Abstract:
A multi-beam, polarization diversity, narrow-band cognitive antenna system is disclosed. The antenna system includes a plurality of antenna elements, switching elements, and transmission feed lines disposed on a PCB substrate, inside or on the enclosure of a consumer wireless device, on the airframe of an air vehicle, or on the surface of a ground vehicle. The plurality of switching elements are arranged with the antenna elements and transmission feed lines to, when selectively closed, electrically couple selected ones of the antenna elements and transmission feed lines to one another to generate an antenna configuration selected from a plurality of antenna configurations. A non-volatile memory is configured to store data representing at least some of the plurality of antenna configurations. A control arrangement operatively coupled to the plurality of switching elements and configured to close selected ones of the switching elements as a function of the data stored in said memory. Means are provided to selectively update the data on a function of previously selected antenna configurations.

Description:
FIELD OF THE INVENTION 
       [0001]    This disclosure relates generally to wireless communication systems. More particularly, this disclosure relates to smart antennas including self-structuring antenna subsystems and self-structuring feeds operating in different beam modes. 
       BACKGROUND OF THE INVENTION 
       [0002]    The vast majority of vehicles currently in use incorporate vehicle communication systems for receiving or transmitting signals. For example, vehicle audio systems provide information and entertainment to many motorists daily. These audio systems typically include an AM/FM radio receiver that receives radio frequency (RF) signals. These RF signals are then processed and rendered as audio output. A vehicle communication system may incorporate other functions, including, but not limited to, wireless data and voice communications, global positioning system (GPS) functionality, and satellite-based digital audio radio services (SDARS). The vehicle communication system may also incorporate remote function access (RFA) capabilities, such as remote keyless entry, remote vehicle starting, seat adjustment, and mirror adjustment. 
         [0003]    Communication systems, including vehicle communication systems, typically employ antenna systems including one or more antennas to receive or transmit electromagnetic radiated signals. In general, such antenna systems have predetermined patterns and frequency characteristics. These predetermined characteristics are selected in view of various factors, including, for example, the ideal antenna RF design, physical antenna structure limitations, and mobile environment requirements. Because these factors often compete with each other, the resulting antenna design typically reflects a compromise. For example, an antenna system for use in an automobile or other vehicle preferably operates effectively over several frequency bands (e.g., AM, FM, television, RFA, wireless data and voice communications, GPS, and SDARS), having distinctive narrowband and broadband frequency characteristics and distinctive antenna pattern characteristics within each band. Such antenna systems also preferably are capable of operating effectively in view of the structure of the vehicle body (i.e., a large conducting structure with several aperture openings). The operating characteristics (i.e., transmitting and receiving characteristics) of such antenna systems preferably are independent of the vehicle body style, orientation, and weather conditions. To accommodate these design considerations, a conventional vehicle antenna system can use several independent antenna systems and still only marginally satisfy basic design specifications. 
         [0004]    Significant improvement in mobile antenna performance can be achieved using an antenna that can alter its RF characteristics in response to changing electrical and physical conditions. One type of antenna system that has been proposed to achieve this objective is known as a self-structuring antenna (SSA) system. An example of a conventional SSA system is disclosed in U.S. Pat. No. 6,175,723, entitled “SELF-STRUCTURING ANTENNA SYSTEM WITH A SWITCHABLE ANTENNA ARRAY AND AN OPTIMIZING CONTROLLER,” to Rothwell III (“the &#39;723 patent”). The SSA system disclosed in the &#39;723 patent employs antenna elements that can be electrically connected to one another via a series of switches to adjust the RF characteristics of the SSA system as a function of the communication application or applications and the operating environment. A feedback signal provides an indication of antenna performance and is provided to a control system, such as a microcontroller or microcomputer that selectively opens and closes the switches. The control system is programmed to selectively open and close the switches in such a way as to improve antenna optimization and performance. 
         [0005]    Conventional SSA systems may employ several switches in a multitude of possible configurations or states. For example, an SSA system that has 24 switches, each of which can be placed in an open state or a closed state, can assume any of 16,777,216 (2 24 ) configurations or states. Assuming that selecting a potential switch state, setting the selected switch state, and evaluating the performance of the SSA using the set switch state each takes 1 ms, the total time to investigate all 16,777,216 configurations to select an optimal configuration is 50,331.6 seconds, or approximately 13.98 hours. During this time, the SSA system loses acceptable signal reception. 
         [0006]    The search time associated with selecting a switch configuration may be improved by limiting the number of configurations that may be selected. For example, if the control system only evaluates 0.001% of the possible switch configurations, the search time can be reduced to slightly less than a second. Laboratory experiments have demonstrated that search times can be made significantly shorter. Nevertheless, the loss of acceptable signal reception every time an SSA system is tuned to a new station, channel, or band is still a significant problem. 
         [0007]    Still, known SSA technology is limited to a basic configuration that uses a single point feed system connected to a single port antenna template having a large number of switches. This restriction has a negative impact on its potential performance and flexibility for many applications. 
         [0008]    Still, known SSA technology does not provide a roadmap for generating multiple beams over a relatively narrow frequency band (which most of today&#39;s consumer wireless and machine-to-machine communication applications require) without sacrificing antenna efficiency. 
