced duplexer can comprise a plurality of filters and that one or more of the plurality of filters can be utilized to process the received signal. At reference numeral  480 , the received signal passes through the duplexer to a signal processing stage that can be a pass through or include a means for signal amplification, conditioning, decryption, decoding, demodulation and/or carrier extraction.  
      Turning to  FIG. 6 , a methodology  600  to construct a novel distributed balanced duplexer is illustrated. Proceeding to reference numeral  610 , a PCB or substrate is procured for the duplexer. As provided above, a typical PCB comprises a non-conducting substrate with conductive patterns formed with one or more layers. The PCB can be single or double sided and/or multilayered and populated with passive and active circuitry via embedded, surface, ball and/or wire mount. Suitable components include filters, couplers, resistors, capacitors (e.g., bypass and coupling), inductors, various solid state devices including transistors and operational amplifiers, digital signal processors (DSPs), integrated circuits (ICs), multi-layered components such as ASICs with analog, digital and/or RF layers, multichip modules (MCMs), plastic encapsulated chips (PEMs) and microwave monolithic integrated circuits (MMICs). Integrated chips and derivatives thereof can be surface mounted and based on unpackaged (“bare”) and/or flip chip technology. Various fastening means can be employed to couple the duplexer PCB with other components. For example, standoffs, connectors, expansion slots, mounting screws, sockets, right angle brackets, etc. can be employed. In addition, the PCB can be mounted directly to another component or to another PCB.  
      At reference numeral  620 , the duplexer can be constructed on the PCB. In one aspect of the present invention, the duplexer is formed from two couplers (e.g., Lange) and three acoustic (e.g., SAW, FBAR and SMR) filters configured in a distributed balanced topology. One coupler is employed at the back-end of the duplexer, wherein the coupler provides isolation between the back-end and the filters. In addition, an isolation lead from the coupler is terminated with 50 Ω resistor to provide a path to divert power reflections into in order to maintain an impedance of 50 Ω. The other coupler is employed at the front-end of the duplexer and provides isolation between the front-end and the filters. Two of the filters reside between the couplers, wherein both filters are employed for signal transmission and one filter is employed for signal reception.  
      At reference numeral  630 , a back end is interfaced to the duplexer. Since the duplexer provides isolation, an isolating component need not be employed between the back-end and the duplexer. At reference numeral  640 , a front-end is interfaced to the duplexer. A third filter resides at the antenna port, increasing receiver band impedance enabling the receiver signal to flow into the receiver filter.  
       FIG. 7  illustrates an exemplary transmitting and receiving system  700 , in accordance with a non limiting embodiment of the present invention. The system  700  comprises a duplexer  705  coupled to a receiving system  710  and a transmitting system  745 . The duplexer  705  can be a distributed balanced duplexer and/or employed in connection with a transceiving component, as described herein.  
      The receiving system  710  comprises a plurality of stages including pre-processing, mixing, phase shifting, and amplifying. It is to be appreciated that the stages and associated components depicted in the receiving system  710  provide for one example, and the various other configurations including additional and/or different stages and components can be employed in accordance with as aspect of the present invention. For example, the phase shifting stage can occur prior to the mixing stage.  
      The receiving system  710  can be employed to receive signals such as RF signals (e.g., extremely high frequency signals) and/or signals outside the RF band. The receiving component  715  can be, for example, an antenna associated with a spacecraft, a satellite, an aircraft, an automobile, a mobile device, or an amphibious vehicle. After receiving the signal, the receiving component  715  (e.g., an antenna) can convey the signal to the preprocessing component  720  through the duplexer  705 , as described in detail above.  
      The pre-processing component  720  can filter the noise in the signal. For example, RF signals typically are associated with low power levels (e.g., near the noise floor), and can be processed with a low-noise amplifier (LNA). When the gain of the LNA is sufficiently large, the noise contribution from the remaining stages of the receiving system  710  can be relatively small since the noise added via the other stages is divided by the gain of the LNA and the LNA gain and noise figure (the measure of noise added by the LNA) determine the receiver noise characteristics. The preprocessing component  720  can additionally be employed to band pass filter the signal.  
      After pre-processing, the signal can be conveyed to the mixer  725 . In general, mixers convert an input at one frequency to an output at another frequency (e.g., an intermediate frequency (IF)) to permit filtering, phase shifting, and/or other data processing operation at a frequency more easily implemented by the circuits. The oscillator  730  can generate a local oscillator (LO) signal that can be fed into the mixer, wherein the mixer  725  can generate the output signal via combining the signal from the pre-processor  720  with the LO signal from the oscillator  730  to generate a signal at the intermediate frequency (IF) (e.g., fRF-fLO or fLO-fRF) and harmonics of the IF, RF, and LO frequencies.  
