Patent Publication Number: US-10333201-B2

Title: Multi-antenna wearable device

Description:
TECHNICAL FIELD 
     The present disclosure generally relates to multi-antenna devices, and, more particularly, although not necessarily exclusively, to using a common ground plane conductor for multiple antennas. 
     BACKGROUND 
     As electronic devices decrease in size, the area on a printed circuit board to configure electronic components of the electronic device becomes increasingly limited. The limited area may affect electronic devices including multiple antennas for multi-band communication with external systems and devices. For example, different antennas may have different layout requirements, and using multiple different antennas in a single device may affect the size of the device. 
     SUMMARY 
     In some aspects of the present disclosure, a monitoring device may include a high-frequency antenna and a low-frequency antenna operable in different frequency ranges to wirelessly communicate biological measurements obtained by a sensor to an external computing device proximate to the monitoring device. The monitoring device may include a metal ground plane conductor formed on a printed circuit board within a housing of the monitoring device. The metal ground plane conductor may include a contiguous metal surface that defines channels corresponding to gaps in the contiguous metal surface. To reduce eddy currents caused by the metal ground plane conductor during low-frequency communication, each of the channels may include at least one capacitor acting as an open circuit when the low-frequency antenna is operating in a low-frequency range. In some aspects, the channels may be dimensioned to, themselves, act as the capacitor. In other aspects, discrete capacitors may be positioned on the metal ground plane conductor spanning opposite sides of the channels. 
     In one aspect, a wearable monitoring device comprises a housing. The wearable monitoring device also comprises a PCB disposed in the housing and including a first wireless communication device and a second wireless communication device disposed on the PCB. The wearable monitoring device also comprises a biological sensor communicatively coupled to the PCB. The wearable monitoring device also comprises a first antenna communicatively coupled to the first wireless communication device and tuned for a first frequency range. The wearable monitoring device also comprises a second antenna communicatively coupled to the second wireless communication device and tuned for a second frequency range. The wearable monitoring device also comprises a ground plane conductor disposed on the PCB and including a contiguous metal surface defining a plurality of channels extending inward from a perimeter of the contiguous metal surface. The wearable monitoring device also comprises at least one capacitor for each of the channels. Each capacitor is sized to operate substantially as a short circuit in the first frequency range and to operate substantially as an open circuit in the second frequency range. The first frequency range and the second frequency range do not overlap. 
     In another aspect, a method includes providing a printed circuit board (“PCB”). The method also includes forming a ground plane conductor on the PCB. The ground plane conductor has a contiguous metal surface defining one or more channels extending inward from a perimeter of the contiguous metal surface. The channels are gaps in the contiguous metal surface of the ground plane conductor. The method also includes forming a high-frequency antenna and a low-frequency antenna. The high-frequency antenna is tuned for a first frequency range and the low-frequency antenna tuned for a second frequency range that does not overlap the first frequency range. The method also includes communicatively coupling the high-frequency antenna to the ground plane conductor. 
     In another aspect, a method includes attaching a monitoring device to skin of a patient. The monitoring device includes a sensor and a multi-antenna device coupled to a PCB. The multi-antenna device includes a high-frequency antenna tuned for a first frequency range, a low-frequency antenna tuned for a second frequency range, and a ground plane conductor having a contiguous metal surface defining a plurality of channels. The plurality of channels are gaps in the metal surface of the ground plane conductor. The plurality of channels are operable substantially as a short circuit in the first frequency range and operable substantially as an open circuit in the second frequency range. The method also includes positioning a computing device within coupling range of the monitoring device. The method also includes using the computing device to wirelessly communicate with the monitoring device to obtain information from the sensor using one of the high-frequency or low-frequency antennas. 
     These illustrative examples are mentioned not to limit or define the scope of this disclosure, but rather to provide examples to aid understanding thereof. Illustrative examples are discussed in the Detailed Description, which provides further description. Advantages offered by various examples may be further understood by examining this specification. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated into and constitute a part of this specification, illustrate one or more certain examples and, together with the description of the example, serve to explain the principles and implementations of the certain examples. 
         FIG. 1A  is a graphical illustration of an example of a monitoring device communicatively coupled to a handheld device at a close range using a multi-antenna device according to some aspects of the present disclosure. 
         FIG. 1B  is a graphical illustration of the monitoring device communicatively coupled to the handheld device at a greater range using the multi-antenna device according to some aspects of the present disclosure. 
         FIG. 2A  is a cross-sectional side view of a printed circuit board supporting a multi-antenna device according to some aspects of the present disclosure. 
         FIG. 2B  is a semi-transparent top-down view of a multi-device antenna disposed on the printed circuit board of  FIG. 2A  according to aspects of the present disclosure. 