         [0009]    In wireless communication systems, portable or mobile subscriber units communicate with a centrally located base station within a cell. The wireless communication system systems may be called a CDMA2000, GSM or WLAN communication system, for example. The subscriber units are provided with wireless data and/or voice services by the system operator and can connect devices such as, laptop computers, personal digital assistants (PDA&#39;s), cellular telephones or the like through the base station network. 
         [0010]    Each subscriber unit is equipped with an antenna. To increase the communications range between the base station and the mobile subscriber units, and for also increasing network throughput, smart antennas may be used. Smart antennas may also be used with access points and client stations in WLAN communication systems. A smart antenna includes a switched beam antenna or a phased array antenna, for example, and generates directional antenna beams. 
         [0011]    A switched beam antenna includes an active antenna element and one or more passive antenna elements. Each passive antenna element is connected to a respective impedance load by a corresponding switch. By selectively switching the passive antenna elements to their impedance load, a desired antenna pattern is generated. When a passive antenna element is connected to an inductive load, radio frequency (RF) energy is reflected back from the passive antenna element towards the active antenna element. When a passive antenna element is connected to a capacitive load, RF energy is directed toward the passive antenna element away from the active antenna element. A switch control and driver circuit provides logic control signals to each of the respective switches. 
         [0012]    For a switched beam antenna comprising an active antenna element and two passive antenna elements, for example, there are four different switching combinations for selecting a desired antenna beam if the switch is a single pole double throw (SPDT). Each switching combination corresponds to a different antenna beam mode, and consequently, the input impedance to the active antenna element changes between the different modes. The efficiency of the smart antenna varies as the input impedance varies. 
         [0013]    Similarly, in a phased array antenna, when the relative phases fed to the respective antenna elements are changed, the input impedances also vary. The phase changes are integral to the beam scanning and adaptive beam forming of a phased array antenna. This makes it difficult to match the input impedances of the various modes. To obtain a reasonable match for required beam shapes and positions, dynamic matching circuits are often used, which further add to the complexity and cost of a phased array antenna. 
       SUMMARY OF THE INVENTION 
       [0014]    Therefore, it is an object of the present invention to provide a new, simplified antenna that produces a narrow beam of reception (or transmission) pattern over a variety of possible look angle segments. 
         [0015]    In the preferred embodiments of the invention, a cognitive or smart antenna structure is provided which senses the environment and provides means for controlling the particular angular sector over which the narrow beam is formed and, at the same time, maintains power efficiency, resulting in a high gain antenna. Each “narrow beam” is narrower in angular span with higher gain compared to a half-wavelength resonant antenna. Prior cognitive antennas, known as self-structuring antennas (SSA), upon which the present invention builds, provide a “general” or formative concept of creating apertures out of sub-resonant” antenna elements inter-connected via RF switches to maximize received/transmitted signal strength without regard to antenna power efficiency. Prior SSA&#39;s also typically describe wide-band operation and do not address narrow-band features. 
         [0016]    The present invention is unique in that it addresses a method of achieving an adaptive high-gain, multi-beam antenna over a relatively narrow frequency band using principles of cognitive antennas, provides methods of maintenance of power efficiency, and describes a systematic method of improving performance by increasing antenna size. 
         [0017]    The present invention provides a simple solution of forming a narrow beam cognitive antenna that preserves its power efficiency and operates over a narrow frequency band. This is accomplished by employing a plurality of resonant and/or sub-resonant antenna elements as well as lumped and distributed inductors and capacitors (realized via discrete components or as part of the antenna structure) that, through selective connection and disconnection actions, can form highly efficient narrow beam antennas. The present invention also provides a systematic approach to increasing the gain and the number of possible beams (or patterns) by varying the size and component count of the antenna while maintaining the narrow frequency band of operation. 
         [0018]    The solutions provided by the subject invention are based on active connecting and disconnecting of the plurality of sub-resonant antenna elements in a manner to form highly efficient narrow beam and/or polarization diversity antennas in a variety of arrangements. 
         [0019]    One approach involves engaging either resonant or sub-resonant antenna elements only to form highly efficient narrow beam antennas in one of two variations. In one variation, operating antenna elements are disposed in close proximity to each other without an electrical connection between them. In the other variation, operating antenna elements are disposed in close proximity to each other with an electrical connection among some or all of them. 
         [0020]    A second approach involves engaging a plurality of resonant and/or sub-resonant antenna elements to form highly efficient narrow beam antennas in one of two variations. In one variation, operating antenna elements are disposed in close proximity to each other without an electrical connection between them. In the other variation, operating antenna elements are disposed in close proximity to each other with an electrical connection among some or all of them. 
         [0021]    A third approach involves altering the feed-point to the antenna structure. 
         [0022]    A fourth approach involves feeding the antenna structure at multiple points through a feed network. 