      For example, the receiving system  710  can be employed to acquire data within a band from 75 to 110 GHz. Filters associated with this band can have low Q or high loss, which degrades the receiver noise characteristics. Therefore, it can be advantageous to shift the received signal&#39;s frequency to a lower value where low-loss filters can be utilized. Typically, this is achieved without degrading the input signal&#39;s amplitude or introducing additional noise. The conversion efficiency of the mixer usually depends on the LO drive power.  
      The mixed signal can be conveyed to the phase shifter  735  for signal modulation (e.g., phase shift key modulation). In addition, the phase shifter  735  can include DC bias, RF matching and/or high Q RF short circuitry. The DC bias circuitry can be employed to vary the level of DC bias to affect the impedance state, the RF matching circuitry can be employed to pass signals within a desired frequency band, maximize power and/or block frequencies, and the high Q RF short circuitry can be employed to provide an RF short for the DC lines.  
      After phase shifting, the amplifier  740  can be utilized to increase the power, or gain of the signal (e.g., via transconductance or current). The number of stages in the amplifier typically is dependent on the desired gain and frequency, since transistor output power decreases with increasing frequency. The amplified signal can then be further processed and/or utilized.  
      Similar to the transmitting system  710 , the receiving system  745  comprises a plurality of stages including amplification, mixing, phase shifting, and signal conditioning. Likewise, the various stages and associated components depicted in the receiving system  745  provide for one example, and the various other configurations including additional and/or different stages and components can be employed in accordance with as aspect of the present invention.  
      The transmitting system  745  comprises an amplifier  750  that amplifies signal power. The amplified signal can be conveyed to the mixer  755 , wherein the mixer  755  can generate a signal at an intermediate frequency from the amplified signal and a signal from the local oscillator  760 , as described above.  
      After generating the intermediate frequency signal, the phase shifter  770  can be employed to phase shift the signal. Various phase shifting techniques can be employed including utilizing binary, reflective, hybrid reflective and switched phase filters. The phase-shifted signal can be conditioned prior to being transmitted via the signal conditioner  780 . For example, the signal can be encrypted, encoded, and/or encapsulated within an envelope. In another example, the signal can be filtered. The power amplifier  790  can be employed to increase the gain of the signal. The transmitting component  745 , can convey the signal via the duplexer  705  to antenna  795  for transmission.  
       FIG. 8  illustrates an exemplary mobile communications environment (“environment”)  800 , in accordance with an aspect of the present invention. The environment  800  comprises a wireless communication device (“device”)  810 , a cellular transceiver  820 , a PCS transceiver  830 , a GPS transmitter  840  and a wireless network  850  (e.g., Bluetooth and Wi-Fi).  
      The device  810  can include or be employed in connection with the components, systems and methods described herein. For example, the device  810  can include a transceiving component or duplexer. Furthermore, the device  810  can include a CDMA antenna, a GPS antenna and a Bluetooth antenna. In addition, enhanced and other transmission technologies (e.g., CDMA2000, WCDMA and TD-SCDMA) and other various other antenna configurations can be utilized in accordance with an aspect of the invention.  
      The device  810  can employ various mobile communication technologies to communicate with the cellular transceiver  820 , the PCS transceiver  830 , the GPS transmitter  840  and the wireless network  850 . For example, the device  810  can transmit cellular information to and/or receiver cellular information from the cellular transceiver  820 . Likewise, the device can transmit and/or receive information with the wireless network  850 , for example with one or more devices employing Bluetooth technology or Wi-Fi/WLAN such as a PDA, a printer, a copier, a facsimile, a scanner, a display, a computer, a microprocessor and/or another mobile communication device similar to the device  810 .  
       FIG. 9  illustrates an exemplary mobile (e.g., portable and wireless) telephone  900  that can employ the non limiting embodiments of the present invention. The mobile telephone  900  comprises an antenna  905  that communicates (e.g., transmit and receive) radio frequency signals with one or more base stations. The antenna  905  can be coupled to duplexer circuitry (e.g., as described herein) within the mobile telephone  900 . In addition, the mobile telephone  900  can include a separate signal-receiving component (not shown) that can also be coupled to the duplexer.  
      The mobile telephone  900  further comprises a microphone  910  that receives audio signals and conveys the signals to at least one on-board processor for audio signal processing, and an audio speaker  915  for outputting audio signals to a user, including processed voice signals of a caller and recipient music, alarms, and notification tones or beeps. Additionally, the mobile telephone  900  can include a power source such as a rechargeable battery (e.g., Alkaline, NiCAD, NiMH and Li-ion), which can provide power to substantially all onboard systems when the user is mobile.  
