Abstract:
A system, in some embodiments, comprises: a processor; a transceiver coupled to the processor; and an antenna including a central element that connects to one or more of the processor and the transceiver, said antenna further including multiple coupling elements that electromagnetically couple to the central element, wherein each of the multiple coupling elements comprises a separate variable capacitor.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application claims priority to U.S. Provisional Application No. 62/255,617, filed on Nov. 16, 2015, entitled “TUNABLE ANTENNA FOR HIGH-EFFICIENCY, WIDEBAND FREQUENCY COVERAGE,” invented by Mohammad-Reza NEZHAD-AHMADI and Andrew KUIKMAN, and is incorporated herein by reference and priority thereto for common subject matter is hereby claimed. 
     
    
     BACKGROUND 
       [0002]    Many wireless devices are designed to operate in multiple frequency bands, thus increasing the versatility of such devices in different operating environments. For example, some so-called multi-band cell phones can operate in the 700-960 MHz, 1700-220 MHz and 2500-2700 MHz frequency bands, making such phones well-suited for travel between countries in which different communication standards are used. Wireless medical devices also may operate in different bands (e.g., 400 MHz, 900 MHz and 2.4 GHz bands). One drawback to such devices, however, is that an increased number of frequency bands causes impedance mismatches that ultimately result in poorer operational efficiency within each of those frequency bands. Compounding such inefficiency is the reduced power transfer that occurs between transceivers and antennas when antenna impedance varies due to environmental changes (e.g., by holding a cell phone near the head, by mounting a wireless medical device on or near a human body). 
       SUMMARY 
       [0003]    At least some of the embodiments disclosed herein are directed to a system, comprising: a processor; a transceiver coupled to the processor; and an antenna including a central element that connects to one or more of the processor and the transceiver, said antenna further including multiple coupling elements that electromagnetically couple to the central element, wherein each of the multiple coupling elements comprises a separate variable capacitor. These embodiments may be supplemented using one or more of the following concepts, in any order and in any combination: wherein a change in the capacitances of the variable capacitors causes a shift in the frequencies at which the system operates most efficiently; wherein at least one of the multiple coupling elements comprises a ground connection positioned within one centimeter of at least one of said variable capacitors; wherein said separate variable capacitors are controlled by control signals supplied by the processor; wherein a capacitance range of at least one of said variable capacitors is 2.05 pico Farads to 8.2 pico Farads; wherein a control signal applied to at least one of said variable capacitors is determined based on a target operating frequency for the system; further comprising a data structure that cross-references multiple possible target operating frequencies for the system with multiple possible control signals that can be applied to one or more of the variable capacitors; wherein a control signal applied to at least one of said variable capacitors is determined based on a mismatch between an antenna impedance and an impedance associated with said transceiver; wherein said mismatch is detected using one or more sensors that sense environmental or positional changes associated with the system; wherein the processor uses a data structure that cross-references possible data from said one or more sensors with possible control signals that can be applied to the separate variable capacitors; further comprising a closed loop tuning module that detects said mismatch, wherein the processor uses data from the closed loop tuning module to determine said control signal to correct said mismatch; wherein the multiple coupling elements do not directly connect with the central element or with each other; wherein each of the multiple coupling elements comprises multiple variable capacitors. 
         [0004]    At least some embodiments are directed to an antenna, comprising: a central element that receives signals from and provides signals to a transceiver; multiple coupling elements that electromagnetically couple with the central element; and multiple variable capacitors, each of said capacitors positioned on a different one of the multiple coupling elements. These embodiments may be supplemented using one or more of the following concepts, in any order and in any combination: wherein each of the multiple coupling elements has a ground connection, and wherein each of said ground connections is positioned between one millimeter and one centimeter away from the variable capacitor on that coupling element; wherein the multiple coupling elements do not connect directly with the central element; wherein the multiple coupling elements are separated from each other at all points by a minimum distance that ranges from one millimeter to one centimeter, inclusive. 
         [0005]    At least some embodiments are directed to a method, comprising: determining multiple target operating frequencies in an antenna; identifying, based on the multiple target operating frequencies, control signals to apply to multiple variable capacitors built into coupling elements of said antenna; and applying the control signals to the multiple variable capacitors so that said multiple target operating frequencies are the frequencies at which the antenna operates most efficiently. These embodiments may be supplemented using one or more of the following concepts, in any order and in any combination: further comprising using data structures that cross-reference multiple possible target operating frequencies with multiple possible control signals to identify said control signals to apply to the multiple variable capacitors; further comprising applying said control signals to the multiple variable capacitors so that said frequencies at which the antenna operates most efficiently form a continuous frequency band. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]    In the drawings: 
           [0007]      FIG. 1  is a block diagram of a dual resonance antenna in accordance with embodiments of the invention. 