         [0023]    Using this methodology, a polarization diversity narrow-band cognitive antenna can be realized by means of: 
         [0024]    (1.) Utilizing typical Self-Structuring Antenna (SSA) functions to achieve optimum signal gain through sensing the environment and providing best reception (or transmission) signal Quality; 
         [0025]    (2.) Utilizing typical Self-Structuring Feed (SSF) networks to achieve a variety of polarizations and maintain impedance match between the antenna structure and the radio receivers; 
         [0026]    (3.) Using Radio Frequency (RF) switches to create or remove a conductive path; 
         [0027]    (4.) Altering the electrical configuration of the antenna aperture by optimizing how the resonant and/or sub-resonant antenna elements are combined together; 
         [0028]    (5.) Using a plurality of various resonant and/or sub-resonant antenna structure elements which could be made of patches, slots, conductive wires, cavities, dielectrics or a combination thereof; 
         [0029]    (6.) Using a variety of lumped and distributed inductances and capacitances, either as add-on components or realized as part of the antenna structure; 
         [0030]    (7.) Using a variety of ways to redirect the electric current on the aperture or inside the antenna structure or alter the field above, under or inside the antenna structure by creating or moving conductive paths distributed throughout the antenna structure; and/or 
         [0031]    (8.) By (a.) connecting or disconnecting patch or wire elements, (b.) short-circuiting or open-circuiting slot elements, (c.) introducing conducting pins inside a cavity and having them short-circuit the cavity or leaving them standing inside the cavity. 
         [0032]    The above described method is believed to provide the best means of maintaining the antenna power efficiency to achieve higher gain while maintaining the impedance match to the feed network over the frequency band of operation. 
         [0033]    These and other features and advantages of this invention will become apparent upon reading the following specification, which, along with the drawings, describes preferred and alternative embodiments of the invention in detail. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0034]    The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
           [0035]      FIG. 1 , is a block diagram illustrating an antenna system according to an embodiment; 
           [0036]      FIG. 2 , is a block diagram illustrating a communication system according to an embodiment; 
           [0037]      FIG. 3 , is a flow diagram illustrating a method to configure an antenna system according to an embodiment; 
           [0038]      FIG. 4 , is a block diagram illustrating a communication system according to an embodiment; 
           [0039]      FIG. 5 , is a block diagram illustrating a communication system according to an embodiment; 
           [0040]      FIG. 6 , is a block diagram illustrating an antenna made up of several antenna and other circuit elements setup with a reconfigurable feed network, wherein both sections contain switches for structuring purposes; 
           [0041]      FIG. 7 , is a block diagram of an antenna assembly containing resonant and sub-resonant antenna elements; 
           [0042]      FIG. 7   a , is a portion of the antenna assembly of  FIG. 7 , on an enlarged scale, illustrating multiple conductive paths between resonant and sub-resonant antenna elements including RF switches, inductors and capacitors; 
           [0043]      FIG. 8 , is a block diagram of an antenna assembly illustrating the connection of resonant antenna elements, wherein the arrangement of a central resonant element and surrounding four resonant elements (in this case) are interconnected by conductive paths that may contain an inductor or capacitor and RF switches; 
           [0044]      FIG. 9 , is a block diagram illustrating slot elements etched on the metal for control of resonant frequency and size reduction of the overall antenna; 
           [0045]      FIG. 10 , is a plan view of a patch antenna element containing multiple shorting pins, inductors and/or capacitors and RF switches located in the cavity of the patch antenna element of an antenna assembly; 
           [0046]      FIG. 11 , is a cross-sectional view of the patch antenna element of  FIG. 10 ; 
           [0047]      FIG. 11   a , is, is a portion of the antenna assembly of  FIGS. 10 and 11 , on an enlarged scale, illustrating a single conductive path between the patch antenna element and a ground plane including RF switches, inductors and capacitors; 
           [0048]      FIG. 12 , is a block diagram illustrating a polarization diversity of the antenna provided by SSF with two feeds having perpendicular locations with an RF input and switch; 
           [0049]      FIG. 13 , is a block diagram illustrating sub-resonant antenna elements similar to that of  FIG. 7  wherein the antenna radiation pattern is steered to different directions by various combinations of switch states; 
           [0050]      FIG. 14 , is a depiction of multiple beams extending in multiple directions resulting from operation of the multi-beam antenna of  FIG. 13 ; 
           [0051]      FIG. 15 , is a block diagram illustrating an antenna assembly having a multiplicity of connecting resonant and/or sub-resonant elements that feature different directions of the antenna pattern based on a various combinations of switch states; and 
           [0052]      FIG. 16 , is a depiction of multiple narrow beams extending in multiple directions resulting from operation of the multi-beam antenna of  FIG. 15 . 
       
    
    
       [0053]    Although the drawings represent embodiments of the present invention, the drawings are not necessarily to scale and certain features may be exaggerated in order to illustrate and explain the present invention. The exemplification set forth herein illustrates an embodiment of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
       DETAILED DESCRIPTION 
       [0054]    Technological advances in radio-frequency (RF) front-ends, such as reconfigurable antenna arrays, afford a new “hardware” dimension for dynamic spectrum access in cognitive wireless networks. 
         [0055]    A smart antenna system is able to provide, if compared with existing technologies, higher system capacity, improved quality of service, suppress interferences, improved power consumption and higher frequency reuse. From a practical point of view, a smart antenna system combines an antenna array with digital signal processing techniques (adaptive beamforming techniques, direction of arrival procedures, etc.) in order to obtain a software steerable antenna pattern and direct the radiated power in (or receive from) the desired direction only. 
         [0056]    A cognitive antenna is substantially an antenna array able to provide a spatial-temporal scanning of the radio environment, and it is able to reconfigure itself in order to perform optimized communication capabilities. 
         [0057]    Referring to  FIG. 1 , a self-structuring antenna (SSA) system is shown generally at  100  according to an embodiment. Antenna elements  102  are arranged with switching elements  104  in any desirable pattern, such as the illustrated pattern depicted in  FIG. 1 . It will be appreciated that the antenna elements  102  and the switching elements  104  can be arranged in patterns other than the exemplary pattern depicted in  FIG. 1 . Such patterns can be designed for acceptable performance under certain operating conditions. 