      The mobile telephone  900  can further include a plurality of multi-function buttons including a keypad  920 , menu navigating buttons  925  and on-screen touch sensitive locations (not shown) to allow a user to provide information for dialing numbers, selecting options, navigating the Internet, enabling/disabling power, and navigating a software menu system including features in accordance with telephone configurations. A display  930  can be provided for displaying information to the user such as a dialed telephone number, caller telephone number (e.g., caller ID), notification information, web pages, electronic mail, and files such as documents, spreadsheets and videos. The display  930  can be a color or monochrome display (e.g., liquid crystal, CRT, LCD, LED and/or flat panel), and employed concurrently with audio information such as beeps, notifications and voice. Where the mobile telephone  900  is suitable for Internet communications, web page and electronic mail (e-mail) information can also be presented separately or in combination with the audio signals.  
      The menu navigating buttons  925  can further enable the user to interact with the display information. In support of such capabilities, the keypad  920  can provide keys that facilitate alphanumeric input, and are multifunctional such that the user can respond by inputting alphanumeric and special characters via the keypad  920  in accordance with e-mail or other forms of messaging communications. The keypad keys also allow the user to control at least other telephone features such as audio volume and display brightness.  
      An interface can be utilized for uploading and downloading information to memory, for example, the reacquisition time data to the telephone table memory, and other information of the telephone second memory (e.g., website information and content, caller history information, address book and telephone numbers, and music residing in the second memory). A power button  940  allows the user to turn the mobile telephone  900  power on or off.  
      The mobile telephone  900  can further include memory for storing information. The memory can include non-volatile memory and volatile memory, and can be permanent and/or removable. The mobile telephone  900  can further include a high-speed data interface  945  such as USB (Universal Serial Bus) and IEEE 1394 for communicating data with a computer. Such interfaces can be used for uploading and downloading information, for example website information and content, caller history information, address book and telephone numbers, and music residing in the second memory. In addition, the mobile telephone  900  can communicate with various input/output (I/O) devices such as a keyboard, a keypad, and a mouse.  
      In order to provide a context for the various aspects of the invention,  FIGS. 10 and 11  as well as the following discussion are intended to provide a brief, general description of a suitable computing environment in which the various aspects of the present invention can be implemented. While the invention has been described above in the general context of computer-executable instructions of a computer program that runs on a computer and/or computers, those skilled in the art will recognize that the invention also can be implemented in combination with other program modules. Generally, program modules include routines, programs, components, data structures, etc. that perform particular tasks and/or implement particular abstract data types. Moreover, those skilled in the art will appreciate that the inventive methods may be practiced with other computer system configurations, including single-processor or multiprocessor computer systems, mini-computing devices, mainframe computers, as well as personal computers, hand-held computing devices, microprocessor-based or programmable consumer electronics, and the like. The illustrated aspects of the invention may also be practiced in distributed computing environments where task are performed by remote processing devices that are linked through a communications network. However, some, if not all aspects of the invention can be practiced on stand-alone computers. In a distributed computing environment, program modules may be located in both local and remote memory storage devices.  
       FIG. 10  illustrates an exemplary computing environment  1000  in which the present invention can be employed. The system  1000  includes one or more client(s)  1010 . The client(s)  1010  can be hardware and/or software (e.g., threads, processes, computing devices). The system  1000  additionally includes one or more server(s)  1030 . Likewise, the server(s)  1030  can be hardware and/or software (e.g., threads, processes, computing devices). One possible communication between a client  1010  and a server  1030  can be in the form of a data packet transmitted between two or more computer processes. The system  1000  further includes a communication framework  1050  that can be employed to facilitate communications between the client(s)  1010  and the server(s)  1030 . The client(s)  1010  can interface with one or more client data store(s)  1060 , which can be employed to store information local to the client(s)  1010 . Similarly, the server(s)  1000  can interface with one or more server data store(s)  1040 , which can be employed to store information local to the servers  1030 .  
      With reference to  FIG. 11 , an exemplary environment  1110  for implementing various aspects of the invention includes a computer  1112 . The computer  1112  includes a processing unit  1114 , a system memory  1116 , and a system bus  1118 . The system bus  1118  couples system components including, but not limited to, the system memory  1116  to the processing unit  1114 . The processing unit  1114  can be any of various available processors. Dual microprocessors and other multiprocessor architectures also can be employed as the processing unit  1114 .  
      The system bus  1118  can be any of several types of bus structure(s) including the memory bus or memory controller, a peripheral bus or external bus, and/or a local bus using any variety of available bus architectures including, but not limited to, 8-bit bus, Industrial Standard Architecture (ISA), Micro-Channel Architecture (MSA), Extended ISA (EISA), Intelligent Drive Electronics (IDE), VESA Local Bus (VLB), Peripheral Component Interconnect (PCI), Universal Serial Bus (USB), Advanced Graphics Port (AGP), Personal Computer Memory Card International Association bus (PCMCIA), and Small Computer Systems Interface (SCSI).  
