Patent Publication Number: US-10778043-B2

Title: High frequency wireless power transmission system

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application No. 62/679,464 filed Jun. 1, 2018, which is incorporated by reference as if fully set forth. 
    
    
     FIELD OF INVENTION 
     The embodiments described herein provide high frequency wireless power transmission system (WPTS) architectures suitable for delivering focused, directional wireless power to one or more wireless power receiver clients (WPRCs). 
     BACKGROUND 
     A typical WPTS may comprise thousands of antennas to transmit accurate, focused, directional power to one or more WPRCs. In a point-to-point architecture, as the number of antennas increases, the number of connections between the individual antennas and a central controller increases. Such a point-to-point architecture may be expensive to manufacture due to the increased connections. Intermediate collector chips may be added to the point-to-point architecture, but adding these intermediate collector chips would also increase manufacturing costs. As such, there is a need for an architecture that scales well to accommodate an increased number of antennas without significantly driving up manufacturing costs. 
     SUMMARY 
     Described herein are embodiments of a WPTS and a WPRC and methods of operation thereof. In some embodiments, a WPTS may include an antenna array controller, a plurality of antenna controllers, and a daisy chain bus coupling the antenna array controller and the plurality of antenna controllers. In some embodiments, each antenna controller of the plurality of antenna controllers may be coupled to a respective plurality of antennas. In some embodiments, the antenna array controller may be configured to control the antenna controllers to receive a phase beacon from the WPRC and to transmit wireless power to the WPRC based on information encoded in the phase beacon. 
     In some embodiments, the daisy chain bus may be a differential pair. 
     In some embodiments, each antenna controller of the plurality of antenna controllers may include a plurality of antenna management units (AMUs). In some embodiments, each AMU may include one of the respective plurality of antennas and a single phase locked loop (PLL) may be shared across the one or more AMUs. 
     In some embodiments, the AMU may be configured to, when operating in a receive mode, detect phase information from the received phase beacon. In some embodiments, the AMU may be configured to, when operating in a transmit mode, program a phase of a phase shifter based on a complex conjugate of the phase information and transmit wireless power to the WPRC via the phase shifter. 
     In some embodiments, each antenna controller of the plurality of antenna controllers may be configured to update a payload list indicating the information encoded in the phase beacon and forward the updated payload list on the daisy chain bus. 
     In some embodiments, the updated payload list may include a count indicating how many antennas received the information encoded in the phase beacon. In some embodiments, the information encoded in the phase beacon may include a WPRC ID. In some embodiments, the updated payload list may include a list of one or more received WPRC IDs. 
     In some embodiments, each antenna controller of the plurality of antenna controllers may be configured to receive a timing beacon prior to the phase beacon. In some embodiments, the timing beacon may be received on a frequency that is offset from a frequency used to transmit the wireless power. 
     In some embodiments, the antenna array controller may be further configured to control the plurality of antenna controllers to halt transmission of wireless power during a time slot corresponding to an expected receive time of the phase beacon. 
     In some embodiments, the antenna array controller may be further configured to send a command message to the plurality of antenna controllers using a command bus synchronized with a reference clock. In some embodiments, the command message may be synchronized with a divided-down version of the reference clock. In some embodiments, the command message may be synchronized with an integer divided-down version of the reference clock. 
     In some embodiments, each antenna controller of the plurality of antenna controllers may include a phase locked loop. In some embodiments, the command message may be used to synchronized phase locked loops across the plurality of antenna controllers. 
     In some embodiments, the antenna array controller may be configured to determine a number of the plurality of antenna controllers coupled to the daisy chain bus based on a message that propagates through the plurality of antenna controllers and is returned to the antenna array controller. In some embodiments, a value included in the message may be incremented by each antenna controller of the plurality of antenna controllers. In some embodiments, the antenna array controller may be further configured to determine the number of the plurality of antenna controllers based on the value that is returned to the antenna array controller. 
     In some embodiments, the wireless power may be transmitted in an industrial, scientific, and medical (ISM) band at 2.4 GHz, 5.8 GHz, 24 GHz, or 60 GHz. 
     In some embodiments, a WPTS may receive one or more phase beacon payloads at an antenna controller via a first set of antennas. In some embodiments, on a condition that a phase beacon payload of the one or more phase beacon payloads matches a payload in a payload list, the WPTS may increment a count corresponding to the payload in the payload list. In some embodiments, on a condition that the phase beacon payload does not match a payload in the payload list, the WPTS may add an indication of the phase beacon payload to the payload list. In some embodiments, the WPTS may forward the payload list on a daisy chain bus to a next antenna controller or to an antenna array controller and transmit wireless power based on the payload list. 
     In some embodiments, on the condition that the phase beacon payload matches the payload in the payload list, the WPTS may increment the count corresponding to the payload in the payload list based on how many antennas of the first set of antennas received the phase beacon payload. 
     In some embodiments, the phase beacon payload may include a WPRC ID. In some embodiments, the phase beacon payload may include an indication of a state of charge of a WPRC. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts a system diagram including an example wireless power transmission environment. 
         FIG. 2  is a block diagram illustrating example components of an example embodiment of a WPTS. 
         FIG. 3  is a block diagram illustrating an example embodiment of a WPRC. 
         FIG. 4  is a diagram illustrating an example embodiment of a wireless signal delivery environment. 
         FIG. 5  is a diagram of an example embodiment of a wireless power delivery system based on a point-to-point architecture. 
         FIG. 6  is a diagram of another example embodiment of a wireless power delivery system based on a daisy chain architecture. 
         FIG. 7  is a diagram depicting a system including a plurality of antenna controllers, an antenna array controller, and a clock generator. 
         FIG. 8  is a diagram of an antenna management unit. 
         FIG. 9  is a timing diagram depicting timing beacons, phase beacons, and wireless power transmissions. 
         FIG. 10  is a diagram depicting the propagation of a payload list around a daisy-chained arrangement of antenna controllers and an antenna array controller. 
         FIG. 11  is a flow diagram depicting an example method that may be performed by a WPTS or an antenna controller of a WPTS. 
         FIG. 12  depicts field pocket sizes corresponding to different wireless power transmission frequencies. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  depicts a system diagram including an example wireless power transmission environment  100  illustrating wireless power delivery from one or more WPTSs, such as WPTS  101 . More specifically,  FIG. 1  illustrates power transmission to one or more WPRCs  110   a - 110   c . WPTS  101  may be configured to receive encoded beacons  111   a - 111   c  from WPRCs  110   a - 110   c  and transmit wireless power  112   a - 112   c  to WPRCs  110   a - 110   c . Wireless data  113   a - 113   c  may also be bidirectionally exchanged between WPTS  101  and WPRCs  110   a - 110   c . WPRCs  110   a - 110   c  may be configured to receive and process wireless power  112   a - 112   c  and wireless data  113   a - 113   c  from one or more WPTSs, such as WPTS  101 . Components of an example WPTS  101  are shown and discussed in greater detail below, as well as in  FIG. 2 . Components of an example WPRC  110   a - 110   c  are shown and discussed in greater detail with reference to  FIG. 3 . 