         [0058]    As illustrated, the antenna elements  102  are depicted as solid line segments, and can be implemented in practice, for example, by wires or other conductors, including but not limited to conductive traces. Alternatively, patches or other radiating devices may also be used to implement one or more of the antenna elements  102 . 
         [0059]    The switching elements  104 , which are shown generally as rectangles in  FIG. 1 , are controllably placed in an open state or a closed state via application of an appropriate control voltage or control signal. The switching elements  104  may be implemented in practice by using bipolar junction transistors (BJTs) controlled by applying an appropriate base voltage. Alternatively, the switching elements  104  may be implemented using field-effect transistors (FETs) controlled by applying an appropriate gate voltage. In yet another embodiment, the switching elements  104  may also be implemented using a combination of BJTs, FETs, integrated circuits (ICs), and the like. Even further, in another embodiment, the switching elements  104  can be implemented using mechanical devices, such as relays or miniature electromechanical system (MEMS) switches. For purposes of clarity, control terminals and control lines connected to individual switching elements  104  are not illustrated. 
         [0060]    Closing a switching element  104  establishes an electrical connection between any antenna elements  102  to which the switching element  104  is connected. Opening a switching element  104  disconnects the antenna elements  102  to which the switching element  104  is connected. Accordingly, by closing some switching elements  104  and opening other switching elements  104 , various antenna elements  102  can be selectively connected to form different configurations. Selecting which switching elements  104  are closed enables the antenna system  100  to implement a wide variety of different antenna shapes, including but not limited to loops, dipoles, stubs, or the like. The antenna elements  102  need not be electrically connected to other antenna elements  102  to affect the performance of the antenna system  100 , rather, each antenna element  102  forms part of the antenna system  100  regardless of whether the antenna element  102  is electrically connected to adjacent antenna elements  102 . 
         [0061]    A control arrangement, which is shown generally at  106 , selects particular switching elements  104  to be opened or closed to form a selected antenna configuration. The control arrangement  106  is operatively coupled to the switching elements  104  via control lines (e.g., a control bus  108 ). The control arrangement  106  may incorporate, for example, a switch controller module and a processor, which is seen generally at  130  and  142 , respectively in  FIG. 2 . 
         [0062]    To select particular switching elements  104  to be opened or closed, the control arrangement  106  selects an antenna configuration. When the antenna system  100  is first activated, the control arrangement  106  searches the conceptual space of possible antenna configurations to identify an antenna configuration that will produce acceptable antenna performance under the prevailing operating conditions. To increase the speed of the search process, a memory  110  stores antenna configurations (e.g., switch states that are expected to produce acceptable antenna performance). 
         [0063]    The memory  110  is operatively coupled to the control arrangement  106 , for example, via an address bus  112  and a data bus  114 . The memory  110  may be implemented using any of a variety of conventional memory devices, including, but not limited to, random access memory (RAM) devices, static random access memory (SRAM) devices, dynamic random access memory (DRAM) devices, non-volatile random access memory (NVRAM) devices, and non-volatile programmable memories, such as, for example, programmable read only memory (PROM) devices and electronically-erasable programmable read only memory (EEPROM) devices. The memory  110  may also be implemented using a magnetic disk device or other data storage medium. 
         [0064]    The memory  110  can store the antenna configurations or switch states using any of a variety of representations. In some embodiments, each switching element  104  may be represented by a bit having a value of “1” if the switching element  104  is open or a value of “0” if the switching element  104  is closed in a particular antenna configuration. Accordingly, each antenna configuration is stored as a binary word having a number of bits equal to the number of switching elements  104  in the antenna system  100 . The example antenna system  100  illustrated in  FIG. 1  includes seventeen switching elements  104 ; therefore, according to the illustrated embodiment, each antenna configuration would be represented as a 17-bit binary word. 
         [0065]    In some embodiments, multiple switching elements  104  may be controlled to assume the same open or closed state as a group. For example, as the antenna system  100  develops usage history, the control arrangement  106  may determine that performance benefits may result when certain groups of antenna elements  102  are electrically connected or disconnected. Alternatively, the determination to control such switching elements  104  as a group may be made at the time of manufacture of the antenna system  100 . For example, certain zones formed by groups of antenna elements  102  may be controlled as a group for different frequency bands. When multiple switching elements  104  are controlled as a group, smaller binary words can represent antenna configurations or switch states. This more compact representation may yield certain benefits, particularly when the determination to control switching elements  104  as a group is made at the time of manufacture. In this case, the memory  110  may be implemented using a device having less storage capacity, potentially resulting in decreased manufacturing costs. 
         [0066]    As the antenna system  100  is used, the control arrangement  106  updates the memory  110  to improve subsequent iterations of the search process. The control arrangement  106  causes the memory  110  to store binary words that represent the switch states for antenna configurations that are determined to produce acceptable antenna characteristics. Accordingly, when the control arrangement  106  repeats the search process (e.g., when the antenna system  100  is reactivated after having been deactivated), the search process can begin at an antenna configuration that is known to produce acceptable results. In conventional antenna systems lacking a memory  110 , historical information is lost after each iteration of the search process (i.e., every time the communication system is turned off or tuned to a different communication band). Accordingly, in such conventional antenna systems, the search process begins anew with each iteration. By contrast, storing and using historical information relating to previous iterations of the search process can improve the speed of the search process. 
