Abstract:
A method of adapting an antenna to a transceiver system having a receiver subsystem and a transmitter subsystem comprises using an automatic tuning system to tune the antenna with respect to the receiver subsystem. The tuning results in an optimal receive signal at the receiver subsystem in response to RF energy radiated to the antenna. The tuning system may include a tuning detection element for radiating RF energy to the antenna, and a tuning element for tuning the antenna. After tuning the antenna, the method further comprises tuning a tunable matching network, coupled between an output of an RF power device of the transmitter subsystem and an input of the antenna, to facilitate an optimal power transfer amount from the RF power device to the antenna while the RF power device operates according to certain desired parameters. The desired parameters may include output power and efficiency.

Description:
RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/346,033, filed on Jun. 6, 2016; U.S. Provisional Application No. 62/326,375, filed on Apr. 22, 2016; and is a continuation-in part of U.S. application Ser. No. 15/456,430, filed on Mar. 10, 2017. The entire teachings of the above applications are incorporated herein by reference. 
     
    
     GOVERNMENT SUPPORT 
       [0002]    This invention was made with government support under CON02458-1 awarded by the Defense Advanced Research Projects Agency (DARPA). The government has certain rights in the invention. 
     
    
     BACKGROUND 
       [0003]    An RF transmitter/receiver (transceiver) may be electrically coupled to an antenna to transmit and receive electromagnetic radiation. The electrical coupling can be designed to create a conjugate impedance match between the transceiver and the antenna, which maximizes the power transfer between the transceiver and the antenna. In a controlled environment, the antenna input impedance remains constant, so a fixed electrical coupling generally maintains the conjugate match. In real-world environments, however, antenna detuning may occur when the input impedance of the antenna is perturbed by various factors (e.g., objects near the antenna or agents such as ice forming directly on the antenna structure). 
         [0004]    Small RF transceivers, with correspondingly small antennas, are especially susceptible to performance degradation if the impedance of the antenna is perturbed. Antenna detuning reduces the power available to the receiver and the transmit power radiated, but it can also severely degrade the efficiency of the power amplifier in the transmitter portion of the transceiver. A conventional solution is to add a tunable impedance matching network before the antenna, along with a tuning detection network, both of which add significant losses. 
       SUMMARY OF THE INVENTION 
       [0005]    The described embodiments of a transceiver tuning system combine two tuning techniques. Both of these tuning techniques utilize signal detection methods that do not add loss in the RF path. 
         [0006]    A first tuning technique relates to a tunable antenna, with embedded tuning detection components, operative to ensure that the receiver functions efficiently and effectively. The first tuning technique utilizes sensors, test signal sources, and tuning components, embedded within the antenna itself, to adjust the antenna feedpoint impedance. 
         [0007]    A second tuning technique involves an adaptive impedance matching system, disposed between the output of the transceiver&#39;s power amplifier and the transmit/receive switch. The adaptive impedance matching network is operative to compensate for the remaining impedance mismatch between the transceiver&#39;s power amplifier and the antenna feedpoint to ensure efficient operation. 
         [0008]    The losses in a matching network are related to the ratio of the impedances being matched. In general, a higher the ratio results in a larger loss. In the described embodiments, the first tuning technique (adjusting the tunable antenna) operates to manipulate the antenna to exhibit a feedpoint impedance that is close enough to the receiver&#39;s input impedance to ensure good receiver performance. The resulting antenna impedance significantly reduces the impedance matching ratio that the second tuning technique (i.e., the tunable matching network) must accommodate. 
         [0009]    A lower impedance ratio reduces the loss in the transmit path, which maximizes transmitted power. Reducing losses also extends the life of the energy storage device (e.g., battery) powering the transceiver, since less energy is wasted through the losses. Another benefit of the lower ratio is a reduction in the complexity and physical space requirements (i.e., size) of the matching network components. 
         [0010]    The described embodiments utilize an E-field probe along with other tuning components, all embedded in the antenna, to perform the required tuning detection for both transmit and receive operations. This configuration eliminates the losses and bulk associated with components associated with conventional tuning detection devices. 