         FIG. 3  is a semi-transparent view of an example configuration for a multi-antenna device disposed on a printed circuit board according to some aspects of the present disclosure. 
         FIG. 4  is a semi-transparent top-down view of capacitors disposed on the ground plane conductor of a multi-antenna device according to some aspects of the present disclosure. 
         FIG. 5  is a semi-transparent top-down view of an example configuration for the ground plane conductor of a multi-antenna device according to some aspects of the present disclosure. 
         FIG. 6  is a flow chart of a process for manufacturing a multi-antenna device according to aspects of the present disclosure. 
         FIG. 7  is a flow chart of a process for using a monitoring device including a multi-antenna device according to aspects of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Certain aspects and examples of the present disclosure relate to compact devices having both high-frequency and low-frequency antennas proximate to a ground plane conductor disposed on a printed circuit board (“PCB”). In one example, a multi-antenna device includes a ground plane conductor, a low frequency antenna, and a high-frequency antenna. In this example, the ground plane conductor includes a metal surface that improves performance of the high-frequency antenna during high-frequency communications. But, the metal surface generates eddy currents that degrade the performance of the low-frequency antenna during low-frequency communications. Thus, to reduce the effect of eddy currents generated by the ground plane conductor during low-frequency communications, the ground plane conductor defines several channels that extend from the outer edge of the ground plane conductor towards its center. The widths of the channels have been sized to create a capacitance across each channel. The capacitances of the channels have been selected such that, during high-frequency transmission or reception, they operate as short circuit, thus apparently eliminating the channels. But at low frequencies, the capacitances operate as open circuits thereby reducing the apparent size of the ground plane conductor and reducing the impact of eddy currents. 
     While the illustrative example above sizes the channels to create suitable capacitances, in some aspects, multi-antenna devices may include a ground plane conductor defining channels that are bridged by one or more capacitors that have been sized to operate as a short circuit in a high-frequency range and an open circuit in a low-frequency range. A high-frequency antenna tuned for the high-frequency range and a low-frequency antenna tuned for the low-frequency range may be communicatively coupled to the PCB through the ground plane conductor to allow the multi-antenna device to communicate with external devices in both the high-frequency range and the low-frequency range. In some aspects, the ground plane conductor may include a contiguous, two-dimensional surface defining the channels. The channels may be non-intersecting and may extend inward from a perimeter of the ground plane conductor. In some aspects, the dimensions of the channels (e.g., size, shape) may be defined to act as a short circuit or open circuit during operation of the high-frequency antenna and the low-frequency antenna. For example, channels having a rectangular shape and a large surface area may provide greater capacitance to act as an open circuit at low frequencies and as a short circuit at high frequencies. In another example, channels having an interdigital, or crenellated, shape may provide similarly enhanced capacitance. 
     In some aspects, the multi-antenna device may serve as a wireless communication component of a device, such as a monitoring device. In some aspects, the monitoring device may include one or more invasive or non-invasive sensors. The sensors may be incorporated onto the same PCB as the multi-antenna device. In some aspects, the PCB may be a multilayer PCB to allow space to compact a greater number of components to the PCB without compromising a compact design of the monitoring device. In some aspects, the components of the multi-antenna device may be distributed within the PCB. For example, the high-frequency antenna may be positioned or disposed on, or otherwise in communication with, a first layer of the PCB, the low-frequency antenna may be positioned or disposed on, or otherwise in communication with, a second layer of the PCB, and the ground plane conductor may be positioned or disposed on, or otherwise in communication with, a third layer of the PCB. 
     Detailed descriptions of certain examples are discussed below. These illustrative examples are given to introduce the reader to the general subject matter discussed here and are not intended to limit the scope of the disclosed concepts. The following sections describe various additional aspects and examples with reference to the drawings in which like numerals indicate like elements, and directional descriptions are used to describe the illustrative examples but, like the illustrative examples, should not be used to limit the present disclosure. The various figures described below depict examples of implementations for the present disclosure, but should not be used to limit the present disclosure. 
     Various aspects of the present disclosure may be implemented for wireless communication in various scenarios.  FIGS. 1A and 1B  illustrate a monitoring device  100  positioned on human skin  102 . In some aspects, the monitoring device  100  may be a biomedical device for measuring biological parameters of a patient, such as glucose levels of a diabetic patient. For example, the monitoring device  100  may be a wearable device attached to the skin  102  of a patient by an adhesive layer on the monitoring device&#39;s  100  housing, a band (not shown), interference between an injected sensor and the skin  102  (for invasive monitoring devices), or by other suitable attaching means. In another example, the monitoring device  100  may be an implantable device implanted into the skin  102 . In some aspects, the monitoring device  100  may include one or more invasive or non-invasive sensor devices for measuring the biological parameters of a patient and may use the multi-antenna device according to aspects of the present disclosure to communicate the parameter measurements to an external device  104 . 