     WPTS  101  may include multiple antennas  103   a - 103   n , e.g., an antenna array including a plurality of antennas, which may be capable of delivering wireless power  112   a - 112   c  to WPRCs  110   a - 110   c . Antennas  103   a - 103   n  may further include one or more timing acquisition antennas and one or more communication antennas. In some embodiments, the same antennas for transmission of wireless power may be used for timing acquisition and wireless data communication. In alternative embodiments, separate antennas may be used for wireless power, for timing acquisition, and for wireless data communication. In some embodiments, the antennas are adaptively-phased radio frequency (RF) antennas. The WPTS  101  may be capable of determining the appropriate phases with which to deliver a coherent power transmission signal to WPRCs  110   a - 110   c . Each antenna of the antenna array including antennas  103   a - 103   n  may be configured to emit a signal, e.g. a continuous wave or pulsed power transmission signal, at a specific phase relative to each other antenna, such that a coherent sum of the signals transmitted from a collection of the antennas is focused at a location of a respective WPRC  110   a - 110   c . Any number of antennas may be employed in the reception and transmission of signals depicted in  FIG. 1 . Multiple antennas, including a portion of antennas  103   a - 103   n  that may include all of antennas  103   a - 103   n , may be employed in the transmission and/or reception of wireless signals. It is appreciated that use of the term “array” does not necessarily limit the antenna array to any specific array structure. That is, the antenna array does not need to be structured in a specific “array” form or geometry. Furthermore, as used herein the term “array” or “array system” may be used include related and peripheral circuitry for signal generation, reception and transmission, such as radios, digital circuits and modems. 
     As illustrated in the example of  FIG. 1 , antennas  103   a - 103   n  may be included in WPTS  101  and may be configured to transmit both power and data and to receive data. The antennas  103   a - 103   n  may be configured to provide delivery of wireless radio frequency power in a wireless power transmission environment  100 , to provide data transmission, and to receive wireless data transmitted by WPRCs  110   a - 110   c , including encoded beacon signals  111   a - 111   c . In some embodiments, the data transmission may be through lower power signaling than the wireless radio frequency power transmission. In some embodiments, one or more of the antennas  103   a - 103   n  may be alternatively configured for data communications in lieu of wireless power delivery. In some embodiments, one or more of the power delivery antennas  103   a - 103   n  can alternatively or additionally be configured for data communications in addition to or in lieu of wireless power delivery. The one or more data communication antennas are configured to send data communications to and receive data communications from WPRCs  110   a - 110   c.    
     Each of WPRCs  110   a - 110   c  may include one or more antennas (not shown) for transmitting signals to and receiving signals from WPTS  101 . Likewise, WPTS  101  may include an antenna array having one or more antennas and/or sets of antennas, each antenna or set of antennas being capable of emitting continuous wave or discrete (pulse) signals at specific phases relative to each other antenna or set of antennas. As discussed above, WPTSs  101  is capable of determining the appropriate phases for delivering the coherent signals to the antennas  103   a - 103   n . For example, in some embodiments, delivering coherent signals to a particular WPRC can be determined by computing the complex conjugate of a received encoded beacon signal at each antenna of the array or each antenna of a portion of the array such that a signal from each antenna is phased appropriately relative to a signal from other antennas employed in delivering power or data to the particular WPRC that transmitted the beacon signal. The WPTS  101  can be configured to emit a signal (e.g., continuous wave or pulsed transmission signal) from multiple antennas using multiple waveguides at a specific phase relative to each other. Other techniques for delivering a coherent wireless power signal are also applicable such as, for example, the techniques discussed in U.S. patent application Ser. No. 15/852,216 titled “Anytime Beaconing In A WPTS” filed Dec. 22, 2017 and in U.S. patent application Ser. No. 15/852,348 titled “Transmission Path Identification based on Propagation Channel Diversity” filed Dec. 22, 2017; which are expressly incorporated by reference herein. 
     Although not illustrated, each component of the wireless power transmission environment  100 , e.g., WPRCs  110   a - 110   c , WPTS  101 , can include control and synchronization mechanisms, e.g., a data communication synchronization module. WPTS  101  can be connected to a power source such as, for example, a power outlet or source connecting the WPTSs to a standard or primary alternating current (AC) power supply in a building. Alternatively, or additionally, WPTS  101  can be powered by a battery or via other mechanisms, e.g., solar cells, etc. 
     As shown in the example of  FIG. 1 , WPRCs  110   a - 110   c  include mobile phone devices and a wireless tablet. However, WPRCs  110   a - 110   c  can be any device or system that needs power and is capable of receiving wireless power via one or more integrated WPRCs. Although three WPRCs  110   a - 110   c  are depicted, any number of WPRCs may be supported. As discussed herein, a WPRC may include one or more integrated power receivers configured to receive and process power from one or more WPTSs and provide the power to the WPRCs  110   a - 110   c  or to internal batteries of the WPRCs  110   a - 110   c  for operation thereof. 
     As described herein, each of the WPRCs  110   a - 110   c  can be any system and/or device, and/or any combination of devices/systems that can establish a connection with another device, a server and/or other systems within the example wireless power transmission environment  100 . In some embodiments, the WPRCs  110   a - 110   c  may each include displays or other output functionalities to present or transmit data to a user and/or input functionalities to receive data from the user. By way of example, WPRC  110   a  can be, but is not limited to, a video game controller, a server desktop, a desktop computer, a computer cluster, a mobile computing device such as a notebook, a laptop computer, a handheld computer, a mobile phone, a smart phone, a PDA, a Blackberry device, a Treo, and/or an iPhone, etc. By way of example and not limitation, WPRC  110   a  can also be any wearable device such as watches, necklaces, rings or even devices embedded on or within the customer. Other examples of WPRC  110   a  include, but are not limited to, a safety sensor, e.g. a fire or carbon monoxide sensor, an electric toothbrush, an electronic door lock/handle, an electric light switch controller, an electric shaver, an electronic shelf label (ESL), etc. 
     Although not illustrated in the example of  FIG. 1 , the WPTS  101  and the WPRCs  110   a - 110   c  can each include a data communication module for communication via a data channel. Alternatively, or additionally, the WPRCs  110   a - 110   c  can direct antennas to communicate with WPTS  101  via existing data communications modules. In some embodiments, the WPTS  101  can have an embedded Wi-Fi hub for data communications via one or more antennas or transceivers. In some embodiments, the antennas  103   a - 103   n  can communicate via Bluetooth™, Wi-Fi™, ZigBee™, etc. The WPRCs  110   a - 110   c  may also include an embedded Bluetooth™, Wi-Fi™, ZigBee™, etc. transceiver for communicating with the WPTS  101 . Other data communication protocols are also possible. In some embodiments the beacon signal, which is primarily referred to herein as a continuous waveform, can alternatively or additionally take the form of a modulated signal and/or a discrete/pulsed signal. 
     WPTS  101  may also include control circuit  102 . Control circuit  102  may be configured to provide control and intelligence to the WPTS  101  components. Control circuit  102  may comprise one or more processors, memory units, etc., and may direct and control the various data and power communications. Control circuit  102  may direct data communications on a data carrier frequency that may be the same or different than the frequency via which wireless power is delivered. Likewise, control circuit  102  can direct wireless transmission system  100  to communicate with WPRCs  110   a - 110   c  as discussed herein. The data communications can be, by way of example and not limitation, Bluetooth™, Wi-Fi™, ZigBee™, etc. Other communication protocols are possible. 
     It is appreciated that the use of the term “WPTS” does not necessarily limit the WPTS to any specific structure. That is, the WPTS does not need to be structured in a specific form or geometry. Furthermore, as used herein the term “transmission system” or “WPTS” may be used to include related and peripheral circuitry for signal generation, reception and transmission, such as radios, digital circuits and modems. 