         [0067]    The control arrangement  106  may read or update the memory  110  based on a control signal provided by a receiver  116 , for example, when the communication system is activated. This control signal may be, for example, a received signal strength indicator (RSSI) signal generated as a function of an RF signal received by the receiver  116 . Alternatively, the control signal may be generated as a function of an operational mode of the antenna system  100  (e.g., whether the antenna system  100  is to be configured to receive an AM or FM signal, a UHF or VHF television signal, a remote function access (RFA) signal, a global positioning system (GPS) signal, an SDARS signal, or a wireless data and voice communications signal, such as a CDMA or GSM signal. The control signal may also be generated as a function of the particular frequency or frequency band to which the receiver  116  is tuned. 
         [0068]    When the control arrangement  106  receives the control signal from the receiver  116 , the control arrangement  106  initiates the search process to select an antenna configuration in response to the control signal. The control arrangement  106  then addresses the memory  110  via the address bus  112  to access the binary word stored in the memory  110  that corresponds to the selected antenna configuration. The control arrangement  106  receives the binary word via the data bus  114 , and, based on the binary word, outputs appropriate switch control signals to the switching elements  104  via the control bus  108 . The switch control signals selectively open or close the switching elements  104  as appropriate. 
         [0069]      FIG. 2  shows a communication system generally at  120  according to another embodiment. According to one possible implementation, the communication system  120  may be installed in a vehicle, such as, for example, an automobile, boat, train, or the like. Alternatively, the communication system  120  may be implemented as a standalone unit, e.g., a portable entertainment system, such as a walkman, boombox, or the like. A receiver  122  receives a radiated electromagnetic signal, such as an RF signal, via an antenna  124 . Depending on the particular application, the radiated electromagnetic signal can be of any of a variety of types, including but not limited to an AM or FM radio signal, a UHF or VHF television signal, an RFA signal, a GPS signal, an SDARS signal, or a wireless data and voice communications signal, such as, for example, a CDMA or GSM signal. 
         [0070]    The antenna  124  includes antenna elements and switching elements, which are shown generally at  126  and  128 , respectively. As illustrated, the antenna and switching elements  126 ,  128  operate and are arranged in a similar manner as that shown and described above in  FIG. 1 . A switch controller  130  provides control signals to the switching elements  128  to selectively open or close the switching elements  128  to implement particular antenna configurations. The switch controller  130  is operatively coupled to the switching elements  128  via control lines  132 . 
         [0071]    The switch controller  130  is also operatively coupled to a memory  134 , for example, via a bus  136 . The memory  134  stores antenna configurations or switch states and is addressable using one or more lines  138 ,  140  extending from the processor  142  and receiver  122 , respectively. It should be noted that the memory  134  need not store all possible antenna configurations or switch states. For many applications, it would be sufficient for the memory  134  to store up to a few hundred of the possible antenna configurations or switch states. Accordingly, any of a variety of conventional memory devices may implement the memory  134 , including, but not limited to, RAM devices, SRAM devices, DRAM devices, NVRAM devices, and non-volatile programmable memories, such as PROM devices and EEPROM devices. The memory  134  may also be implemented using a magnetic disk device or other data storage medium. 
         [0072]    As similarly described above, the memory  134  can store the antenna configurations or switch states using any of a variety of representations. In some embodiments, each switching element  128  may be represented by a bit having a value of “1” if the switching element  128  is open or a value of “0” if the switching element  128  is closed in a particular antenna configuration. Accordingly, each antenna configuration is stored as a binary word having a number of bits equal to the number of switching elements  128  in the antenna  124 . 
         [0073]    In operation, the processor  142  selects an antenna configuration appropriate to the operational state of the communication system  120  (i.e., the type of radiated electromagnetic signal received by the receiver  122  or the particular frequency or frequency band in which the communication system  120  is operating). For example, the receiver  122  may provide a control signal to the processor  142  or the memory  134  that indicates the operational mode of the antenna  124 , e.g., whether the antenna  124  is to be configured to receive an AM, FM, UHF, VHF, RFA, CDMA, GSM, GPS, or SDARS signal. The receiver  122  may also generate the control signal as a function of the particular frequency or frequency band to which the receiver  122  is tuned. The control signal may also indicate certain strength or directional characteristics of the radiated electromagnetic signal. For example, the receiver  122  may provide a received signal strength indicator (RSSI) signal to the processor  142 . 
         [0074]    The processor  142  responds to the control signal by initiating a search process of the conceptual space of possible antenna configurations to select an appropriate antenna configuration. Rather than beginning at a randomly selected antenna configuration each time the search process is initiated, the processor  142  starts the search process at a switch configuration that is known to have produced acceptable antenna characteristics under the prevailing operating conditions at some point during the usage history of the communication system  120 . For example, the processor  142  may address the memory  134  to retrieve a default switch configuration for a given operating frequency. If the default configuration produces acceptable antenna characteristics, the processor  142  uses the default switch configuration. On the other hand, if the default switch configuration no longer produces acceptable antenna characteristics, the processor  142  searches for a new switch configuration using the default switch configuration as a starting point. Once the processor  142  finds the new switch configuration, the processor  142  updates the memory  134  via the lines  138  to replace the default switch configuration with the new switch configuration. 