     The monitoring device  100  may be compact in size for placement on the patient&#39;s skin  102 . In some aspects, the compact nature of the monitoring device  100  may allow for the monitoring device  100  to remain on the skin  102  for an extended period of time to continuously monitor the biological parameters of the patient with minimal discomfort. For example, the monitoring device  100  may be positioned on a patient&#39;s arm and remain in place on the arm for several days to provide measurements of the patient&#39;s biological parameters at regular intervals (e.g., every minute, every hour, etc.). The monitoring device&#39;s  100  compact nature may also provide an increased number of areas on the patient&#39;s skin  102  that the monitoring device  100  may be placed. For example, the monitoring device  100  may be sized for placement on the skin  102  of a patient&#39;s limb, such as an arm or leg, or on a patient&#39;s stomach. In other examples, the monitoring device  100  may be sufficiently compact for placement on a smaller body part, such as a patient&#39;s hand or finger. In some aspects, the monitoring device  100  may include a housing having a circular or other rounded cross-sectional shape and having a diameter (or diameter-like measurement through the center of the shape for non-circular, rounded shapes) measuring less than approximately 2 inches (or approximately 5 centimeters). Similarly, in another example, the monitoring device&#39;s  100  housing may have a polygonal shape with a width or length measuring less than approximately 2 inches (or approximately 5 centimeters). 
     In some aspects, the external device  104  may include a computing device having one or more antenna devices compatible with the multi-antenna device of the monitoring device  100  for allowing wireless communication between the monitoring device  100  and the external device  104 . In some aspects, the external device  104  may be a handheld computing device, such as a smartphone, personal digital assistant, or tablet. In other aspects, the external device  104  may represent any computing device having communication means for wireless communication, such as RFID, NFC, BlueTooth, or a wireless local area network (WLAN) device, with the monitoring device  100 , including, but not limited to a desktop computer, a laptop, or a wearable device (e.g., a smartwatch). In additional and alternative aspects, the external device  104  may include a processor for analyzing measurements transmitted from the monitoring device  100  and/or a database for storing such measurement. 
     In  FIG. 1A , the external device  104  is shown as positioned in short-range proximity to the monitoring device  100 . Arrows  106  represent a communicative coupling of the monitoring device  100  and the external device  104  for wireless communication between the devices. In some aspects, the coupling range for communicatively coupling the monitoring device  100  and the external device  104  may include a proximity between 0 and 25 centimeters. Such a range may be suitable for certain short-range communication technologies, such as RFID or NFC, using a low-frequency antenna. In  FIG. 1B , the external device  104  is shown as positioned farther away from the monitoring device  100  than the external device  104  shown in  FIG. 1A . Arrows  108  represent a communicative coupling of the monitoring device  100  and the external device  104  for wireless communication at a farther range. In some aspects, the coupling range for communicatively coupling of the monitoring device  100  and the external device  104  include a proximity between 0 and 120 meters. While in some examples, RFID and NFC may not be capable of communicating over longer ranges, other communication technologies may be used, such as BlueTooth or WiFi, which may use a high-frequency antenna. In some aspects, the frequency at which the monitoring device  100  may wirelessly communicate with the external device  104  may be directly proportional to the coupling range between the devices  100 ,  104 . For example, the communicative coupling of the monitoring device  100  and the external device  104  at a short-range proximity as depicted by the arrows  106  may allow for communication at a lower frequency than the frequency of communication between the monitoring device and the external device  104  coupled at the greater range, as depicted by the arrows  108 . In some aspects, the multi-antenna device may include multiple antennas, each configured for wireless communication at varying frequency ranges. The multiple antennas may allow the multi-antenna device to facilitate wireless communication at both the short-range proximity depicted by the arrows  106  and the longer-range proximity depicted by the arrows  108   
       FIGS. 2A and 2B  depict a PCB  200  that may incorporate the electrical components of the monitoring device  100  of  FIGS. 1A and 1B  according to some aspects.  FIG. 2A  is a cross-sectional side view of the PCB  200  and  FIG. 2B  shows a multi-device antenna disposed on the PCB  200 . The PCB  200  may be internal to a housing  202  of the monitoring device  100 . In some aspects, the housing  202  may serve as the housing for all components of the monitoring device  100  of  FIG. 1 . In other aspects, the housing  202  may house only the PCB  200  and subset of monitoring device  100  components that are physically disposed on the PCB  200 . Although the housing  202  is depicted in  FIG. 2A  as having a rectangular cross-sectional shape, the housing  202  may have any shape without departing from the scope of the present disclosure. For example, the housing  202  may have a rounded surface, a flat surface, or another non-rectangular cross-sectional shape. The housing  202  may be made of any suitable material for housing the PCB  200 . Non-limiting examples of materials that may be suitable for the housing  202  include molding material, polyethylene, polyvinyl chloride (“PVC”), polypropylene, nylon, polyurethane, polycarbonate, steel, aluminum, and other materials for forming the housing. In some aspects, at least one surface of the housing  202  may be thin to allow radio frequencies from the multi-antenna device to be transmitted to and received from wireless communication devices external to the housing  202 . 
