The present disclosure relates to the field of electronics technologies, and in particular to a circularly polarized antenna structure and a wearable device.
Wearable devices are becoming more and more popular among users due to diverse functions thereof. These functions may be implemented by means of built-in antenna structures of the wearable devices.
Taking a satellite positioning antenna as an example, with the development of the wearable devices, a satellite positioning function has become one of the essential functions. Commonly used satellite positioning systems generally include Global Positioning System (GPS), BeiDou Navigation Satellite System (BDS), and Global Navigation Satellite System (GLONASS).
In order to enhance a transmission efficiency from the satellite to the ground, e.g., to enhance a penetration capacity, a coverage area or the like, a transmitting antenna of the satellite to the ground can be circularly polarized. Likewise, in order to enhance a reception capability of a positioning antenna, a receiving antenna of a device may adopt a circularly polarized antenna similar to the transmitting antenna. However, it can be difficult to adopt circularly polarized antennas in the wearable devices due to the limitation of volume or industrial design, and linearly polarized antennas are generally adopted, which lead to poor satellite positioning performance and inaccurate capture of motion trajectories.
Implementations of the present disclosure provide a circularly polarized antenna structure and a wearable device.
In a first aspect, an implementation of the present disclosure provides a circularly polarized antenna structure, applicable to a wearable device, the antenna structure including a mainboard; an annular radiator, having an effective perimeter equal to a wavelength corresponding to a central operating frequency of the antenna structure; a feeding terminal electrically connected to the radiator at one end and connected to a feeding module of the mainboard at the other end; and a grounding terminal electrically connected to the radiator at one end and electrically connected to a grounding module of the mainboard through a first capacitor at the other end.
In some implementations, a line connected between the feeding terminal and a center point of the radiator is a first connecting line, and a line connected between the grounding terminal and the center point of the radiator is a second connecting line, and a first included angle β is formed from the first connecting line to the second connecting line along a first direction; the first direction is a counterclockwise direction around the radiator; and
.
In some implementations, the first included angle β is 10° to 80°.
In some implementations, the radiator has an annular structure in one of shapes including: a circular ring, an elliptical ring, a rectangular ring, a triangular ring, a diamond ring, or a polygonal ring.
In some implementations, the antenna structure includes one of: a satellite positioning antenna, a Bluetooth antenna, a WiFi antenna, or a 4G/5G antenna.
In some implementations, the first capacitor has a capacitance value of 0.2 pF to 1.5 pF.
In some implementations, the first included angle β is 25°, and the capacitance value of the first capacitor is 0.5 pF.
In a second aspect, an implementation of the present disclosure provides a wearable device, including the circularly polarized antenna structure according to any one of implementations in the first aspect.
In some implementations, the wearable device includes a smart watch, the smart watch including: a case in which the mainboard is disposed; and a metal bezel surrounding an edge of an open end of the case and forming the radiator.
In some implementations, the smart watch further includes a screen assembly assembled to the open end of the case through the metal bezel.
In some implementations, the wearable device includes one of: a smart bracelet, a smart watch, smart earphones, or smart glasses.
In order to explain detailed description of the present disclosure or technical solutions in the related art more clearly, the drawings to be used in the detailed description or description of the related art will be briefly introduced below. It is apparent that the drawings in the following description illustrate some implementations of the present disclosure. For those ordinary skilled in the art, other drawings may be obtained from these drawings without any creative efforts.
Implementations of the present disclosure will be clearly and completely described below with reference to the accompanying drawings. It is apparent that the described implementations are part of the implementations of the present disclosure, rather than all of the implementations. All other implementations obtained by those ordinary skilled in the art based on the implementations of the present disclosure without any creative efforts shall fall within the protection scope of the present disclosure. In addition, technical features involved in different implementations of the present disclosure described below may be combined with each other as long as they do not conflict with each other.
Circularly polarized antennas are more commonly applied in satellite navigation systems. This is due to the fact that circularly polarized waves generated by the circularly polarized antennas may be received by linearly polarized antennas in any direction, while the circularly polarized antennas may receive incoming waves from the linearly polarized antennas in any direction, resulting in a good antenna performance. Therefore, the circularly polarized antennas are commonly used in satellite positioning, reconnaissance and jamming. The circularly polarized antennas may be divided into left-hand circularly polarized (LHCP) antennas and right-hand circularly polarized (RHCP) antennas. Taking satellite positioning antennas as an example, the major global satellite navigation and positioning systems include GPS, BeiDou, GLONASS, and Galileo, and the satellite positioning antennas in these systems have all adopted the right-hand circularly polarized antennas.
With the development of wearable devices, a satellite positioning function has become one of the essential functions. Taking smart watches as an example, the satellite positioning function may be used in various application scenarios such as motion assistance, trajectory detection, and positioning. However, it can be difficult for the wearable devices to adopt the circularly polarized antennas due to the limitation of volume or industrial design. Most of the satellite positioning antennas in the wearable devices on the market are implemented using the linearly polarized antennas, such as IFAs (Inverted-F Antennas), and slot antennas. However, the linearly polarized antennas have lower efficiency in receiving the circularly polarized waves transmitted from the satellite, which leads to poor positioning accuracy and trajectory detection performance of the wearable devices, making them difficult to meet requirements for high-accuracy positioning.