         [0075]    Regardless of whether the processor  142  selects the default switch configuration or another switch configuration, the processor  142  indicates the selected switch configuration to the switch controller  130  via lines  144 . The switch controller  130  then addresses the memory  134  via the bus  136  to access the binary word stored in the memory  134  that corresponds to the selected antenna configuration. The switch controller  130  receives the binary word via the bus  136 , and, based on the binary word, outputs appropriate switch control signals to the switching elements  128  via the control lines  132 . The switch control signals selectively opens or closes the switching elements  128  as appropriate, thereby forming the selected antenna configuration. 
         [0076]    The processor  142  is typically configured to operate with one or more types of processor readable media, such as a read-only memory (ROM) device, which is shown generally at  146 . Processor readable media can be any available media that can be accessed by the processor  142  and includes both volatile media, nonvolatile media, removable media, and non-removable media. By way of example, and not limitation, processor readable media may include storage media and communication media. Storage media includes both volatile, nonvolatile, removable, and non-removable media implemented in any method or technology for storage of information, such as, for example, processor-readable instructions, data structures, program modules, or other data. Storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory, CD-ROM, digital video discs (DVDs), magnetic cassettes, magnetic tape, magnetic disk storage, or any other medium that can be used to store any desired information that can be accessed by the processor  142 . Communication media typically embodies processor-readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transport mechanism including any information delivery media. The term “modulated data signal” means a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, communication media includes wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, RF, infrared, and other wireless media. Combinations of any of the above are also intended to be included within the scope of processor-readable media. 
         [0077]      FIG. 3  is a flow diagram illustrating an example method for configuring the antenna  124 , according to another embodiment. The method may be performed, for example, in accordance with processor-readable instructions stored in the ROM  146 . First, the processor  142  receives a control signal at step  150  from the receiver  122 . As described above in connection with  FIG. 2 , the control signal may indicate the operational mode of the antenna  124  (e.g., the particular frequency or frequency band to which the receiver  122  is tuned). Alternatively, the control signal may indicate the impedance of the antenna  124 . The control signal may also be an RSSI signal or other signal indicating certain strength or directional characteristics of the radiated electromagnetic signal. In addition, the control signal may be generated by a remote receiver other than the receiver  122 , for example, to enable improved reception at the remote receiver. 
         [0078]    In response to the control signal, the processor  142  selects an appropriate antenna configuration. Specifically, the processor  142  accesses the memory  134  to retrieve a recent antenna configuration at step  152 , such as a default antenna configuration, that has produced or is expected to produce acceptable antenna characteristics in the current operational mode (e.g., for the current operating frequency or frequency band). The processor  142  then configures the switching elements  128  to produce the antenna configuration at step  154  by controlling the memory  134  to output data representing the antenna configuration. Based on this data, the switch controller  130  drives each switching element  128  to an open state or a closed state, as appropriate. The processor  142  evaluates the performance of the selected antenna configuration, for example, using an RSSI or other feedback signal provided by the receiver  122 . If the selected antenna configuration produces acceptable antenna characteristics, the processor  142  uses that antenna configuration. On the other hand, if the selected antenna configuration does not produce acceptable antenna characteristics, the processor  142  selects a different antenna configuration at step  156 . The processor  142  addresses, at step  158 , the memory  134  and retrieves data representing the newly selected antenna configuration at step  160 . Next, the processor  142  configures the switching elements  128  to produce the newly selected antenna configuration at step  154  and again evaluates the performance of the antenna configuration. 
         [0079]    When the processor  142  identifies an antenna configuration that produces acceptable antenna characteristics, the processor  142  uses that antenna configuration. In addition, the processor  142  updates the memory  134  to replace the previously stored antenna configuration with the new antenna configuration at step  162 . In this way, the communication system  120  adapts to changing environmental conditions, as well as changing conditions relating to the antenna  124  itself. For example, as the communication system  120  ages, certain antenna elements  126  or switching elements  128  may exhibit declining performance or stop functioning entirely. Accordingly, certain switch configurations that once produced acceptable antenna characteristics may no longer work as well. By updating the memory  134 , such switch configurations can be eliminated from further consideration. 
         [0080]    Referring to  FIG. 4 , a communication system is shown generally at  220  according to an embodiment including the self-structuring antenna  124 . Self-structuring feed (SSF) ports or switches  250   a - 250   g  selectively interconnect the antenna  124  and a signal feed circuit in the form of a multiple feed template  252 , a receiver  222  receives signals from the signal feed circuit  252 , an SSF processor  242  receives an output signal from the receiver  222 , an SSF switch controller  230  receives an output signal from the SSF processor  242 , and control lines  232  interconnect the SSF controller  230  and switches  250   a - 250   g.    
         [0081]    The self-structure feed switches  250   a - 250   g  may selectively interconnect the antenna  124  and signal feed circuit  252  at respective spaced apart locations along a perimeter of the antenna  124 . However, switches  250   a - 250   g  may be disposed at any location between the antenna  124  and the signal feed circuit  252 . Moreover, although seven switches  250   a - 250   g  are shown, it will be appreciated that any desirable number of switches  250   a - 250   g  may be included. 