     In this example, the PCB  200  is a multi-layer PCB including three layers  200   a - c  as shown in  FIG. 2A . Each layer  200   a - c  may include conductive traces, or other features etched into the surface, to incorporate the monitoring device&#39;s  100  electrical components. In some aspects, each layer  200   a - c  may include etched features on the surface of one or both sides of the respective layer. Although the layers  200   a - c  are shown in  FIG. 1  as positioned against each other, in some aspects, the layers  200   a - c  may include space, insulation, or other material between each layer  200   a - c . Although three layers  200   a - c  are shown, the PCB  200  may include any number of layers, including a single layer PCB, without departing from the scope of the present disclosure. 
       FIG. 2B  also shows components of a multi-antenna device disposed on the layers  200   a - c  of the multi-layer PCB  200 . In this example, the multi-antenna device includes two antennas, a high-frequency antenna  206  and a low-frequency antenna  208 . The high-frequency antenna  206  may be communicatively coupled to a wireless communication device disposed on the PCB  200 . The high-frequency antenna  206  may be tuned for transmitting or receiving radio signals at a frequency range that is higher than, and does not overlap with, the frequency range at which the low-frequency antenna is tuned. In some aspects, the frequency range for the high-frequency antenna  206  may be at least one order of magnitude, or 10 times, greater than the frequency range for the low-frequency antenna. For example, the high-frequency antenna  206  according to some aspects may be tuned for radio frequency signals in a range of 0.5 GHz to 10 GHz. Non-limiting examples of the high-frequency antenna  206  include a Bluetooth antenna, Bluetooth low energy (“BLE”) antenna, Long-Term Evolution (“LTE”), a wireless local access network (“WLAN”) antenna, or other suitable means for transmitting higher-frequency radio signals. For example, the high-frequency antenna  206  of the multi-antenna device may include a Bluetooth or BLE antenna tuned for a frequency of 2.4 GHz. In another example, the high-frequency antenna  206  may include a WLAN antenna tuned for a frequency of 2.4 GHz, 5 GHz, or 5.8 GHz. 
     The low-frequency antenna  208  may be communicatively coupled to a second wireless communication device disposed on the PCB  200 . The low-frequency antenna  208  may be tuned for radio frequency signals in the range of 100 kHz to 100 MHz. Non-limiting examples of the low-frequency antenna  208  include a near-field communication (“NFC”) antenna, a radio-frequency identification (“RFID”) antenna, or other suitable means for transmitting radio signals at lower frequencies. For example, the low-frequency antenna  208  may include a NFC antenna tuned for a frequency of 13.56 MHz. In another example, the low-frequency antenna  208  may include an RFID antenna tuned for a frequency range of 120-150 kHz. In other examples, the low-frequency antenna  208  may include an RFID antenna tuned for a frequency range of 13.56 MHz or 433 MHz. 
     The multi-antenna device also includes a ground plane conductor  210 . The ground plane conductor  210  may include a conductive surface that is connected to a ground terminal of a power supply. The ground plane conductor  210  may be accessible to each of the electrical components on the PCB  200  and may serve as a return path for current from each of the components. In some aspects, the ground plane conductor  210  may include a metal material, such as copper. In additional aspects, the ground plane conductor  210  may also include a ferrite material or other suitable means to reduce the eddy current generated by the metal material during operation of the multi-antenna device at lower frequencies through the low-frequency antenna  208 . The ground plane conductor  210  may have a planar shape and be positioned or disposed on a large surface area of the PCB  200  to allow each of the components access to the circuit board without having to use long traces or component leads. In some aspects, the surface area of the ground plane conductor  210  may cover all or a majority of one of the layers  200   a - c  of the PCB  200 . In some aspects, the high-frequency antenna  206  may be physically and communicatively coupled to the ground plane conductor  210  by a component lead. For example, the high-frequency antenna  206  is connected to the ground plane conductor  210  by lead wire  212 . The lead wire  212  may extend from the high-frequency antenna  206  to the ground plane conductor  210 . 