      The system memory  1116  includes volatile memory  1120  and nonvolatile memory  1122 . The basic input/output system (BIOS), containing the basic routines to transfer information between elements within the computer  1112 , such as during start-up, is stored in nonvolatile memory  1122 . By way of illustration, and not limitation, nonvolatile memory  1122  can include read only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable ROM (EEPROM), or flash memory. Volatile memory  1120  includes random access memory (RAM), which acts as external cache memory. By way of illustration and not limitation, RAM is available in many forms such as synchronous RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double data rate SDRAM (DDR SDRAM), enhanced SDRAM (ESDRAM), Synchlink DRAM (SLDRAM), and direct Rambus RAM (DRRAM).  
      Computer  1112  also includes removable/non-removable, volatile/non-volatile computer storage media.  FIG. 11  illustrates, for example a disk storage  1124 . Disk storage  1124  includes, but is not limited to, devices like a magnetic disk drive, floppy disk drive, tape drive, Jaz drive, Zip drive, LS- 100  drive, flash memory card, or memory stick. In addition, disk storage  1124  can include storage media separately or in combination with other storage media including, but not limited to, an optical disk drive such as a compact disk ROM device (CD-ROM), CD recordable drive (CD-R Drive), CD rewritable drive (CD-RW Drive) or a digital versatile disk ROM drive (DVD-ROM). To facilitate connection of the disk storage devices  1124  to the system bus  1118 , a removable or non-removable interface is typically used such as interface  1126 .  
      It is to be appreciated that  FIG. 1  describes software that acts as an intermediary between users and the basic computer resources described in suitable operating environment  1110 . Such software includes an operating system  1128 . Operating system  1128 , which can be stored on disk storage  1124 , acts to control and allocate resources of the computer system  1112 . System applications  1130  take advantage of the management of resources by operating system  1128  through program modules  1132  and program data  1134  stored either in system memory  1116  or on disk storage  1124 . It is to be appreciated that the present invention can be implemented with various operating systems or combinations of operating systems.  
      A user enters commands or information into the computer  1112  through input device(s)  1136 . Input devices  1136  include, but are not limited to, a pointing device such as a mouse, trackball, stylus, touch pad, keyboard, microphone, joystick, game pad, satellite dish, scanner, TV tuner card, digital camera, digital video camera, web camera, and the like. These and other input devices connect to the processing unit  1114  through the system bus  1118  via interface port(s)  1138 . Interface port(s)  1138  include, for example, a serial port, a parallel port, a game port, and a universal serial bus (USB). Output device(s)  1140  use some of the same type of ports as input device(s)  1136 . Thus, for example, a USB port may be used to provide input to computer  1112 , and to output information from computer  1112  to an output device  1140 . Output adapter  1142  is provided to illustrate that there are some output devices  1140  like monitors, speakers, and printers, among other output devices  1140 , which require special adapters. The output adapters  1142  include, by way of illustration and not limitation, video and sound cards that provide a means of connection between the output device  1140  and the system bus  1118 . It should be noted that other devices and/or systems of devices provide both input and output capabilities such as remote computer(s)  1144 .  
      Computer  1112  can operate in a networked environment using logical connections to one or more remote computers, such as remote computer(s)  1144 . The remote computer(s)  1144  can be a personal computer, a server, a router, a network PC, a workstation, a microprocessor based appliance, a peer device or other common network node and the like, and typically includes many or all of the elements described relative to computer  1112 . For purposes of brevity, only a memory storage device  1146  is illustrated with remote computer(s)  1144 . Remote computer(s)  1144  is logically connected to computer  1112  through a network interface  1148  and then physically connected via communication connection  1150 . Network interface  1148  encompasses communication networks such as local-area networks (LAN) and wide-area networks (WAN). LAN technologies include Fiber Distributed Data Interface (FDDI), Copper Distributed Data Interface (CDDI), Ethernet/IEEE 802.3, Token Ring/IEEE 802.5 and the like. WAN technologies include, but are not limited to, point-to-point links, circuit switching networks like Integrated Services Digital Networks (ISDN) and variations thereon, packet switching networks, and Digital Subscriber Lines (DSL).  
      Communication connection(s)  1150  refers to the hardware/software employed to connect the network interface  1148  to the bus  1118 . While communication connection  1150  is shown for illustrative clarity inside computer  1112 , it can also be external to computer  1112 . The hardware/software necessary for connection to the network interface  1148  includes, for exemplary purposes only, internal and external technologies such as, modems including regular telephone grade modems, cable modems and DSL modems, ISDN adapters, and Ethernet cards.  
      What has been described above includes examples of the present invention. It is, of course, not possible to describe every conceivable combination of components or methodologies for purposes of describing the present invention, but one of ordinary skill in the art may recognize that many further combinations and permutations of the present invention are possible. Accordingly, the present invention is intended to embrace all such alterations, modifications, and variations that fall within the spirit and scope of the appended claims.