         [0011]    The losses that are incurred when matching two impedances increase non-linearly as the real-part impedance ratio increases. By using the tunable matching network directly on the output of the transmitter&#39;s power transistor, the fixed matching network is eliminated, thereby reducing size, loss and parts count. The described embodiments trade off variations in the reflection loss against the variations in matching insertion loss, to find a tuning solution that always maximizes the RF power delivered to the antenna, consistent with a desired DC power consumption. 
         [0012]    In one aspect, the invention may be a method of adapting an antenna to a transceiver system having a receiver subsystem and a transmitter subsystem. The method may comprise tuning the antenna with respect to the receiver subsystem using an automatic tuning system, to result in an optimal receive signal at the receiver subsystem in response to RF energy radiated to the antenna. After tuning the antenna with respect to the receiver subsystem, the method may further comprise tuning a tunable matching network, coupled between an output of an RF power device of the transmitter subsystem and an input of the antenna, to facilitate an optimal power transfer amount from the RF power device to the antenna while the RF power device operates according to one or more desired parameters. 
         [0013]    In an embodiment, tuning the antenna may further include radiating constant-amplitude RF energy at a desired frequency, proximate the antenna, from a tuning detection element that is coupled to a mode of the antenna, and located outside of a signal path of the antenna and separated from the antenna by a gap. The constant-amplitude RF energy may be radiated in accordance with at least one mode of the antenna to which the tuning detection element is coupled. Tuning the antenna may further include receiving a signal from the antenna in response to the radiated constant-amplitude RF energy, monitoring an amplitude of the received signal, and tuning a resonant frequency of the antenna to the desired frequency, with a tuning element, based on the monitored amplitude. 
         [0014]    Tuning the antenna may comprise maximizing the amplitude of the received signal. Tuning the antenna may comprise radiating additional RF energy in accordance with at least one additional mode of the antenna. The tuning detection element may have a resonant frequency that is non-overlapping with a frequency band of the antenna. 
         [0015]    In an embodiment, tuning the tunable matching network may further include generating, with a current sensor, a supply current value corresponding to an amount of supply current delivered to the RF power device, and generating, with an RF power sensing device, a power sensor value that is monotonically related to an amount of power delivered to the antenna. Tuning the tunable matching network may further include providing at least one tuning signal, generated as a function of the supply current value and the power sensor value, to at least one tunable component of the tunable matching network. 
         [0016]    Tuning the tunable matching network may further include adjusting the at least one tuning signal to a setting that results in the power sensor value being at least as large as for other settings of the at least one tuning signal, while maintaining the RF power device supply current value at a predetermined amount. Determining the predetermined amount may be accomplished by measuring an amount of supply current that occurs when the RF power device is driving a load that elicits a desired output power and efficiency from the RF power device. 
         [0017]    Tuning the tunable matching network may further include generating the at least one tuning signal by varying the at least one tuning signal according to a step-wise gradient evaluation of the current value and the power sensor value. Generating the power sensor value may be accomplished by measuring E-fields of the antenna with a capacitively-coupled probe. The capacitively-coupled probe may be a constitutive element of the antenna. 
         [0018]    In another aspect, the invention may be a system for adapting an antenna to a transceiver system having a receiver subsystem and a transmitter subsystem. The system may comprise an automatic antenna tuning system configured to tune the antenna with respect to the receiver subsystem, to result in an optimal receive signal at the receiver subsystem in response to RF energy radiated to the antenna. The system may further comprise an adaptive impedance matching system, comprising a tunable matching network coupled between an output of an RF power device of the transmitter subsystem and an input of the antenna. The adaptive impedance matching system may be configured to, after the antenna has been tuned with respect to the receiver subsystem, implement an impedance match between the output of the RF power device and the input of the antenna tunable matching network. Implementing the impedance match facilitates an optimal power transfer amount, from the RF power device to the antenna, that occurs while the RF power device operates according to one or more desired parameters. 