     To reduce ground plane conductor interference with low-frequency communication (e.g., interference caused by eddy currents), the ground plane conductor  210  may include a contiguous metal surface that defines channels  214  in the ground plane conductor  210 . The channels  214  may be dimensioned to operate as a short circuit during high-frequency wireless communication between the multi-antenna device and an external device, through the high-frequency antenna  206 . For example, the size, shape, or position of the channels  214  may allow them to operate as the short circuit, effectively eliminating the channels  214  during high-frequency transmission. At low-frequencies, the dimensions of the channels  214  may allow the channels  214  to operate as an open circuit during wireless communication between the multi-antenna device and the external device at lower frequencies through the low-frequency antenna. In some aspects, the open-circuit operation may prevent current flow across the ground plane conductor  210  during low-frequency communication to reduce the eddy current caused by the metal material of the ground plane conductor  210 . The desired specification of the channels may correspond to the size, shape, or position of the channels  214  that balances the efficiency in wireless communication for both the high-frequency antenna  206  and the low-frequency antenna  208 . 
     In some aspects, a channel  214  may be defined by a contiguous metal portion of the ground plane conductor  210 . As such, the channels  214  may not extend through the ground plane conductor  210  to entirely physically separate the ground plane conductor  210  into multiple discrete sections. In  FIG. 2B , each channel  214  has a rectangular shape and extends from an edge of the ground plane conductor  210  toward the center  204  of the ground plane conductor  210 . Although four channels  214  are shown in  FIG. 2B , the ground plane conductor  210  may include any number of channels  214 , including only one. Further, while the channels  214  in this example are formed as straight lines extending from the edge of the ground plane conductor  210  towards the center  204 , other arrangements may be employed. For example, one or more channels  214  may be formed extending perpendicularly from the edge of the ground plane conductor  210 , but need not be directed towards the center  204 . For example, multiple channels may be formed extending one edge of the ground plane conductor  210  to create a comb shape. 
     In one aspect, the high-frequency antenna  206  may have a planar shape corresponding to the layer  200   a - c  of the PCB  200  on which the high-frequency antenna  206  is disposed. The high-frequency antenna  206  includes a patterned trace to form a square shape, although other patterns and shapes are possible without departing from the scope of the present disclosure. The high-frequency antenna  206  is communicatively coupled to the ground plane conductor, which may be on the same layer or a different layer of the PCB  200 . In addition, the high-frequency antenna may further be communicatively coupled to a circuit or processor, such as a BlueTooth or WLAN transmitter or receiver, to enable wireless transmission or reception of data using the high-frequency antenna. 
     The low-frequency antenna  208  may be formed along the outer edge of the PCB  200 . In some aspects, the high-frequency antenna  206  may be positioned within a boundary of the low-frequency antenna  208  defined by the perimeter of the low-frequency antenna  208 . In some aspects, the high-frequency antenna  206  and the low-frequency antenna  208  may be positioned on the same layer  200   a - c  of the PCB  200 . In other aspects, the antennas  206 ,  208  may be positioned on separate layers  200   a - c . For purposes of the present disclosure, the boundary of the low-frequency antenna  208  in relation to the position of the high-frequency antenna may refer to a physical boundary created by the perimeter of the low-frequency antenna  208  on the same layer  200   a - c , or may refer to a boundary extending perpendicularly from the physical boundary of the perimeter and through each layer  200   a - c  of the PCB. Further, in some aspects, the high-frequency antenna may be smaller than the low-frequency antenna, and may be positioned within the perimeter of the low-frequency antenna. 
     In some aspects, the low-frequency antenna  208  may also be disposed on the PCB  200 . In other aspects, the low-frequency antenna  208  may be positioned on another surface physically separate from the PCB  200 , such as an internal or external surface of the housing  202 . A lead wire  216  may physically and communicatively couple the low-frequency antenna  208  to the PCB  200  or a component positioned or disposed on the PCB  200 . For example, the low-frequency antenna  208  may be communicatively coupled to a wireless communication device, such as NFC or RFID transmitter or receiver, to enable wireless transmission or reception of data using the low-frequency antenna  208 . In some aspects, the low-frequency antenna  208  may have a planar shape. For example, the low-frequency antenna  208  may be positioned or disposed on a layer  200   a - c  of the PCB  200  and have a planar shape corresponding to the layer. In some aspects, the low-frequency antenna  208  may have a spiral shape. In other aspects, the low-frequency antenna  208  may have a nonplanar shape, such as a coil. The cross-sectional shape of a spiral or coil may be polygonal, such as the rectangular shape of the low-frequency antenna  208  shown in  FIG. 2B , or may be circular. 