       FIG. 2  is a block diagram illustrating example components of a WPTS  200  in accordance with the embodiments described herein. As illustrated in the example of  FIG. 2 , the WPTS  200  may include a control circuit  201 , external power interface  202 , and power system  203 . Control circuit  201  may include processor  204 , for example a base band processor, and memory  205 . Additionally, although only one antenna array board  208  and one transmitter  206  are depicted in  FIG. 2 , WPTS  200  may include one or more transmitters  206  coupled to one or more antenna array boards  208  and transmit signals to the one or more antenna array boards  208 . Although only one receiver is depicted in  FIG. 2 , one or more receivers  207  may be coupled to the one or more antenna array boards  208  and may receive signals from the one or more antennas  250   a - 250   n  of the one or more antenna array boards  208 . Each antenna array board  208  includes switches  220   a - 220   n , phase shifters  230   a - 230   n , power amplifiers  240   a - 240   n , and antenna arrays  250   a - 250   n . Although each switch, phase shifter, power amplifier, and antenna is depicted in a one-to-one relationship, this should not be construed as limiting. Additionally or alternatively, any number of switches, phase shifters, power amplifiers, and antennas may be coupled. Some or all of the components of the WPTS  200  can be omitted, combined, or sub-divided in some embodiments. Furthermore, the setting of the switches  220   a - 220   n  and phase shifters  230   a - 230   n  should not be construed as limiting. Any of the switches  220   a - 220   n , phase shifters  230   a - 230   n , and/or power amplifiers  240   a - 240   n , or any combination thereof, may be individually controlled or controlled in groups. The signals transmitted and received by the one or more antenna array boards  208  may be wireless power signals, wireless data signals, or both. 
     Control circuit  201  is configured to provide control and intelligence to the array components including the switches  220   a - 220   n , phase shifters  230   a - 230   n , power amplifiers  240   a - 240   n , and antenna arrays  250   a - 250   n . Control circuit  201  may direct and control the various data and power communications. Transmitter  206  can generate a signal comprising power or data communications on a carrier frequency. The signal can be comply with a standardized format such as Bluetooth™, Wi-Fi™, ZigBee™, etc., including combinations or variations thereof. Additionally or alternatively, the signal can be a proprietary format that does not use Bluetooth™, Wi-Fi™, ZigBee™, and the like, and utilizes the same switches  220   a - 220   n , phase shifters  230   a - 230   n , power amplifiers  240   a - 240   n , and antenna arrays  250   a - 250   n  to transmit wireless data as are used to transmit wireless power. Such a configuration may save on hardware complexity and conserve power by operating independently of the constraints imposed by compliance with the aforementioned standardized formats. In some embodiments, control circuit  201  can also determine a transmission configuration comprising a directional transmission through the control of the switches  220   a - 220   n , phase shifters  230   a - 230   n , and amplifiers  240   a - 240   n  based on an encoded beacon signal received from a WPRC  210 . 
     The external power interface  202  is configured to receive external power and provide the power to various components. In some embodiments, the external power interface  202  may be configured to receive, for example, a standard external 24 Volt power supply. In other embodiments, the external power interface  202  can be, for example, 120/240 Volt AC mains to an embedded DC power supply which may source, for example, 12/24/48 Volt DC to provide the power to various components. Alternatively, the external power interface could be a DC supply which may source, for example, 12/24/48 Volts DC. Alternative configurations including other voltages are also possible. 
     Switches  220   a - 220   n  may be activated to transmit power and/or data and receive encoded beacon signals based on the state of the switches  220   a - 220   n . In one example, switches  220   a - 220   n  may be activated, e.g. closed, or deactivated, e.g. open, for power transmission, data transmission, and/or encoded beacon reception. Additional components are also possible. For example, in some embodiments phase-shifters  230   a - 230   n  may be included to change the phase of a signal when transmitting power or data to a WPRC  210 . Phase shifter  230   a - 230   n  may transmit a power or data signal to WPRC  210  based on a phase of a complex conjugate of the encoded beaconing signal from WPRC  210 . The phase-shift may also be determined by processing the encoded beaconing signal received from WPRC  210  and identifying WPRC  210 . WPTS  200  may then determine a phase-shift associated with WPRC  210  to transmit the power signal. In an example embodiment, data transmitted from the WPTS  200  may be in the form of communication beacons which may be used to synchronize clocks with WPRC  210 . This synchronization may improve the reliability of beacon phase detection. 
     In operation, control circuit  201 , which may control the WPTS  200 , may receive power from a power source over external power interface  202  and may be activated. Control circuit  201  may identify an available WPRC  210  within range of the WPTS  200  by receiving an encoded beacon signal initiated by the WPRC  210  via at least a portion of antennas  250   a - 250   n . When the WPRC  210  is identified based on the encoded beacon signal, a set of antenna elements on the WPTS may power on, enumerate, and calibrate for wireless power and/or data transmission. At this point, control circuit  201  may also be able to simultaneously receive additional encoded beacon signals from other WPRCs via at least a portion of antennas  250   a - 250   n.    
     Once the transmission configuration has been generated and instructions have been received from control circuit  201 , transmitter  206  may generate and transfer one or more power and/or data signal waves to one or more antenna boards  208 . Based on the instruction and generated signals, at least a portion of power switches  220   a - 220   n  may be opened or closed and at least a portion of phase shifters  230   a - 230   n  may be set to the appropriate phase associated with the transmission configuration. The power and/or data signal may then be amplified by at least a portion of power amplifiers  240   a - 240   n  and transmitted at an angle directed toward a location of WPRC  210 . As discussed herein, at least a portion of antennas  250   a - 250   n  may be simultaneously receiving encoded beacon signals from additional WPRCs  210 . 
     As described above, a WPTS  200  may include one or more antenna array boards  208 . In one embodiment, each antenna array board  208  may be configured to communicate with a single WPRC  210 , so that a different antenna array board  208  of a plurality of antenna array boards  208  communicates with a different WPRC  210  of a plurality of WPRCs  210 . Such an implementation may remove a reliance on a communication method, such as a low-rate personal area network (LR-WPAN), IEEE 802.15.4, or Bluetooth Low Energy (BLE) connection to synchronize with a WPRC  210 . A WPTS  200  may receive a same message from a WPRC  210  via different antennas of antennas  250   a - 250   n . The WPTS  200  may use the replication of the same message across the different antennas to establish a more reliable communication link. In such a scenario, a beacon power may be lowered since the lower power can be compensated by the improved reliability owed to the replicated received signals. In some embodiments, it may also be possible to dedicate certain antennas or groups of antennas for data communication and dedicate other antennas or groups of antennas for power delivery. For example, an example WPTS  200  may dedicate  8  or  16  antennas of antennas  250   a - 250   n  to data communication at a lower power level than some number of remaining antennas that may be dedicated to power delivery at a relatively higher power level than the data communication. 