         [0019]    In an embodiment, the automatic antenna tuning system comprises a tuning detection element coupled to a mode of the antenna. The tuning detection element transmits constant-amplitude RF energy, at a desired frequency, to the antenna in accordance with at least one mode of the antenna to which the tuning detection element is coupled. The tuning detection element located outside of a signal path conveying a signal to the antenna and separated from the antenna by a gap. The automatic antenna tuning system further comprises a processor configured to monitor an amplitude of the signal received by the antenna in response to the radiated constant-amplitude RF energy, and a tuning element for tuning a resonant frequency of the antenna to the desired frequency based on an instruction from the processor. 
         [0020]    In an embodiment, the instruction from the processor may maximize the received signal. The automatic antenna tuning system may further comprise a feedback path for transmitting a portion of an output of the signal path to the processor. The automatic antenna tuning system may further comprise at least one additional tuning detection element for operation in accordance with at least one additional mode of the antenna. 
         [0021]    The adaptive impedance matching system may comprises a matching network having at least one tunable component, a current sensor configured to provide a supply current value corresponding to an amount of supply current delivered to the RF power device, an RF power sensor configured to provide a power sensor value that is monotonically related to an amount of power delivered to the antenna, and a tuner configured to provide a tuning signal to the matching network. The tuning signal may be a function of the supply current value and the RF power sensor value. The tuner may adjust the tuning signal to a setting that results in the power sensor value being at least as large as for other settings of the at least one tuning signal, while maintaining the RF power device supply current value at a predetermined amount. The predetermined amount may be an amount of RF power device supply current that occurs when the RF power device is driving a load that elicits a desired output power and efficiency from the RF power source. 
         [0022]    In an embodiment, an input impedance of the antenna is complex. The tuner may generate the at least one tuning signal using a step-wise gradient search. The antenna may be an electrically small antenna. The power sensor may be a capacitively-coupled probe configured to measure E-fields generated by the antenna. The capacitively-coupled probe may be a constitutive element of the antenna. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]    The foregoing will be apparent from the following more particular description of example embodiments of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating embodiments of the present invention. 
           [0024]      FIG. 1  illustrates a block diagram of a conventional transceiver system. 
           [0025]      FIG. 2  illustrates an example embodiment of a transceiver tuning system constructed and arranged according to the invention. 
           [0026]      FIG. 3  is a diagram of an example internal structure of a processing system that may be used to implement embodiments of the tuning controller. 
           [0027]      FIG. 4  illustrates one embodiment of a method of implementing a transceiver tuning system. 
           [0028]      FIG. 5  illustrates an example of tuning the antenna with an automatic tuning system. 
           [0029]      FIG. 6  illustrates an example of tuning a tunable matching network. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0030]    A description of example embodiments of the invention follows. 
         [0031]    The teachings of all patents, published applications and references cited herein are incorporated by reference in their entirety. 
         [0032]      FIG. 1  illustrates a block diagram of a conventional transceiver system  100 , with a tunable matching network  102 , configured to monitor and minimize reflected power. Elements of the tunable matching network  102  are electrically manipulated by a tuning controller  104  to present a specific impedance (e.g., 50Ω) to the transmitter  106  and the receiver  108  of the transceiver system  100 , while compensating for impedance variations at the antenna feedpoint due to antenna detuning effects. The tuning controller  104  generates the control signals  110  based on forward and reverse power, sensed by RF detectors  112 , of propagating RF energy coupled from the RF path by a dual directional coupler  114 . The tuning controller manipulates the elements of the matching network  102 , through the control signals, to minimize the ratio of the reflected RF power to the forward RF power. 
         [0033]    One disadvantage of the system  100  shown in  FIG. 1  is excessive loss from the impedance matching circuits. System  100  utilizes two matching networks. A first, fixed matching network  116  within the transmitter  106  to match the transmitter&#39;s power amplifier transistor to a transmission path impedance (e.g. 50Ω), and the tunable matching network  102 . The impedance transformation affected by the fixed matching network  116  necessarily introduces RF power loss. The RF power loss is proportional to the ratio of the real parts of the impedance transformation. High efficiency RF power amplifiers typically have a low output impedance (e.g., within a range of 10Ω to 20Ω), so amplifier output matching network  116  may exhibit significant RF power loss. The tunable matching network  102  compensates for the entire mismatch presented by the antenna, so the tunable matching network loss can also be quite high. Although the loss in the transmit path wastes power, the same loss in the receive path will increase the noise figure of the receiver by attenuating incoming signals. 