       FIG. 3  is a semi-transparent top-down view of another example PCB  200 A for supporting a different configuration of the multi-antenna device according to some aspects of the present disclosure. The PCB  200 A is disposed in a housing  202 A. The PCB  200 A and the housing  202 A have a rectangular shape. The PCB  200 A may incorporate a multi-antenna device having the same high-frequency antenna  206  and low-frequency antenna  208 , but positioned in a different configuration than the PCB  200  and multi-antenna device of  FIGS. 2A and 2B . For example, the high-frequency antenna  206  may be positioned outside the boundary defined by the perimeter of the low-frequency antenna  206 . The low-frequency antenna  208  may be positioned on the same or a different layer of the PCB  200 A than the high-frequency antenna  206 , or may be positioned on an internal or external surface of the housing  202 A. The multi-antenna device may also include a ground plane conductor  300  that is sized to span the length of the PCB  200 A. 
     The ground plane conductor  300  surface defines channels  302 . Similar to the channels  214  of  FIG. 2B , the channels  302  may have dimensions to allow the channels  302  to operate as capacitors providing a short circuit during wireless communication between the multi-antenna device and an external device at higher frequencies through the high-frequency antenna  206 . The dimensions of the channels  302  may also allow the channels  302  to operate as capacitors providing an open circuit during wireless communication between the multi-antenna device and the external device at lower frequencies through the low-frequency antenna  208 . The channels  302  in the ground plane conductor  300  of FIG. may have a rectangular shape and may extend from an edge of the ground plane conductor  300  toward a center of the ground plane conductor  300 . The channels  302  may not intersect with each other to allow the ground plane conductor  300  to include a single, contiguous metal surface. The channels  310  are positioned within the boundary of the perimeter of the low-frequency antenna  208 . In some aspects, the proximity of the channels  310  to the low-frequency antenna  208  may further reduce the eddy current caused by the metal surface of the ground plane conductor  300  when the multi-antenna device is operating at lower frequencies through the low-frequency antenna  208 . 
     The ground plane conductor  300  also defines an additional channel  304 . The additional channel  304  may correspond to the position of the low-frequency antenna  208  overlapping the ground plane conductor  300 . The channel  304  has a rectangular shape and extends across the ground plane conductor  300  in parallel with the ground plane conductor  300 . The channel  304  does not extend the length of the ground plane conductor  300  such that the ground plane conductor  300  remains a contiguous metal surface. The position of the channel  304  allows the low-frequency antenna to overlap only a limited portion of the metal surface of the ground plane conductor  300 , which may reduce the eddy currents produced by the metal portions during operation of the multi-antenna device at lower frequencies through the low-frequency antenna. 
       FIG. 4  is a semi-transparent top-down view of the PCB  200 A including discrete capacitors  400  for an example multi-antenna device. The capacitors  400  are positioned or disposed on the ground plane conductor  300  such that the capacitors  400  span a width of the channels  302 ,  304  to couple the opposing edges of the capacitors  400  to the ground plane conductor  300 . In some aspects, the capacitors  400  may operate as a short circuit when the multi-antenna device is operating in higher frequencies through the high-frequency antenna  206  and may operate as an open circuit when the multi-antenna device is operating in lower frequencies through the low-frequency antenna  208 . Although four capacitors  400  are shown, one for each channel, any number of capacitors  400  may be used. In some aspects, the size of the capacitors  400  may depend on the frequency range of the high-frequency antenna  206  or the frequency range of the low-frequency antenna  208 . In some examples, the capacitors  400  may be sized for a capacitance range between 0.1 pF and 100 pF. 
       FIG. 5  is a semi-transparent top-down view of the PCB  200 A including an alternative ground plane conductor  500  according to some aspects of the present disclosure. The low-frequency and high-frequency antennas may be positioned on the PCB  200 A as described in  FIGS. 3 and 4 . Further, in this example, the ground plane conductor  500  defines channels  502  having different dimensions than the channels  302  of the ground plane conductor  300  shown in  FIG. 3 . The ground plane conductor  500  shown in  FIG. 5  may include a contiguous metal surface defining an interdigital, or crenellated, shape for the channels  502  defined by finger-like projections extending from a surface of the ground plane conductor  500  adjacent to the channels  502 . The crenellated shape of the channels  502  may enhance the capacitance of the channels  502  to operate as a short circuit when the multi-antenna device is operating in higher frequencies through the high-frequency antenna  206  and as an open circuit when the multi-antenna device is operating in lower frequencies through the low-frequency antenna  208 . Further, use of such channels  502  may eliminate the need to incorporate discrete capacitors into the multi-antenna device as the channels  502  may provide the desired capacitance. 
     In this example, the channels  502  extend inward from an outer edge of the ground plane conductor  500 . The channels  502  are defined on the ground plane conductor  500  within the boundary of the low-frequency antenna  208 . Although four channels are shown having the crenellated shape, any number of channels  502  may be used without departing from the scope of the present disclosure. Also, though each channel  502  has a crenellated shape, the channels  502  may have other dimensions, such as a sinusoidal shape or other dimensional means for enhancing the capacitance of the channels  502 . 