           [0008]      FIG. 2  is a graph illustrating efficiency in a dual resonance antenna as a function of operating frequency. 
           [0009]      FIG. 3  is a block diagram of a generic, multi-resonance antenna in accordance with embodiments of the invention. 
           [0010]      FIG. 4  is a block diagram of components usable to drive antennas in accordance with embodiments of the invention. 
           [0011]      FIG. 5A  is a flow diagram of a method in accordance with embodiments of the invention. 
           [0012]      FIG. 5B  is a flow diagram of another method in accordance with embodiments of the invention. 
       
    
    
       [0013]    It should be understood, however, that the specific embodiments given in the drawings and detailed description thereto do not limit the disclosure. On the contrary, they provide the foundation for one of ordinary skill to discern the alternative forms, equivalents, and modifications that are encompassed together with one or more of the given embodiments in the scope of the appended claims. 
       DETAILED DESCRIPTION 
       [0014]    Disclosed herein is a wireless communication system that can dynamically adjust the frequencies at which it operates most efficiently and that can dynamically adapt to changes in antenna impedance. The system includes an antenna that has a central element that is electromagnetically coupled to multiple coupling elements, and each such coupling element contains a variable capacitor. The variable capacitor can be adjusted to dynamically ensure that the antenna impedance and the transceiver impedance match, regardless of environmental or positional changes that may be affecting antenna impedance and irrespective of the frequencies at which the system is operating. 
         [0015]      FIG. 1  is a block diagram of an illustrative dual resonance antenna  100  in accordance with embodiments of the invention. The antenna  100  includes a central element  102  and coupling elements  104  and  106  to which the central element  102  electromagnetically couples. In at least some embodiments, the central element  102  does not directly connect to one or more of the coupling elements  104  and  106 , and in some embodiments, the coupling elements  104  and  106  do not directly connect to each other. In at least some embodiments, the coupling elements  104  and  106  are separated from each other at all points by a minimum distance ranging between one millimeter and one centimeter, inclusive. The central element  102  connects to a micro-coaxial (“microcoax”) cable  108  that transfers signals  110  to and from the central element  102  via a feed point  112 . As explained below, the signals  110  are provided to and from, e.g., a transceiver or processor. The central element  102  and coupling elements  104  and  106  may be formed as desired using well-known techniques and with specific geometries that accomplish specific design objectives. The coupling element  104  has a ground connection  114  and the coupling element  106  has a ground connection  116 . In at least some embodiments, the ground connections  114 ,  116  for the coupling elements  104 ,  106  are through the variable capacitors—i.e., in these embodiments, the coupling elements  104 ,  106  do not directly connect to the ground connections  114 ,  116 . The coupling elements  104  and  106  contain variable capacitors  118 ,  120 , respectively. In at least some embodiments, the variable capacitors  118  and  120  are positioned close to the ground connections  114 ,  116 . For instance, the distance between the ground connection  114  and the variable capacitor  118  may range between one millimeter and one centimeter. The scope of disclosure, however, is not limited to this or any other particular placement of the variable capacitors  118 ,  120 , so long as the variable capacitors  118 ,  120  are directly connected with the coupling elements  104 ,  106 . 
         [0016]    The variable capacitors  118 ,  120  may be any type of device whose capacitance varies based on some type of control signal. For example, the variable capacitors may vary according to the voltage applied to the capacitors. Although the specific capacitance ranges chosen for the variable capacitors  118 ,  120  may vary based on the overall design of the antenna  100  and specific performance objectives, in at least some embodiments, the capacitance range is between 2.05 pico Farads to 8.2 pico Farads, inclusive. The variable capacitors  118 ,  120  preferably, but not necessarily, are barium strontium titanate (BST) capacitors. Furthermore, they are preferably, but not necessarily, analog capacitors, since analog capacitors provide greater granularity than digital capacitors. 
         [0017]    In an illustrative, non-limiting operation, the central element  102  receives a signal  110  (e.g., from a transceiver) via feed point  112 . The central element  102  radiates the signal, and the energy of the radiated signal is at least partially absorbed by the coupling elements  104 ,  106 . The coupling elements  104 ,  106 , in turn, radiate the absorbed energy. During operation—for instance, when a user holds the electronic device containing the antenna  100  near the body or metallic objects or when the position of the electronic device is rotated—the impedance of the antenna  100  may change. This change in impedance causes a mismatch between the antenna impedance and the impedance of the transceiver to which the antenna connects. Such impedance mismatches may decrease the operating efficiency of the antenna  100  in the desired frequency band. In such instances, components—such as that described in detail with respect to  FIG. 4 , below—detect the shift in antenna impedance and alter the capacitance of one or both of the variable capacitors  118 ,  120  so that the antenna and transceiver impedances match or at least come closer to matching than before the capacitance(s) were adjusted. In this way, efficiency is improved over the impedance mismatch situation created by environmental or positional changes with respect to the antenna  100  or the electronic device containing the antenna  100 . 