       FIG. 3  is a block diagram illustrating an example WPRC  300  in accordance with embodiments described herein. As shown in the example of  FIG. 3 , WPRC  300  may include control circuit  301 , energy storage  302 , a control module  303 , for example an Internet of Things (IoT) control module, transceiver  306  and associated one or more antennas  320 , power meter  309 , rectifier  310 , a combiner  311 , beacon signal generator  307 , beacon coding unit  308  and associated one or more antennas  321 , and switch  312  connecting the combiner  311  or the beacon signal generator  307  to one or more associated antennas  322   a - 322   n . The energy storage  302  may be, for example, a batter, a capacitor, or any other suitable energy storage device. Although not depicted, the WPRC  300  may include an energy harvesting circuit which may enable the WPRC  300  to operate with a capacitor for short term energy storage instead of or in addition to using a battery. Some or all of the depicted components in  FIG. 3  can be omitted, combined, or sub-divided in some embodiments. Some or all of the components depicted in  FIG. 3  may be incorporated in a single integrated chip (IC). It should be noted that although the WPTS  200  may use full-duplexing, WPRC  300  may additionally or alternatively use half-duplexing. A received and/or transmitted data rate may be, for example, 20 Mbps. However, higher or lower data rates may be implemented to achieve other design goals. The WPRC  300  may transmit acknowledgement (ACK) messages back to a WPTS, such as a WPTS  200  depicted in  FIG. 2 . Although not depicted, a local CPU may be incorporated into WPRC  300 . For example, the local CPU may be included in the control circuit  301 . 
     A combiner  311  may receive and combine the received power and/or data transmission signals received via one or more antennas  322   a - 322   n . The combiner can be any combiner or divider circuit that is configured to achieve isolation between output ports while maintaining a matched condition. For example, the combiner  311  can be a Wilkinson Power Divider circuit. The combiner  311  may be used to combine two or more RF signals while maintaining a characteristic impedance, for example, 50 ohms. The combiner  311  may be a resistive-type combiner, which uses resistors, or a hybrid-type combiner, which uses transformers. The rectifier  310  may receive the combined power transmission signal from the combiner  311 , if present, which may be fed through the power meter  309  to the energy storage  302  for charging. In other embodiments, each antenna&#39;s power path can have its own rectifier  310  and the DC power out of the rectifiers is combined prior to feeding the power meter  309 . The power meter  309  may measure the received power signal strength and may provide the control circuit  301  with this measurement. 
     Energy storage  302  may include protection circuitry and/or monitoring functions. Additionally, the energy storage  302  may include one or more features, including, but not limited to, current limiting, temperature protection, over/under voltage alerts and protection, and capacity monitoring, for example coulomb monitoring. The control circuit  301  may receive the energy level from the energy storage  302  itself. The control circuit  301  may also transmit/receive via the transceiver  306  a data signal on a data carrier frequency, such as the base signal clock for clock synchronization. The beacon signal generator  307  may generate the beacon signal or calibration signal and may transmit the beacon signal or calibration signal using one or more antennas  321 . 
     It may be noted that, although the energy storage  302  is shown as charged by, and providing power to, WPRC  300 , the receiver may also receive its power directly from the rectifier  310 . This may be in addition to the rectifier  310  providing charging current to the energy storage  302 , or in lieu of providing charging. Also, it may be noted that the use of multiple antennas  320 ,  321 , and  322   a - 322   n  is one example of implementation, however the structure may be reduced to fewer antennas, such as one shared antenna. 
     In some embodiments, the control circuit  301  and/or the control module  303  can communicate with and/or otherwise derive device information from WPRC  300 . The device information can include, but is not limited to, information about the capabilities of the WPRC  300 , usage information of the WPRC  300 , power levels of the energy storage  302  of the WPRC  300 , and/or information obtained or inferred by the WPRC  300 . In some embodiments, a client identifier (ID) module  305  stores a client ID that can uniquely identify the WPRC  300  in a wireless power delivery environment. For example, the ID can be transmitted to one or more WPTSs in the encoded beacon signal. In some embodiments, WPRCs may also be able to receive and identify other WPRCs in a wireless power delivery environment based on the client ID. 
     A motion/orientation sensor  304  can detect motion and/or orientation and may signal the control circuit  301  to act accordingly. For example, a device receiving power may integrate motion detection mechanisms such as accelerometers or equivalent mechanisms to detect motion. Once the device detects that it is in motion, it may be assumed that it is being handled by a user, and may trigger a signal to the antenna array of the WPTS to either stop transmitting power and/or data, or to initiate wireless power and/or data transmission from the WPTS. The WPRC may use the encoded beacon or other signaling to communicate with the WPTS. In some embodiments, when a WPRC  300  is used in a moving environment like a car, train or plane, the power might only be transmitted intermittently or at a reduced level unless the WPRC  300  is critically low on power. 
     Additionally or alternatively, a WPRC  300  may include an orientation sensor which may sense a particular orientation of the WPRC  300 . An orientation of the WPRC  300  may affect how it receives wireless power from a WPTS. Thus, an orientation may be used to determine a best WPTS with which to pair. Motion/orientation sensor  304  may include only a motion sensor, only an orientation sensor, or may integrate both. Alternatively, two or more separate sensors may be used. Additionally or alternatively, a WPRC  300  may detect a direction of signals received via its antennas from one or more WPTSs to determine its orientation relative to the one or more WPTSs. Thus, in some embodiments, a WPRC  300  may be able to detect a relative orientation without a need for an orientation sensor. 
       FIG. 4  is a diagram illustrating an example wireless signal delivery environment  400  in accordance with embodiments described herein. The wireless signal delivery environment  400  includes WPTS  401 , a user operating WPRCs  402   a  and  402   b , and wireless network  409 . Although two WPRCs are depicted in  FIG. 4 , any number of WPRCs may be supported. WPTS  401  as depicted in  FIG. 4  can alternatively be implemented in accordance with WPTS  101  as depicted in  FIG. 1 . Alternative configurations are also possible. Likewise, WPRCs  402   a  and  402   b  as depicted in  FIG. 4  can be implemented in accordance with WPRCs  110   a - 110   c  of  FIG. 1 , or can be implemented in accordance with WPRC  300  as depicted in  FIG. 3 , although alternative configurations are also possible. 
     WPTS  401  may include a power supply  403 , memory  404 , processor  405 , interface  406 , one or more antennas  407 , and a networking interface device  408 . Some or all of the components of the WPTS  401  can be omitted, combined, or sub-divided in some embodiments. The networking interface device may communicate wired or wirelessly with a network  409  to exchange information that may ultimately be communicated to or from WPRCs  402   a  and  402   b . The one or more antennas  407  may also include one or more receivers, transmitters, and/or transceivers. The one or more antennas  407  may have a radiation and reception pattern directed in a space proximate to WPRC  402   a , WPRC  402   b , or both, as appropriate. WPTS  401  may transmit a wireless power signal, wireless data signal, or both over at least a portion of antennas  407  to WPRCs  402   a  and  402   b . As discussed herein, WPTS  401  may transmit the wireless power signal, wireless data signal, or both at an angle in the direction of WPRCs  402   a  and  402   b  such that the strength of the respectively received wireless signal by WPRCs  402   a  and  402   b  depends on the accuracy of the directivity of the corresponding directed transmission beams from at least a portion of antennas  407 . 
     A fundamental property of antennas is that the receiving pattern of an antenna when used for receiving is directly related to the far-field radiation pattern of the antenna when used for transmitting. This is a consequence of the reciprocity theorem in electromagnetics. The radiation pattern can be any number of shapes and strengths depending on the directivity of the beam created by the waveform characteristics and the types of antennas used in the antenna design of the antennas  407 . The types of antennas  407  may include, for example, horn antennas, simple vertical antenna, etc. The antenna radiation pattern can comprise any number of different antenna radiation patterns, including various directive patterns, in a wireless signal delivery environment  400 . By way of example and not limitation, wireless power transmit characteristics can include phase settings for each antenna and/or transceiver, transmission power settings for each antenna and/or transceiver, or any combination of groups of antennas and transceivers, etc. 