       FIG. 6  is a flow chart of a process for manufacturing a multi-antenna device according to aspects of the present disclosure. The process is described with respect to the multi-antenna devices described in  FIGS. 2A-5 , unless otherwise indicated, though other implementations are possible without departing from the scope of the present disclosure. 
     In block  600 , a PCB is provided. The PCB may be a single layer or may be a multi-layer PCB. For example, the PCB may include one of PCB  200  or PCB  200 A. The PCB may include conductive tracks, or other features etched into the surface, to incorporate electrical components (e.g., one or more wireless communication devices) onto to the PCB. 
     In block  602 , a ground plane conductor is formed including contiguous metal surface defining channels in the ground plane conductor. In some aspects, the ground plane conductor may include the ground plane conductor  210  including the channels  214  of  FIG. 2B . In other aspects, the ground plane conductor may include the ground plane conductors  300 ,  500  of  FIGS. 3-5 . For example, the ground plane conductor may include one or more channels having a rectangular shape (e.g., channels  214 ,  302 ) or an interdigital shape (e.g., channels  502 ). The channels may have dimensions to allow the ground plane conductor to operate as a short circuit during wireless communication between the multi-antenna device and an external device at higher frequencies corresponding to the high-frequency antenna  206 . The dimensions of the channels of the ground plane conductor may also allow the ground plane conductor to operate as an open circuit during wireless communication between the multi-antenna device and the external device at lower frequencies corresponding to the low-frequency antenna  208 . 
     In some aspects, the dimensions of the channels may be determined prior to or during the fabrication of the ground metal plane. In one example, prior to fabricating the ground metal plane or disposing it on the PCB provided, simulations or calculations may be performed using known methods to determine a size, shape, and position for the ground metal plane. In some aspects, the desired dimensions or the channel may be determined based on the simulated or calculated efficiency of the high-frequency antenna  206  and the low-frequency antenna  208  provided using the ground metal plane. In some aspects, the desired dimensions of the channels may correspond to the size, shape, or position of the channels that balances the efficiency in wireless communication for both the high-frequency antenna  206  and the low-frequency antenna  208 . 
     In block  604 , the high-frequency antenna  206  and the low-frequency antenna  206  may be formed. The high-frequency antenna  206  may be any radio frequency antenna tuned to a frequency or frequency range that is at least one order of magnitude greater than the frequency or frequency range to which the low-frequency antenna  206  is tuned. For example, the high-frequency antenna may include a Bluetooth antenna tuned to a frequency of 2.4 GHz and the low-frequency antenna may be an NFC antenna tuned to a frequency of 13.56 MHz. In some aspects, the low-frequency antenna  208  may be disposed on the PCB  200 . The low-frequency antenna  208  may be sized to include a perimeter around one or more edges of the PCB. In other aspects, the low-frequency antenna  208  may be disposed on an internal or external surface of the housing (e.g., housing  202  of  FIG. 2 ) and may be coupled to the PCB via a lead wire (e.g., lead wire  216  of  FIG. 2 ). The high-frequency antenna may be disposed on the surface of the PCB. In some aspects, the high-frequency antenna  206  may be positioned within the boundary of the low-frequency antenna  208  as shown in  FIG. 2B . In other aspects, the high-frequency antenna  206  may be positioned external to the boundary of the low-frequency antenna  2  as shown in  FIGS. 3-5 . 
     In block  606 , the high-frequency antenna  206  and the low-frequency antenna  208  may be coupled to the ground plane conductor  210 . In some aspects, the high-frequency antenna  206  and the low-frequency antenna  208  may serve as a communication device for a monitoring device, such as the monitoring device  100  of  FIG. 1 . In some aspects, the ground plane conductor may be positioned on the PCB  200  to allow the channels defined by the ground plane conductor surface to be within a boundary of the perimeter of the low-frequency antenna  208  as shown in  FIGS. 2B-5 . In some aspects, capacitors may be coupled to the ground plane conductor. For example, the capacitors may be positioned over one or more of the channels of the ground plane conductor as shown in  FIG. 4 . 
       FIG. 7  is a flow chart of a process for using a monitoring device including a multi-antenna device according to aspects of the present disclosure. The process is described with respect to the monitoring device  100  of  FIGS. 1A and 1B  and the multi-antenna devices described in  FIGS. 2A-5 , unless otherwise indicated, though other implementations are possible without departing from the scope of the present disclosure. 