         [0082]    In operation, each of the SSF feed switches  250   a - 250   g  may be independently actuated by the controller  230  between a first position in which the antenna  124  and signal feed circuit  252  are in communication though (a) switch(s)  250   a - 250   g  and a second position in which the antenna  124  and signal feed circuit  252  are not in communication through the switch(s)  250   a - 250   g . Switches  250   a - 250   g  may function as a performance-adjusting device for improving the signal reception and/or signal transmission performance of the antenna  124 . In one embodiment, the SSF switch controller  230  and SSF processor  242  control switches  250   a - 250   g  are dependent upon the signal received by the receiver  222  via the antenna  124 . 
         [0083]    The switches  250   a - 250   g  may begin in various combinations of the first and second positions when the antenna  124  passes a received signal to the receiver  222  via the switches  250   a - 250   g  and switch feed circuit  252 . The SSF processor  242  may analyze an output signal from the receiver  222  to determine signal strength, signal-to-noise ratio, and/or some other attribute of the signal passed to the receiver  222 . The SSF memory  234  may receive an analysis signal from the SSF processor  242  to record the performance of the antenna  124 , as represented by the analysis and the position of the switches  250   a - 250   g  that produced that particular performance. The SSF switch controller  230  may then actuate at least one of the switches  250   a - 250   g  between the first and second positions to thereby provide an antenna arrangement with a different level of performance. The SSF memory  234  may again record the switch positions and the corresponding antenna performance produced thereby. The process may continue with the SSF switch controller  230  changing and recording switch positions and the resulting performance until the SSF processor  242  has determined a combination of switch positions that produces an optimal, favorable, or at least acceptable antenna performance. 
         [0084]    The SSF processor  242  may try every possible combination of switch positions during the above process. Alternatively, the SSF processor  242  may only sample a number of combinations of switch positions and pick the best combination of the number sampled. As another alternative, the SSF switch controller  230  and processor  242  may include intelligence, which is shown generally at  234  and  246 , respectively that enables the SSF switch controller  230  and processor  242  to systematically select particular switch combinations that are likely to yield good performance. The switch combinations may be selected, for example, based upon recognized patterns in the performance of previously selected combinations of switch positions. 
         [0085]    Accordingly, the SSF switch controller  230  memory  234  may include an operational database for storing the best combination of switch positions for each of a list of possible operating conditions. Experimentation or trials to determine the best switch combinations may occur in the factory, in the field, and/or may be ongoing over the operational life of the antenna system. 
         [0086]    Referring to  FIG. 5 , a communication system is shown generally at  320  according to an embodiment including the self-structuring antenna  124 . The communication system  320  includes switchable, self-structuring variable impedance elements (SSVIE)  350   a - 350   h  for selectively adding a variable impedance load to the antenna  124  and/or to a signal feed circuit  352 . The elements  350   a - 350   h  are connected to the antenna  124  and signal feed circuit  352  and be may be used for impedance matching. A switchable capacitive load is seen at  350   a ,  350   e . A switchable inductive load is seen at  350   b ,  350   f . Switchable resistive loads are seen at  350   c ,  350   g . Switchable capacitive, inductive, and/or resistive loads are seen at  350   d ,  350   h . Any or all of the elements  350   a - 350   d  may be selectively connected in parallel and/or series with the signal feed circuit  352 . Similarly, any or all of elements  350   e - 350   h  may be selectively connected in parallel and/or series with the antenna  124 . Each of the elements  350   a - 350   h  has a respective switch device that may be actuated to thereby connect or disconnect the element  350   a - 350   h  to/from the antenna  124  and antenna feed circuit  352 . 
         [0087]    As illustrated, a receiver  322  receives signals from the signal feed circuit  352 . An SSVIE processor  342  receives an output signal from the receiver  322 . An SSVIE switch controller  330  receives an output signal from the SSVIE processor  342 , and control lines  332  interconnect the SSVIE switch controller  330  and the switch devices of the elements  350   a - 350   h . The elements  350   a - 350   h  may all have different impedance values, including different capacitances and different inductances. In one embodiment, the elements  350   a - 350   h  are sections of coaxial cable having different lengths and therefore, different impedances, i.e., different capacitances, inductances, and resistances. Generally, the SSVIE switch controller  330  control the elements  350   a - 350   h  dependent upon a signal received by the receiver  322  via the antenna  124 . The SSVIE controller  330  and processor  342  may open and close the switch devices of the elements  350   a - 350   h  in different combinations and then determine which of the combinations results in the best antenna performance. As another alternative, the SSVIE switch controller  330  and processor  342  may include intelligence, which is shown generally at  334  and  346 , respectively that enables the SSVIE switch controller  330  and processor  342  to systematically select particular element combinations that are likely to yield good performance. 
         [0088]    As demonstrated by the foregoing discussion, various embodiments may provide certain advantages. For instance, using the stored antenna configurations as a starting point for the process of searching for an antenna configuration that produces acceptable antenna characteristics under particular operating conditions may reduce the search time. In view of the improvements shown in  FIGS. 1-5 , performance of the SSA may be improved further by arraying self-structuring feed (SSF) and self-structuring variable impedance element (SSVIE) subsystems with the SSA. Referring now to  FIG. 6 , a communication system is shown generally at  420  according to an embodiment. The communication system  420  generally includes the same elements as the communication systems  120 ,  220 ,  320  shown in  FIGS. 2 ,  4 , and  5  with the exception that the communication system  420  includes one or more arrayed processors  422   a - 422   c  and switch controllers  430   a - 430   c . Although the processors  422   a - 422   c  and switch controllers  430   a - 430   c  are shown in an arrayed pattern that are each respectively separated into three blocks for purposes of clarity in illustrating the concept, it will be appreciated that the function of each block shown at  422   a - 422   c  and  430   a - 430   c  may be incorporated into a single processor and switch controller, respectively, as suggested in  FIGS. 2 ,  4 , and  5 . 