     As described herein, the WPTS  401  may determine wireless communication transmit characteristics such that, once the antennas and/or transceivers are configured, the multiple antennas and/or transceivers are operable to transmit a wireless power signal and/or wireless data signal that matches the WPRC radiation pattern in the space proximate to the WPRC. Advantageously, as discussed herein, the wireless signal, including a power signal, data signal, or both, may be adjusted to more accurately direct the beam of the wireless signal toward a location of a respective WPRC, such as WPRCs  402   a  and  402   b  as depicted in  FIG. 4 . 
     The directivity of the radiation pattern shown in the example of  FIG. 4  is illustrated for simplicity. It is appreciated that any number of paths can be utilized for transmitting the wireless signal to WPRCs  402   a  and  402   b  depending on, among other factors, reflective and absorptive objects in the wireless communication delivery environment.  FIG. 4  depicts direct signal paths, however other signal paths, including multi-path signals, that are not direct are also possible. 
     The positioning and repositioning of WPRCs  402   a  and  402   b  in the wireless communication delivery environment may be tracked by WPTS  401  using a three-dimensional angle of incidence of an RF signal at any polarity paired with a distance that may be determined by using an RF signal strength or any other method. As discussed herein, an array of antennas  407  capable of measuring phase may be used to detect a wave-front angle of incidence. A respective angle of direction toward WPRCs  402   a  and  402   b  may be determined based on respective distance to WPRCs  402   a  and  402   b  and on respective power calculations. Alternatively, or additionally, the respective angle of direction to WPRCs  402   a  and  402   b  can be determined from multiple antenna array segments  407 . 
     In some embodiments, the degree of accuracy in determining the respective angle of direction toward WPRCs  402   a  and  402   b  may depend on the size and number of antennas  407 , number of phase steps, method of phase detection, accuracy of distance measurement method, RF noise level in environment, etc. In some embodiments, users may be asked to agree to a privacy policy defined by an administrator for tracking their location and movements within the environment. Furthermore, in some embodiments, the system can use the location information to modify the flow of information between devices and optimize the environment. Additionally, the system can track historical wireless device location information and develop movement pattern information, profile information, and preference information. 
       FIG. 5  depicts an example embodiment of a wireless power delivery system  500 . The wireless power delivery system  500  may include one or more WPTSs such as WPTS  510 , one or more WPRCs such as WPRC  520 , and may also include access control services  530  that may run on one or more remote servers. Access control services  530  may be used to determine whether a WPRC, such as WPRC  520 , is authorized to receive wireless power from the WPTS  510 . In this way, for example, power may be delivered to only registered devices, to users who subscribe to a service, etc. In one embodiment, the WPTS  510  may transmit wireless power via a 2.4 GHz signal. In one embodiment, the access control services  530  may be running on one or more remote servers. 
     The WPRC  520  as depicted in  FIG. 5  may include a communication interface  522 . The communication interface  522  may be wired or wireless and may be used to communicate with WPTS  510 . WPRC  520  may further include a beacon generator and radio frequency (RF) power rectifier  523 . The beacon generator and RF power rectifier  523  may be coupled to the communication interface  522 . The beacon generator and RF power rectifier  523  may also be coupled through connections  524 - 1 - 524 - k  to antennas  525 - 1 - 525 - k , respectively. Although not depicted, the communication interface  522  may be additionally or alternatively coupled to antennas  525 - 1 - 525 - k  through connections  524 - 1 - 524 - k  or via other connections not depicted. Although nine antennas and corresponding connections are depicted in  FIG. 5 , any number of antennas may be used. As such, k may be any reasonable integer number. The WPRC  520  may transmit one or more beacons  540  via any portion of the antennas  525 - 1 - 525 - k  and may receive RF power from the WPTS  510  via any portion of the antennas  525 - 1 - 525 - k . Although not depicted, the WPRC  520  may communicate wirelessly with the WPTS  510  using any portion of the antennas  525 - 1 - 525 - k  via the communication interface  522 . The WPRC  520  may include load  521 , which may receive power sourced by RF power  550 . Load  521  may additionally or alternatively be coupled to WPRC  520 . 
     The WPTS  510  may include an access control software interface  511  that may be coupled to access control services  530 , a power supply  512 , a communication interface  513  that may be coupled to access control software interface  511  and to an antenna array controller  514 , and connections  515   a - 1 - 515   a - n ,  515   b - 1 - 515   b - n ,  515   c - 1 - 515   c - n , and  515   d - 1 - 515   d - n  coupling the antenna array controller  514  to antennas  516   a - 1 - 516   a - n ,  516   b - 1 - 5156 - n ,  516   c - 1 - 516   c - n , and  516   d - 1 - 516   d - n . The access controller software interface  511  may be responsible for managing power delivery scheduling and authentication. In one example, when a WPRC, such as WPRC  520 , is detected and identified, access controller software interface  511  may verify that WPRC  520  is authorized to receive power. Access controller software interface  511  may verify this by checking an identity of WPRC  520  against an internal list or a list stored in an external server, such as access control services running on remote servers  530 . The antenna array controller  514  may interface between power delivery management such as that provided by access control software interface  511 , and antenna controllers. In one example, a separate antenna controller may be included with each antenna of antennas  516   a - 1 - 516   a - n ,  516   b - 1 - 5156 - n ,  516   c - 1 - 516   c - n , and  516   d - 1 - 516   d - n . The antenna array controller  514  may manage antenna controllers to set transmit/receive modes, synchronize events for power delivery across the array of antennas, collect and/or process phase beacon payload data, etc. Although a particular number of antennas are depicted in WPTS  510 , any number of a plurality of antennas may be used. Similarly, the antennas are depicted in four groups, but any number of groups may be used. Antenna array controller  514  may interface with any portion of antennas  516   a - 1 - 516   a - n ,  516   b - 1 - 5156 - n ,  516   c - 1 - 516   c - n , and  516   d - 1 - 516   d - n  via any portion of corresponding connections  515   a - 1 - 515   a - n ,  515   b - 1 - 515   b - n ,  515   c - 1 - 515   c - n ,  515   d - 1 - 515   d - n  to receive one or more beacons  540  from WPRC  520  and may transmit RF power  550  to WPRC  520 . Although not depicted, the communication interface  513  may be additionally or alternatively coupled to any portion of antennas  516   a - 1 - 516   a - n ,  516   b - 1 - 5156 - n ,  516   c - 1 - 516   c - n , and  516   d - 1 - 516   d - n  through connections  515   a - 1 - 515   a - n ,  515   b - 1 - 515   b - n ,  515   c - 1 - 515   c - n ,  515   d - 1 - 515   d - n  or via other connections not depicted. 
     In the design depicted in  FIG. 5 , a point-to-point architecture may be employed to couple the antennas to the antenna array controller  514 . As such, as the number of antennas increases, the number of connections between the antennas and the antenna array controller  514  increases. In some embodiments, increasing a frequency of the wireless power signal from, for example, 2.4 GHz to 24 GHz may require additional antennas. 