     In block  700 , the monitoring device  100  may be attached to a patient&#39;s skin  102 . In some aspects, the monitoring device may be a wearable continuous glucose monitor. The monitoring device  100  may include a housing  202  in which a PCB  200  is disposed including one or more electrical components, such as invasive or non-invasive sensors, for measuring glucose levels of the patient at regular intervals, and a multi-antenna device including the high-frequency antenna  206 , the low-frequency antenna  208 , and a ground plane conductor (e.g., ground plane conductor  210 ,  300 ,  500 ). The ground plane conductor may include channels defined by a contiguous metal surface of the ground plane conductor (e.g., channels  214 ,  302 ,  304 ,  502 ). 
     In some aspects, the monitoring device  100  may be attached to the skin  102  via an adhesive layer on the housing  202  of the monitoring device  100 . In other aspects, the monitoring device  100  may be attached to the skin by injecting an invasive sensor into the subcutaneous tissue of the skin  102 . 
     In block  702 , the external device  104  may be positioned within a coupling range of the monitoring device  100 . In some aspects, the coupling range may be a close range to allow for communication between the monitoring device  100  and the external device  104  in the frequency range corresponding to the low-frequency antenna  208 . For example, the external device  104  may be positioned within 25 cm of the monitoring device  100  (e.g., about 4 cm) to communicatively couple the low-frequency antenna  208  to a compatible antenna type positioned in the external device  104 . In other aspects, the coupling range may be a longer range to allow for communication between the monitoring device  100  in the frequency range corresponding to the high-frequency antenna  206 . For example, the monitoring device  100  may be positioned within 120 m of the external device  104  (e.g., about 100 m) to communicatively couple the high-frequency antenna  206  to a compatible antenna type positioned in the external device  104 . 
     In block  704 , the external device  104  may be used to wirelessly communicate with at least one of the high-frequency antenna  206  or the low-frequency antenna  208  to obtain information from the monitoring device  100 . For example, the monitoring device  100  may wirelessly transmit measurements recorded by sensors coupled to the PCB in the frequency range corresponding to the high-frequency antenna  206  or the low-frequency antenna  208  depending, at least in part, on the proximity of the monitoring device  100  to the external device  104 . The channels of the ground plane conductor coupled to the PCB may operate as a short circuit during a transmission by the multi-antenna device in the frequency range corresponding to the high-frequency antenna  206  and as an open circuit during a transmission by the multi-antenna device in the frequency range corresponding to the low-frequency antenna  208 . 
     As discussed above, one or more suitable devices according to this disclosure may include a processor or processors. The processor may be in communication with a computer-readable medium, such as a random access memory (RAM) coupled to the processor. The processor executes computer-executable program instructions stored in memory. Such processors may comprise a microprocessor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), field programmable gate arrays (FPGAs), and state machines. Such processors may further comprise programmable electronic devices such as PLCs, programmable interrupt controllers (PICs), programmable logic devices (PLDs), programmable read-only memories (PROMs), electronically programmable read-only memories (EPROMs or EEPROMs), or other similar devices. 
     Such processors may comprise, or may be in communication with, media, for example computer-readable storage media, that may store instructions that, when executed by the processor, can cause the processor to perform the steps described herein as carried out, or assisted, by a processor. Examples of computer-readable media may include, but are not limited to, an electronic, optical, magnetic, or other storage device capable of providing a processor with computer-readable instructions. Other examples of media comprise, but are not limited to memory chips, ROM, RAM, ASICs, configured processors, or any other medium from which a computer processor can read. The processor, and the processing, described may be in one or more structures, and may be dispersed through one or more structures. The processor may comprise code for carrying out parts of one or more of the methods (or parts of methods) described herein. 
     The foregoing description of the examples, including illustrated examples, of the invention has been presented only for the purpose of illustration and description and is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Numerous modifications, adaptations, and uses thereof will be apparent to those skilled in the art without departing from the scope of this invention. The illustrative examples described above are given to introduce the reader to the general subject matter discussed here and are not intended to limit the scope of the disclosed concepts. 
     Reference herein to an example or implementation means that a particular feature, structure, operation, or other characteristic described in connection with the example may be included in at least one implementation of the disclosure. The disclosure is not restricted to the particular examples or implementations described as such. The appearance of the phrases “in one example,” “in an example,” “in one implementation,” or “in an implementation,” or variations of the same in various places in the specification does not necessarily refer to the same example or implementation. Any particular feature, structure, operation, or other characteristic described in this specification in relation to one example or implementation may be combined with other features, structures, operations, or other characteristics described in respect of any other example or implementation. 
     Use herein of the word “or” is intended to cover inclusive and exclusive OR conditions. In other words, A or B or C includes any or all of the following alternative combinations as appropriate for a particular usage: A alone; B alone; C alone; A and B only; A and C only; B and C only; and A and B and C.