         [0018]    In addition, even if there is no impedance mismatch like the type described above, the capacitances of the variable capacitors  118 ,  120  may be dynamically adjusted to change the frequencies at which the device most efficiently operates.  FIG. 2  is a graph  200  illustrating antenna efficiency in a dual resonance antenna across the 690-960 MHz frequency spectrum. The horizontal axis  202  depicts the operating frequency in MHz of the electronic device containing two illustrative, variable capacitors in accordance with embodiments of the invention. The vertical axis  204  indicates antenna efficiency in decibels (dB). Applying 2V to one of the two illustrative, variable capacitors produces an efficiency peak at approximately 703 MHz, and applying 8V to the other of the two variable capacitors produces a second efficiency peak at approximately 960 MHz. As the graph illustrates, altering the voltages applied to one or both of the variable capacitors independently shifts the efficiency peaks to differing frequency values. Thus, if a smartphone is operating at 900 MHz and 1800 MHz and it determines that it has new target operating frequencies of 703 MHz and 960 MHz (e.g., due to a change in location or some other reason), components such as that described with respect to  FIG. 4  below apply 2V and 8V to the variable capacitors, thus improving impedance matching between the antenna and the transceiver when operating at 703 MHz and 960 MHz and thus improving efficiency when operating at those target frequencies. Control signals applied to the variable capacitors may be varied to shift the efficiency peaks as desired—for example, in some situations, the variable capacitors may be adjusted so that the frequencies at which operation is most efficient are adjacent and thus form a continuous, wide frequency band. The graph  200  is merely illustrative of the operation of one or some antennas, and the scope of disclosure is not limited to any particular electronic device and/or antenna configuration that results in any particular frequency-efficiency curve(s). In addition, graph  200  shows a bar  206  that marks an ideal efficiency level for operation in at least some circumstances, but in some cases acceptable efficiency levels may be below this bar. 
         [0019]      FIG. 3  is a block diagram of a multi-resonance antenna  300  in accordance with embodiments of the invention. The antenna  300  is a more generic representation of the antenna  100  shown in  FIG. 1 . The antenna  300  comprises a central element  302 ; coupling elements  304 . 1 ,  304 . 2 , . . . ,  304 .N; a microcoax cable  306 ; a closed loop tuning module  308 ; a feed point  310 ; ground connections  312 . 1 ,  312 . 2 , . . . ,  312 .N; variable capacitors  314 . 1 ,  314 . 2 , . . . ,  314 .N; and control signal connections  316 . 1 ,  316 . 2 , . . . ,  316 .N that control the variable capacitors. In some embodiments, one or more of the coupling elements may connect to multiple variable capacitors. The operation of the antenna  300  is similar to that of antenna  100  and thus is not repeated here. The closed loop tuning module  308 , which is not specifically illustrated in the antenna  100 , operates to identify impedance mismatches between the antenna  300  and a transceiver connected to the microcoax cable  306 . The module  308  may contain, for instance, an integrated coupler and sense integrated circuit to detect such impedance mismatches on the cable  306 . 
         [0020]      FIG. 4  is a block diagram of components  400  usable to drive antennas (e.g., antennas  100 ,  300 ) in accordance with embodiments of the invention. The components  400  may be incorporated into the same electronic device as the antenna that it drives, although the scope of disclosure is not limited as such. The components  400  include a processor  401 ; a transceiver  402  that connects to the processor  401 ; storage  404  (e.g., permanent or temporary; may include, for instance, hard drives, thumb drives, optical storage, ROM, RAM, remote or distributed memory; cloud via a network connection, etc.); sensors  406  (e.g., to detect rotation of the electronic device containing the components  400 ; to detect position of the device relative to a body or body part); microcoax cable  306  (i.e., from  FIG. 3 ); optional controller  408  (e.g., a dedicated, integrated circuit for controlling one or more variable capacitors); and control signal connections  316 . 1 ,  316 . 2 , . . . ,  316 .N, which connect to and control the variable capacitors described above. 