     For a given aperture size for the WPTS and WPRC, delivery of power scales by the square of the frequency of the wireless power signal at a given distance. For example, power received at the WPRC, P r  is as follows: 
     
       
         
           
             
               
                 
                   
                     
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     for a transmitted power of P t , a WPTS with an area of A t , a WPRC with an area of A r  that is separated from the WPTS by a distance R, a wavelength of the wireless power signal λ, an aperture efficiency for the WPTS of ε t , and an aperture efficiency of the WPRC of ε r . Thus, the ratio of the received power at the WPRC to the power transmitted by the WPTS is as follows: 
     
       
         
           
             
               
                 
                   
                     
                       
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     which is proportional to the square of the frequency of the transmitted power. Therefore, by increasing the frequency of the power transmitted by the WPTS, for example from 2.4 GHz to 5 GHz or 24 GHz, the power received at the WPRC may be increased. 
       FIG. 6  depicts another example embodiment of a wireless power delivery system  600 . The wireless power delivery system  600  may include one or more WPTSs such as WPTS  610 , one or more WPRCs such as WPRC  620 , and may also include access control services  630  that may run on one or more remote servers, such as described above with respect to access control services  530  depicted in  FIG. 5 . In one embodiment, the WPTS  610  may transmit wireless power via a 24 GHz signal. In one embodiment, the access control services  630  may be running on one or more remote servers. 
     WPRC  620  depicted in  FIG. 6  may be similar to the WPRC  520  depicted in  FIG. 5  and may include similar components and operate similarly as described above. 
     WPTS  610  depicted in  FIG. 6  may include access control software interface  611 , power supply  612 , and communication interface  613  which may operate similarly as described for access control software interface  511 , power supply  512 , and communication interface  513  as depicted in  FIG. 5 . 
     WPTS  610  may also include an antenna array controller  614  that may use daisy-chain buses  615 - 1 - 615 - m  to communicate with antenna controllers  617 - 1 - 1 - 617 - 1 - n  and antenna controllers  617 - m - 1 - 617 - m - n . Although only two daisy chain buses are depicted in  FIG. 6 , any number of daisy-chain buses may be used. Each antenna controller  617  may be coupled to any plurality of antennas  616 . For example, as depicted in  FIG. 6 , each antenna controller  617  may be coupled to four antennas  616 . Furthermore, although eight antenna controller  617  are depicted connected to each daisy chain bus  615 , any number of antenna controllers  617  may be connected. 
     The antenna controllers  617  may be placed relatively close to the respective antennas  616  coupled to it. Antenna controllers  617 , which will be explained in more detail below, may be small, simple circuits that may require minimal control and synchronization from antenna array controller  614  via a daisy-chain bus  615 . A configuration such as that depicted in  FIG. 6  may allow for a WPTS to have thousands of antennas without significant increases to cost. For example, a 30 cm×30 cm WPTS may be produced with 4,608 antennas may be manufactured without significant cost. 
       FIG. 7  is a diagram of an antenna array controller  720  coupled to a plurality of antenna controllers  760 - 1 - 760 - n  and a clock generator  710  such as may be used in WPTS  610  depicted in  FIG. 6 . Antenna array controller  720  may provide a reference clock to each of the antenna controllers  760 - 1 - 760 - n  via a reference clock differential pair  740 . Antenna array controller  720  may also supply command messages via command message differential pair  750 . As will be further detailed below, antenna array controller  720  may control antenna controllers  760 - 1 - 760 - n  via a daisy-chain differential pair  730 . Although six antenna controllers  760 - 1 - 760 - n  are depicted, any number of antenna controllers  760  may be used. 
     The command message differential pair  750  may transmit a 1-bit single-ended control signal synchronous with the undivided reference clock and may be used to synchronize the phase locked loops (PLLs) of multiple antenna controllers. The PLL/voltage controlled oscillator (VCO)  810  of an antenna controller depicted in  FIG. 8  will be described in greater detail below. Command messages sent via the command message differential pair  750  may be clocked by a version of the reference clock generated by clock generator  710  that is divided down by an integer. A message bit rate between, for example, 40-50 MBits/sec may be supported by dividing the reference clock by an appropriate integer. Each antenna controller  760 - 1 - 760 - n  may be individually configured to use either the positive edge or the negative edge of the reference clock. 
     Most high-level state information may be managed by antenna array controller  720 . The antenna array controller  720  may send messages to the antenna controllers  760 - 1 - 760 - n  that may cause one or more state machines within the antenna controllers  760 - 1 - 760 - n  to automatically sequence through a series of states. Some of these messages may include, for example, a “create a first phase beacon slot” message. 
     Command messages may be variable length and may be broadcast by the antenna array controller  720  via the command message differential pair  750  to the individual antenna controllers  760 - 1 - 760 - n  using a single command message signal that may be synchronized with the reference clock transmitted via the reference clock differential pair  740 . By synchronizing command message to the reference clock, a separate clock line may be avoided to clock the commands and it allows commands to be used to ensure that all antenna controllers  760 - 1 - 760 - n  are phase-synchronized with each other. Although not depicted, the reference clock differential pair  740  and command message differential pair  750  may be propagation-delay matched. The data rate on the command message differential pair  750  may be configurable to be, for example, ½, ¼, ⅙, or ⅛ the rate of the reference clock. Other rates may be possible. 
     One or more messages may be passed from the antenna controllers  760 - 1 - 760 - n  to the antenna array controller  720  via the daisy chain differential pair  730 . A single signal may start at the antenna array controller  720  and may pass through a delay chain of a plurality of stages per each antenna controller  760 , and return to the antenna array controller  720 . Each antenna controller  760  may include, for example, approximately 22 stages introducing delays. The daisy chain differential pair  730  may be synchronous with the reference clock. A data rate on the daisy chain differential pair  730  may be configurable to be, for example, ½, ¼, ⅙, or ⅛ the rate of the reference clock. Other rates may be possible. 
     To initialize a WPTS sequence order, the antenna array controller  720  may send a sequencing message via the daisy chain differential pair  730  to the first antenna controller  760 - 1 . Antenna controller  760 - 1  may set its index to an index included in the sequencing message. The antenna controller  760 - 1  may increment the index included in the sequencing message and then forward the sequencing message to the next antenna controller  760 - 2 . Antenna controller  760 - 2  may set its index to the index in the sequencing message it received, which was incremented by antenna controller  760 - 1 . Antenna controller  760 - 2  may increment the index included in the sequencing message again and the forward the sequencing message onward. This process repeats until the sequencing message has returned to the antenna array controller  720 . In this way, all of the antenna controllers  760 - 1 - 760 - n  may be enumerated with an index and the antenna array controller may determine how many antenna controllers  760  are in the daisy chain based on the value of the index returned. 
     Although  FIG. 7  depicts differential pairs and the description above refers to these differential pairs, command message differential pair  750 , reference clock differential pair  740 , and daisy chain differential pair  730  need not be differential pairs, but may be any form of bus that transmits any suitable signals across the bus. 
       FIG. 8  is a diagram of an antenna management unit (AMU)  800 . In a configuration such as that depicted in  FIG. 6  wherein an antenna controller  617  is coupled to four antennas  616 , the antenna controller  617  may include four AMUs  800 . In this scenario, the antenna controller  617  may include a single PLL/VCO  810  that may be shared across the four AMUs  800 . In some embodiments, as frequencies increase, it may be desirable to have more AMUs  800  per antenna controller  617  to drive correspondingly more antennas  616 . The PLL/VCO  810  may be coupled to a phase shifter  821  and a mixer  860 . 