         [0034]    Another disadvantage of the system  100  shown in  FIG. 1  is loss introduced by the dual directional coupler  114 , which typically is 0.5 dB or more. Yet another disadvantage of the system  100  shown in  FIG. 1  is the size, cost and complexity of the required components. As described herein, two separate matching networks are required (the fixed matching network  116  and the tunable matching network  102 ). Further, the dual directional coupler  114 , designed to operate at typical cellular frequencies, may occupy significant physical space. While miniaturized couplers exist, such smaller couplers tend to exhibit higher losses than their larger counterparts. 
         [0035]    To attain a desired transmit power at the antenna feedpoint, the transmitter must produce RF power higher than the desired feedpoint power level in order to compensate for the losses incurred by the fixed matching network  116  and the tunable matching network  102 . The T/R switch  118  needs to be robust enough to handle this higher power, which may require increased cost, size and complexity. 
         [0036]    Finally, tuning for minimum reflected power may not guarantee maximum power to the antenna feedpoint. Because the loss through the tunable matching network  102  is not fixed, tuning for minimum reflected power does not account for the possibility that the loss through the tunable matching network  102  may be significantly higher than at a slightly different tuning point. 
         [0037]      FIG. 2  illustrates an example embodiment of a transceiver tuning system  200  constructed and arranged according to the invention. The transceiver tuning system  200  is shown with a tunable antenna system  201  comprising, for simplicity, a single polarization tunable patch antenna  202 . It should be understood, however, that in alternative embodiments the described tuning techniques may be used to tune a transceiver system that comprises alternative antenna configurations. 
         [0038]    The tunable antenna  201  further comprises an embedded E-field probe  204  that can either inject a tuning signal from a pilot tone generator  206 , or couple energy from the transmit signal to an RF detector  208 , depending on the state of the tune/detect switch  210 . The output of the RF detector  208  is provided to the tuning controller  226 . The tunable antenna  201  also comprises an electronically controlled tuning capacitor  211  to adjust the electrical characteristics (e.g., resonant frequency) of the patch antenna  202 , although other embodiments may include alternative techniques and components for adjusting the electrical characteristics of the antenna. 
         [0039]    Although the example embodiments described herein utilize a single E-field probe  204 , the disclosed concepts may be extended to more than one such probe. For example, U.S. Pat. No. 8,472,094, the entire contents of which are incorporated by reference herein, describes a dual-mode antenna with two E-field probes and a quadrature network for the pilot tone. The described embodiments may utilize the E-field probes and quadrature network of such an antenna configuration, consistent with the concepts disclosed herein, to correct for polarization errors, thereby achieving high quality circular polarization. Other antenna configurations may similarly be used in conjunction with the described embodiments of a transceiver tuning system. 
         [0040]    The RF power source  212  includes an RF power transistor  214 , an RF drive source  216 , and a gate match and bias network  218 . The RF drive source  216  provides an RF signal, through the gate match and bias network  218  to the gate of the RF power transistor  214 . The RF signal causes the RF power transistor  214  to control the flow of supply current  220  from the drain supply to ground. The output of the RF power source  212  is taken from the drain of the RF power transistor  214 . The RF power source  212  further includes a supply current monitor  222  that provides a current sense signal  224  to a tuning controller  226  that corresponds to the supply current  220  supplied to the RF power transistor  208 . In this example embodiment, the current monitor  222  employs a resistor and a differential amplifier, which produces the current sense signal  224  that is an amplified version of the voltage drop across the resistor. It should be understood, however, that other techniques known in the art for sensing an amount of current flow may alternatively be used. Although a Field Effect Transistor (FET) is shown for the RF power device in the example embodiment, the RF power device could be implemented with other components, e.g., other types of transistors, or a vacuum tube. 