         [0089]    The communication system  420  generally utilizes the concept of using a combination of the SSA, SSF, and SSVIE techniques shown in  FIGS. 2 ,  4 , and  5 . According to an embodiment, the communication system  420  may be implemented for use as an AM/FM rear window glass antenna system in a vehicle, which is described in U.S. Pat. No. 7,558,555 B2 to L. Nagy, the specification of which is incorporated herein by reference. The communication system  420  uses various self-structuring techniques as sub-systems that form an aggregates system that uses the best of each SSA, SSF, and SSVIE sub-system, or, a combination of the sub-systems to obtain an optimum antenna solution for its application, for example to a rear window glass antenna system  500  of a vehicle, and its operating environment. 
         [0090]    Referring to  FIG. 6 , a general set-up of an antenna system  610  is illustrated. Antenna system  610  includes a reconfigurable antenna  612  and a reconfigurable feed network  614  interconnected thereto through multiple, spaced-apart feeding locations  616 ,  618  and  620 . The reconfigurable antenna  612  can contain various types of resonating elements such as patch elements  622 , slot elements  624 , wire elements  626 , cavities  628  dielectrics  630 , radio frequency (RF) switches (mechanical, solid state, MEMS)  632 , inductors  634 , capacitors  636  and shorting pins  638 . Both the SSA  612  and reconfigurable feed  614  contain RF switches  632  for structuring purposes. 
         [0091]    Referring to  FIGS. 7 and 7   a , an alternative embodiment reconfigurable antenna system  640  includes a central resonant element  642  peripherally enclosed by four sub-resonant elements  644 . Adjacent portions of the resonant element  642  are interconnected with each of the sub-resonant elements  644  via multiple enlarged conductive paths  646  which contain an RF switch  648  in series with an element  650  such as a conductor, capacitor or inductor. 
         [0092]    Referring to  FIG. 8 , another alternative embodiment reconfigurable antenna system  652  includes a central resonant element  654  peripherally enclosed by four additional resonant elements  656 . Adjacent portions of the resonant elements  654  and  656  are interconnected via multiple enlarged conductive paths  658  which contain an RF switch in series with an element such as a conductor, capacitor or inductor as described in connection with  FIGS. 7 and 7   a.    
         [0093]    Referring to  FIG. 9 , another alternative embodiment reconfigurable antenna system  660  including a metallic antenna element  662  with several slot elements  664 ,  666  and  668  of varying sizes formed therein for control of resonant frequency and effecting size reduction of the antenna  660 . 
         [0094]    Referring to  FIGS. 10 ,  11  and  11   a , another alternative embodiment reconfigurable antenna system  670  including a patch antenna element  672  is interconnected to a ground plane  674  via several spaced-apart shorting pins  676 , each in the form of inductors and/or capacitors  678  and RF switches  680 . 
         [0095]    Referring to  FIG. 12 , another alternative embodiment reconfigurable antenna system  682  provides polarization diversity through two feeds  684  and  686  at mutually perpendicular locations of an antenna element  688 . An RF input  690  is selectively interconnected through an RF switch  692  for selection of the polarization of the reconfigurable antenna  682 . 
         [0096]    Referring to  FIGS. 13 and 14 , the reconfigurable antenna system  640  of  FIGS. 7 and 7   a  having resonant and sub-resonant elements  642  and  644  is controlled to achieve directionality of the resulting antenna reception/transmission patterns  694 ,  696  and  698  along different axes  700 ,  702  and  704  (by way of example) based on various combinations of RF switch  648  states. 
         [0097]    Referring to  FIGS. 15 and 16 , another alternative embodiment reconfigurable antenna system  706  provides a single, central resonant element  708  surrounded by an array of a number of resonant and/or sub-resonant elements  710 . The reconfigurable antenna system  706  is controlled to achieve directionality of the resulting antenna reception/transmission patterns  718 ,  720  and  722  along different axes  724 ,  726  and  728  (by way of example) based on various combinations of RF switch  724  states. 
         [0098]    While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit. It is to be understood that the invention has been described with reference to specific embodiments and variations to provide the features and advantages previously described and that the embodiments are susceptible of modification as will be apparent to those skilled in the art. 
         [0099]    Furthermore, it is contemplated that many alternative, common inexpensive materials can be employed to construct the basis constituent components. Accordingly, the forgoing is not to be construed in a limiting sense. 
         [0100]    The invention has been described in an illustrative manner, and it is to be understood that the terminology, which has been used is intended to be in the nature of words of description rather than of limitation. 
         [0101]    Obviously, many modifications and variations of the present invention are possible in light of the above teachings. For example, . . . It is, therefore, to be understood that within the scope of the appended claims, wherein reference numerals are merely for illustrative purposes and convenience and are not in any way limiting, the invention, which is defined by the following claims as interpreted according to the principles of patent law, including the Doctrine of Equivalents, may be practiced otherwise than is specifically described.