     In a receive mode, the switch  830  may be set to couple the antenna  840  to low noise amplifier (LNA)  850 . A beacon signal received from a WPRC may be received at the antenna  840 , amplified by the LNA  850 , and down-converted to an intermediate frequency (IF) by the mixer  860 . The down-converted signal may then be passed through an IF section  871  for filtering and/or signal conditioning and output to an analog-to-digital converter (ADC)  872  where it may be digitized for beacon phase and/or received signal strength (RSS) detection  873 . 
     In a transmit mode, the switch  830  may be set to couple power amplifier  822  to antenna  840 . A signal from the PLL/VCO  810  may be driven to the antenna  840  by the power amplifier  822  through the phase shifter  821  to deliver wireless power and/or data to a WPRC. The phase shifter  821  may be programmed to the complex conjugate of a received phase beacon signal. AMU  800  may be used in conjunction with one or more additional AMUs  800  respectively driving one or more additional antennas  840  to directionally focus wireless power and/or data to one or more WPRCs. 
       FIG. 9  is a timing diagram that depicts a frequency domain duplexing (FDD) and time domain duplexing (TDD) exchange of timing beacons, phase beacons, and wireless power transmission. While a WPTS may be transmitting wireless power, such as wireless power transmission  931 , using a particular power transmission frequency  930 , a first WPRC may transmit a timing beacon  911  using another frequency  910  that is offset from the power transmission frequency  930 . The frequency  910  used for transmission of the timing beacon  911  may be offset from the power transmission frequency  930  to avoid self-jamming by the wireless power transmission  931  and to enable asynchronous detection of timing beacon  911  while the wireless power transmission  931  is being transmitted. Using a timing beacon that is transmitted at a frequency that is offset from a power transmission frequency also enables the use of multiple power transmitters. The timing beacon  911  may be encoded so that the WPTS may determine if the WPRC that transmitted the timing beacon  911  is registered to that WPTS. Basing signal and power exchange on a timing beacon that is transmitted by the WPRC rather than basing signal and power exchange on a schedule controlled by the WPTS, the WPRC may be able to stay in a deep sleep until the WPRC has an actual need for power. This may reduce overhead associated with frequent communications that were present in conventional systems that employed a schedule controlled by the WPTS. 
     Once the timing beacon  911  has been detected by the WPTS, the WPTS may stop transmitting wireless power during the first beacon slot  937  and wait for the first phase beacon  921  received via phase beacon frequency  920 . Phase beacon frequency  920  may be the same as power transmission frequency  930  or may be different. The WPTS may use the first phase beacon  921  for actual phase detection. Using the detected phase, the WPTS may directionally focus wireless power transmission  933  at a location of the WPRC. First phase beacon  921  may also be encoded to convey data to the WPTS such as the ID of the WPRC, state of charge of the WPRC, etc. One or more subsequent phase beacons  922  may be transmitted and the WPTS may halt power transmission during one or more subsequent beacon slots  938  based on the timing established by the timing beacon  911 . The one or more subsequent beacon slots  938  may additionally or alternatively be scheduled via communication between the WPTS and the WPRC. The subsequent phase beacon  922  may be used to detect phase and directionally focus wireless power transmission  934  at a location of the WPRC, which may now be a new location due to the WPRC having moved or due to changes in the environment. A timing beacon  912  from the same WPRC or from a new WPRC may be transmitted using the timing beacon frequency  910 , followed by a phase beacon  923  using the phase beacon frequency  920 , and the WPTS may receive the phase beacon  923  during the associated phase beacon slot  939  and use the phase beacon  923  to directionally focus wireless power transmission  936  at a location corresponding to the phase beacon  923 . 
     While power delivery may be initiated by the WPRC through the timing beacon, in some embodiments, the WPTS may have some control over beacon scheduling through communication with the WPRC to set intervals between subsequent beacons. If large changes in the phase pattern from a WPRC&#39;s phase beacon are detected, the WPTS can infer that this receiver is likely moving. The WPTS can subsequently request more frequent phase beacons and send shorter power slots between phase beacons for more accurate tracking of the WPRC. Conversely, if phase patterns for a phase beacon are relatively static, the WPTS can infer that this WPRC is more or less stationary and may reduce the number of phase beacons and may increase a power slot duration of a wireless power transmission. In this way, the efficiency of power delivery to static WPRCs may be increased by reducing beacon overhead, while safe power delivery may be maintained for WPRCs which may be moving more rapidly. 
     In some embodiments, an output power of a timing beacon or a phase beacon may be adjusted based on the distance of the WPRC from the WPTS. For example, in one embodiment, a WPRC at a closer distance could reduce the output power of its beacon to consume less energy while staying within the dynamic range of the WPTS. This could be accomplished through feedback from the WPTS, which may infer the distance based on the average magnitude of the last beacon signal, or by the WPRC itself based on the magnitude of the power delivered in the last cycle. A variable beacon power enables conservation of WPRC power and reduces dynamic range requires of the WPTS. 
     In some embodiments, by scavenging ambient RF energy, WPRCs with a fully discharged battery are able to accumulate enough energy to send a beacon and initiate power transfer from the WPTS. This enables a WPRC to not require direct/wired charging. In some embodiments, by reaching a deeper depth of energy discharge, a WPRC equipped with certain battery types may be operate with a longer lifetime. A WPRC capable of such harvesting of ambient RF energy may use a super capacitor for primary energy storage instead of a battery. 
     In some embodiments, a WPTS may also adjust the power level of its wireless power transmissions. By sensing a received signal strength indicator (RSSI) of a beacon signal across an antenna array of the WPTS, the WPTS can infer a distance between the WPTS and the WPRC. Combining this information with knowledge of the power requirements of the WPRC and the expected link budget, the WPTS can increase or decrease its output power to regulate the amount of power received by the WPRC. This avoids potentially exposing WPRCs that are close to the WPTS to excessive amounts of energy that could damage the rectifier or unnecessarily interfere with data communications. 
       FIG. 10  depicts an example of how a WPRC payload list may propagate around a daisy chained arrangement  1000  of antenna controllers  1020 - 0 - 1020 - 5  and an antenna array controller  1010 . A payload list may indicate information encoded in a phase beacon, such as a WPRC ID, state of charge, wireless sensor data, a quantity of received RF power in a previous cycle, or other information depending on the application. In one example, after a phase beacon slot, such as first beacon slot  937  depicted in  FIG. 9 , the antenna array controller  1010  may determine which WPRC transmitted the phase beacon and may also determine how many antennas received the phase beacon. This information may be collected by creating a list of received WPRC IDs and an associated count in a payload list. This payload list may be forwarded on the daisy chain  1040  to a next antenna controller  1020  or back to the antenna array controller  1010 . 