         [0041]    A transmit/receive (T/R) switch  228  selectively connects a feedpoint  230  of the patch antenna  202  to either the matching network  204  or a low noise amplifier (LNA)  232 . The LNA  232  drives a tune/receive switch  234 , which selectively directs the output of the LNA  232  to either a receiver system  236  or an RF detector  238 . The output of the RF detector  238  is provided to the tuning controller  226 . In the example embodiment, the RF detector  238  is a log power detector, although other embodiments may use alternative detector types. 
         [0042]    The tunable antenna  201  of the example embodiment is controlled by a tuning controller  240  through a digital to analog converter (DAC)  242 . The tuning controller  240  provides certain control functionality within the tunable antenna, such as the control of the tune/detect switch  210 , the T/R switch  228  and the tune/receive switch  234 , although the connections from the controller  240  to these components are not explicitly shown. 
         [0043]    The DAC  242  drives an antenna control signal  243  to the electronically controlled tuning capacitor  211  to adjust electrical characteristics of the patch antenna  202 . The tunable matching network  204  is controlled by the tuning controller  240  through dual DAC  244 . The dual DAC  244  drives matching network control signals  245  to the variable components in the tunable matching network  204  (variable capacitors in this example embodiment). In both cases, the tuning controller  240  generates the control signals based on one or more of the drain current sense signal  224 , the output of the RF detector  208  and the output RF detector  238 . 
         [0044]    The transceiver tuning system  200  is initially tuned for receive operation by the microcontroller  240  setting the T/R switch  228  to drive the LNA  232  (switch control signals not shown), and setting the tune/detect switch  210  to connect the pilot tone generator  206  to couple pilot tone energy into the patch antenna  202  through the embedded E-field probe  204 . The tuning controller  240  adjusts the antenna tuning capacitor  211  through the DAC  242  to maximize the LNA output  232 , which is detected by the RF detector  238  through the tune/receive switch  234 . Adjusting the antenna tuning capacitor  211  effectively modifies the resonant frequency of the antenna. Once the signal produced by the RF detector has been maximized, the antenna center frequency will match that of the pilot tone generator, and the impedance match of the antenna will be close to 50 Ohms. 
         [0045]    Subsequent to performing the receive operation tuning, the controller  240  performs tuning for transmit operation with an adaptive impedance matching system. For transmit operation tuning, the tuning controller  240  sets the T/R switch  228  is set to transmit (i.e., the T/R switch connects the matching network  204  to the antenna feedpoint  230 ), and the tuning controller  240  sets the tune/detect switch  210  is set to connect the E-field probe  204  to the RF detector  208 . 
         [0046]    Before the system is deployed, and in the absence any perturbation of the antenna impedance, a baseline value of the drain current  220  is measured when the RF power device  214  is operating both at maximum efficiency and the desired output power. In normal operation, the tunable impedance matching network  204  is adjusted to simultaneously maximize the RF voltage detected by the RF detector through the antenna probe  204 , while maintaining the same baseline value of supply current  220  for the RF power device  214  that was established prior to deployment. This tuning state guarantees efficient operation of the RF power device  214  (or at least operation at an acceptable DC input power level), consistent with the maximum RF signal at the antenna. An example of this operation of the tunable matching system is presented in U.S. patent application Ser. No. 15/456,430, filed Mar. 10, 2017 and entitled “Low-Loss Compact Transmit Impedance Match Tuning Technique,” the entire contents of which are incorporated by reference herein. 
         [0047]    Although the matching network  204  is shown as a “PI” configuration on the output of the transistor  214 , it should be understood that the transceiver tuning system described herein will work with any type of tunable impedance matching circuit or device. 
         [0048]      FIG. 3  is a diagram of an example internal structure of a processing system  300  that may be used to implement one or more of the embodiments of the tuning controller  240  described herein. Other processing structures may alternatively be used. 
         [0049]    The processing system  300  may contain a system bus  302 , where a bus may be a set of hardware lines used for data transfer among the components of a computer or processing system. The system bus  302  is essentially a shared conduit that connects different components of a processing system (e.g., processor, disk storage, memory, input/output ports, network ports, etc.) that enables the transfer of information between the components. 