         [0021]    In operation, signals to be transmitted via the disclosed antenna (e.g., antenna  100 ,  300 ) are generated by the processor  401  and prepared for transmission (e.g., modulation) by transceiver  402 . The modulated signal is then sent to the antenna via the microcoax cable  306 . Received signals are processed and demodulated by the transceiver  402  and the resulting electrical signal is provided to the processor  401 . The storage  404  includes one or more data structures  410  and one or more algorithms (e.g., software)  412 . At least one of the data structures  410  cross-references multiple possible target operating frequencies with multiple possible control signals (e.g., voltages) that may be applied to one or more variable capacitors on the antenna via connections  316 . 1 ,  316 . 2 , . . . ,  316 .N. The reasons that an electronic device would shift to different operating frequencies is beyond the scope of this disclosure, but if such a decision is made, the data structure may be used to determine the optimal control signals to apply to one or more of the variable capacitors to minimize impedance mismatching, thus improving operational efficiency. In at least some embodiments, such a data structure  410  is pre-programmed by an engineer or designer. 
         [0022]    At least one of the data structures  410  cross-references multiple possible operating conditions (e.g., position of electronic device containing antenna and components  400 ) with multiple possible control signals that may be applied to one or more variable capacitors on the antenna. Thus, upon receiving data regarding such operating conditions from one or more sensors  406 , the processor  401  may use such a data structure to determine the capacitance(s) on one or more of the variable capacitors that would minimize impedance mismatch, thus improving operational efficiency. In at least some embodiments, such a data structure  410  is pre-programmed by an engineer or designer. 
         [0023]    At least one of the algorithms  412  contains code, executable by processor  401 , that instructs the processor  401  regarding how to adjust the control signals applied to one or more of the variable capacitors in the event that the closed loop tuning module  308  ( FIG. 3 ) detects an impedance mismatch. Such code is application-specific and may be designed as suitable, but it should aim to minimize impedance mismatching detected by the closed loop tuning module  308 . The code may be programmed by an engineer or designer. 
         [0024]    In some embodiments, one or more of the actions performed by the processor  401  as described above may instead be performed by an optional, dedicated controller  408 . For instance and without limitation, the controller  408  may be responsible for communicating with one or more of the variable capacitors. In some embodiments, the controller  408  may itself be controlled by, or may operate in coordination with, the processor  401 . 
         [0025]      FIG. 5A  is a flow diagram of a method  500  in accordance with embodiments of the invention. The method  500  begins with the processor collecting data from the sensor(s), closed-loop tuning module, and/or the transceiver (step  502 ). As previously explained, such data may include, without limitation, information about operating conditions (e.g., position of electronic device or proximity to body parts) and/or an impedance mismatch indication. The method  500  next comprises using the received data to determine whether an impedance mismatch exists between the antenna and transceiver or if a mismatch is imminent (e.g., due to changing operating conditions) (step  504 ). In the case of data from the closed-loop tuning module (e.g., module  308  in  FIG. 3 ), the existence of an impedance mismatch is already evident. In the case of data from sensors, a data structure  410  ( FIG. 4 ) is used to determine whether impedance adjustments are necessary. The method  500  then comprises using a lookup table (e.g., a data structure  410 ) and/or an algorithm (e.g., an algorithm  412 ) to identify the control signal(s) that should be applied to the variable capacitor(s) (step  506 ). Finally, the method  500  includes applying the control signal(s) to one or more of the variable capacitors (step  508 ). Because impedance matches are continuously monitored, control of the method  500  then returns to step  502 . 
         [0026]      FIG. 5B  is a flow diagram of a method  550  in accordance with embodiments of the invention. Unlike the method  500 , which is tailored to detecting impedance mismatch, the method  550  is typically used to ensure impedance matching when one or more of the operating frequencies of the electronic device are to be adjusted. In this way, impedance mismatches are ameliorated and efficiency is sustained or improved despite changes in the device&#39;s operating frequencies. The method  550  begins by determining the multiple target operating frequencies at which the electronic device is to operate (step  552 ). Lookup tables (e.g., one or more data structures  410 ) are used to determine the control signal(s) that correspond to the target operating frequencies (step  554 ). The control signal(s) are then applied to the variable capacitors so that the electronic device operates most efficiently at the target operating frequencies. The steps of methods  500  and  550  may be adjusted as desired, including the addition, deletion and/or rearrangement of one or more steps. 
         [0027]    Numerous other variations and modifications will become apparent to those skilled in the art once the above disclosure is fully appreciated. It is intended that the following claims be interpreted to embrace all such variations, modifications and equivalents. In addition, the term “or” should be interpreted in an inclusive sense.