     In one example, a first antenna controller, such as antenna controller  1020 - 0 , may start the payload list propagation by creating an empty list  1030 - 0 . Antenna controller  1020 - 0  may, for example, have a chip ID of zero. In another example, the antenna array controller  1010  may start the payload list propagation by passing an empty list  1030 - 0  to the first antenna controller  1020 - 0  such as depicted in  FIG. 10 . In the example payload list  1030 - 0 - 1030 - 6  depicted in  FIG. 10 , a first column may include a “p” as an indication of a payload entry. In the example, a second column may include a “1” corresponding to the final payload entry in the list to indicate an end of the list. In the example, a third column may include a count reflecting how many antennas at which a corresponding payload was received. In the example, a fourth column may indicate unique values of the payloads received. The list may be passed from one antenna controller to the next antenna controller and edited by each antenna controller to update the list to reflect the received payload data by each antenna controller, such as received WPRC IDs, along the way. The list may, for example, reflect a WPRC ID and a corresponding count reflecting how many antennas on which the WPRC ID was received. Each of antenna controllers  1020 - 0 - 1020 - 5  may increment the corresponding counts of the WPRC IDs received at each of its antennas. Thus, in the example depicted in  FIG. 10 , the respective received payload information  1021 - 0 - 1021 - 5  for antenna controllers  1020 - 0 - 1020 - 5  each reflects four entries, each entry corresponding to a WPRC ID received at one of four antennas coupled to each antenna controller, such as shown in the WPTS  610  depicted in  FIG. 6 . 
     As depicted in  FIG. 10 , antenna controller  1020 - 0  may receive WPRC ID 0xEF001 at three antennas and WPRC ID 0xDD100 at one antenna. Thus, antenna controller  1020 - 0  may update the payload list  1030 - 1  to add two entries to indicate a count of three for 0xEF001 and a count of one for 0xDD100. Antenna controller  1020 - 1  may receive WPRC ID 0xEF001 at all four of its antennas. Thus, antenna controller  1020 - 1  increment the count for 0xEF001 by four and update the payload list  1030 - 2  to indicate a count of seven for 0xEF001 and a count of one for 0xDD100. Antenna controller  1020 - 2  may receive WPRC ID 0xEF001 at three of its antennas and WPRC ID 0x45f32 at one of its antennas. Thus, antenna controller  1020 - 2  may increment the count for 0xEF001 by three and add WPRC ID 0x45f32 to the payload list. The updated payload list  1030 - 3  may now indicate a count of ten for 0xEF001, a count of one for 0xDD100, and a count of one for 0x45f32. Antenna controller  1020 - 3  may receive WPRC ID 0xEF001 at all four of its antennas. Thus, antenna controller  1020 - 3  may increment the count for 0xEF001 by four and update the payload list  1030 - 4  to indicate a count of fourteen for 0xEF001, a count of one for 0xDD100 and a count of one for 0x45f32. Antenna controller  1020 - 4  may also receive WPRC ID 0xEF001 at all four of its antennas. Thus, antenna controller  1020 - 4  may increment the count for 0xEF001 by four and update the payload list  1030 - 5  to indicate a count of eighteen for 0xEF001, a count of one for 0xDD100 and a count of one for 0x45f32. Antenna controller  1020 - 5  may receive WPRC ID 0xEF001 at three of its antennas and WPRC ID 0x45f32 at one of its antennas. Thus, antenna controller  1020 - 5  may increment the count for 0xEF001 by three and increment the count for WPRC ID 0x45f32 by one. The updated payload list  1030 - 6  may now indicate a count of twenty-one for 0xEF001, a count of one for 0xDD100, and a count of two for 0x45f32. Payload list  1030 - 6  may then be returned to the antenna array controller  1010  where it is able to determine what WPRC IDs were received and associated counts. 
     Typically, the payload list  1030 - 6  should only contain a single entry with a count equal to the number of antennas, such as twenty-four in the example depicted in  FIG. 10 , indicating that the same entry was received by all antennas from the WPRC expected to beacon. More than one entry, such as that depicted in  FIG. 10 , may indicate a beacon collision or another type of failure during phase beacon reception. It should be noted that the payload received and the payload lists depicted in  FIG. 10  are examples only and are not limiting in any way. 
     In one example, each of antenna controllers  1020 - 0 - 1020 - 5  may include four AMUs, such as AMU  800  depicted in  FIG. 8 . In some embodiments, if any of the AMUs were unable to parse the WPRC payload out of the phase beacon, then they may add a special reserved WPRC value to the payload list which represents that no WPRC payload was received. 
     In another example, a payload list may not be allowed to contain duplicate WPRC payload entries. Instead, the associated count for the entry already in the payload list will be incremented appropriately, such as described in the examples above and as depicted in  FIG. 10 . In one example, a last received WPRC payload message in the payload list may be flagged with a “last flag” to indicate the end of the payload list. As described above, in the example depicted in  FIG. 10 , the “last flag” for the last entry in the payload list  1030 - 0 - 1030 - 6  may be indicated by a single bit set to “1” in the second column. 
       FIG. 11  depicts an example method that may be performed, for example, by an antenna controller of a WPTS to propagate a payload list of received WPRC information via an encoded phase beacon. At  1110 , a payload list is initialized. As described above, a first antenna controller may be responsible for initializing the payload list or the antenna array controller may initialize the list. At  1120 , one or more phase beacon payloads are received. As described above with respect to  FIGS. 6 and 10 , in one example, an antenna controller may include four AMUs and thus may receive four corresponding beacon payloads. At  1130 , it may be determined whether any of the received phase beacon payloads are in the payload list. If a received phase beacon payload is in the payload list, at  1141  the antenna controller may update the list by incrementing the count for that particular phase beacon payload appropriately. If a received phase beacon payload is not in the payload list, at  1142  the antenna controller may add the phase beacon payload to the list with an appropriate count corresponding to the number of antennas at which the phase beacon payload was received. In one example, the phase beacon payloads may be equivalently viewed as being received at a number of AMUs. In one example, if there is no more room in the payload list, the received phase beacon payload may be discarded. In another example, the payload list may be grown to accommodate a new received phase beacon payload by adding a new row to the payload list. If the payload list is grown, a “last flag,” such as that described above with respect to  FIG. 10 , may be shifted down to the newly added row. At  1143 , the current antenna controller may forward the payload list to a next antenna controller if the current antenna controller is not the last antenna controller in the daisy chain. If the current antenna controller is the last in the daisy chain, the current antenna controller may forward the payload list to the antenna array controller which may then receive a payload list that has been aggregated across all of the antenna controllers on the daisy chain. 
     It should be noted that the example method and particular order of steps depicted in  FIG. 11  is not meant to be limiting. The steps as depicted in  FIG. 11  may be rearranged, combined, omitted, sub-divided, or otherwise modified and still fall within the scope of the embodiments described herein. 
       FIG. 12  depicts field pocket sizes corresponding to frequencies/wavelengths used to transmit directional wireless power from a WPTS to a WPRC that is 1 meter away. As shown in  FIG. 12 , as the frequency of the transmitted wireless power increases, the field pocket size decreases. As such, a WPTS transmitting wireless power at 24 GHz is capable of focusing wireless power on a smaller area than the area achievable at lower frequencies such as 5.8 GHz and 2.4 GHz. Additionally, by focusing power on a smaller area, a WPTS transmitting wireless power at 24 GHz may be able to deliver more power to a WPRC. 
     Although features and elements are described above in particular combinations, one of ordinary skill in the art will appreciate that each feature or element can be used alone or in any combination with the other features and elements. In addition, the methods described herein may be implemented in a computer program, software, or firmware incorporated in a computer-readable medium for execution by a computer or processor. Examples of computer-readable media include electronic signals (transmitted over wired or wireless connections) and computer-readable storage media. Examples of computer-readable storage media include, but are not limited to, a read only memory (ROM), a random access memory (RAM), a register, cache memory, semiconductor memory devices, magnetic media such as internal hard disks and removable disks, magneto-optical media, and optical media such as CD-ROM disks, and digital versatile disks (DVDs). A processor in association with software may be used to implement a WPTS or WPRC.