         [0050]    Attached to the system bus  302  may be a user I/O device interface  304  for connecting various input and output devices (e.g., keyboard, mouse, displays, printers, speakers, etc.) to the processing system  300 . A network interface  306  allows the computer to connect to various other devices attached to a network  308 . Memory  310  provides volatile and non-volatile storage for information such as computer software instructions used to implement one or more of the embodiments of the present invention described herein. Memory  310  also provides volatile and non-volatile storage for data generated internally and for data received from sources external to the processing system  300 . 
         [0051]    A central processor unit  312  is also attached to the system bus  302  and provides for the execution of computer instructions stored in memory  310 . The system may also include support electronics/logic  314 , and a communications interface  316 . The communications interface may receive the RF power device supply current sense signal  224  from the current sensor  222 , and the RF sense signals from RF detector  208  and RF detector  238 . The communications interface  316  may provide the control signals  245  to the matching network  204 . 
         [0052]    In one embodiment, the information stored in memory  310  may comprise a computer program product, such that the memory  310  may comprise a non-transitory computer-readable medium (e.g., a removable storage medium such as one or more DVD-ROM&#39;s, CD-ROM&#39;s, diskettes, tapes, etc.) that provides at least a portion of the software instructions for the invention system. The computer program product can be installed by any suitable software installation procedure, as is well known in the art. In another embodiment, at least a portion of the software instructions may also be downloaded over a cable communication and/or wireless connection. 
         [0053]      FIG. 4  illustrates one embodiment of a method  400  of implementing a transceiver tuning system. The method  400  includes tuning  402  the antenna with an automatic tuning system, such that a first power transfer amount from the RF power source to the antenna is less than a maximum power transfer amount. The method  400  further includes tuning a tunable matching network, coupled between an output of the RF power source and an input of the antenna, such that a second power transfer amount from the RF power source to the antenna is greater than the first power transfer value. 
         [0054]      FIG. 5  illustrates an example of tuning  402  the antenna with an automatic tuning system, including radiating  502  energy proximate the antenna from a tuning detection element that is (i) coupled to a mode of the antenna, and (ii) located outside of a signal path of the antenna and separated from the antenna by a gap, the energy being radiated in accordance with at least one mode of the antenna to which the tuning detection element is coupled. Tuning  402  the antenna further includes receiving  504  a signal from the antenna in response to the energy radiated in accordance with the at least one mode, monitoring  506  an amplitude of the received signal, and tuning  508  a resonant frequency of the antenna to the desired frequency with a tuning element, based on the monitored amplitude. 
         [0055]      FIG. 6  illustrates an example of tuning  404  a tunable matching network, including generating  602 , with a current sensor, a supply current value corresponding to an amount of supply current delivered to the RF power device. The tuning  404  further includes generating  604 , with an RF power device, a power sensor value that is monotonically related to an amount of power delivered to the antenna. The tuning  404  also includes providing  606  at least one tuning signal, generated as a function of the supply current value and the power sensor value, to a matching network having at least one tunable component 
         [0056]    It will be apparent that one or more embodiments described herein may be implemented in many different forms of software and hardware. Software code and/or specialized hardware used to implement embodiments described herein is not limiting of the embodiments of the invention described herein. Thus, the operation and behavior of embodiments are described without reference to specific software code and/or specialized hardware—it being understood that one would be able to design software and/or hardware to implement the embodiments based on the description herein. 
         [0057]    Further, certain embodiments of the example embodiments described herein may be implemented as logic that performs one or more functions. This logic may be hardware-based, software-based, or a combination of hardware-based and software-based. Some or all of the logic may be stored on one or more tangible, non-transitory, computer-readable storage media and may include computer-executable instructions that may be executed by a controller or processor. The computer-executable instructions may include instructions that implement one or more embodiments of the invention. The tangible, non-transitory, computer-readable storage media may be volatile or non-volatile and may include, for example, flash memories, dynamic memories, removable disks, and non-removable disks. 
         [0058]    While this invention has been particularly shown and described with references to example embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.