In order to solve the above problems, some smart watches have started to use the circularly polarized antennas as the satellite positioning antennas. In particular, a circularly polarized antenna performance is generated by feeding an inverted-F antenna (IFA) under a metal ring on an upper surface of the watch, and coupling another parasitic antenna unit (i.e., a grounding branch of the IFA) with the metal ring of the watch. In this circularly polarized design, there are special requirements for lengths of the IFA antenna and the parasitic antenna unit in order to produce a circulating current in the metal ring. That is, the length of the IFA and/or the parasitic antenna unit may be approximately one-quarter arc length of the metal ring so as to achieve an effect of “pulling” the current in the metal ring to produce an effective circulating current. The “effective circulating current” referred to herein means that the produced circulating current may be circulated more uniformly along the metal ring as the phase changes, so as to realize the current of the circularly polarized antenna. In this scheme, because the circulating current in the metal ring is realized by the coupling among the IFA antenna, the parasitic antenna unit, and the metal ring of the watch, there are higher design requirements for coupling gaps among the IFA antenna, the parasitic antenna unit, and the metal ring, which increases the difficulty in antenna design. Furthermore, in this scheme, the IFA antenna and the parasitic antenna unit are FPC (Flexible Printed Circuit) antennas or LDS (Laser Direct Structuring) antennas placed on an antenna bracket, and the antenna bracket undoubtedly occupies the limited space in the watch, which makes application of this scheme for the wearable devices with limited volumes.
In view of the above, implementations of the present disclosure provide a circularly polarized antenna structure with a simple and effective structure, and the antenna structure is applicable to a wearable device, enabling the device to implement an antenna in a circularly polarized form. It may be understood that the wearable device described in the following implementations of the present disclosure may be in any form suitable for implementation, for example, a watch-type device such as a smart watch or a smart bracelet; a glass-type device such as smart glasses, VR glasses, or AR glasses; or a wearable device such as smart clothing or wearing accessories, which is not limited in the present disclosure.
As shown in
The feeding terminal 110 may be connected across the gap formed between the mainboard 100 and the radiator 200. That is, one end of the feeding terminal 110 is electrically connected to the radiator 200, and the other end is connected to the feeding module of the mainboard 100. It may be understood that the feeding terminal 110 and the radiator 200 may be separately formed or may be integrally formed, which is not limited in the present disclosure. In an example, the feeding terminal 110 is integrally formed with the radiator 200, and a free end of the feeding terminal 110 is electrically connected to the feeding module of the mainboard 100 through an elastic member on the mainboard 100, where the feeding terminal 110 is connected to the mainboard 100 to form the feeding point 111.
The grounding terminal 120 may also be connected across the gap formed between the mainboard 100 and the radiator 200; that is, one end of the grounding terminal 120 is electrically connected to the radiator 200, and the other end is connected to the grounding module of the mainboard 100. It may be understood that the grounding terminal 120 and the radiator 200 may be separately formed or may be integrally formed, which is not limited in the present disclosure.
With continued reference to
For the circularly polarized antenna structure with the annular radiator, an effective perimeter of the radiator is equal to a wavelength corresponding to a central operating frequency of the antenna structure. Therefore, in case of implementing an antenna structure with a different frequency, it is necessary to set the effective perimeter of the radiator equal to the wavelength corresponding to that different frequency.
It should be noted that, in free space, a physical perimeter around the radiator 200 is the effective perimeter of the radiator 200. However, in an assembled state, assembly structures and materials around the radiator 200 may increase the effective perimeter of the radiator 200; that is, a resonance frequency of the radiator 200 is reduced. For example, when the radiator 200 is assembled with a plastic material (e.g., a plastic bracket or a nano-molded material), the material may increase the effective perimeter of the radiator. Meanwhile, a screen assembly near the radiator 200 such as a glass cover of the screen assembly may have an effect of increasing the effective perimeter of the radiator.
The effective perimeter of the radiator 200 is increased because dielectric constants of both the plastic material and the glass cover are greater than that of air, where the dielectric constant of the plastic and the nano-molded materials is typically 2-3, and the dielectric constant of the glass cover is typically 6-8, and the introduction of materials with high dielectric constants may increase a current intensity in the vicinity of the radiator 200, which in turn increases the effective perimeter of the radiator 200. That is, the actual physical perimeter of the radiator 200 may be reduced in condition of achieving a same resonance frequency by the radiator 200. Therefore, those skilled in the art may understand that the term “effective perimeter” in the implementations of the present disclosure refers to an effective electrical length of the radiator during the actual production of the resonant electric waves, and is not limited to being interpreted as a physical length.
At least one inventive concept of the antenna structure in the present disclosure is to produce a circularly polarized wave by directly feeding the annular radiator 200 and pulling the current generated by the radiator 200 with the grounded first capacitor 121 to form a circulating current being rotated. The principle of production and performance exploration of the circularly polarized wave will be described in detail below, and will not be detailed herein.
As can be seen from the above, implementations of the present disclosure provide a circularly polarized antenna structure, which is applicable to a wearable device. The antenna structure includes a mainboard and an annular radiator, and an effective perimeter of the radiator is equal to a wavelength corresponding to a central operating frequency of the antenna structure. A feeding terminal and a grounding terminal are connected between the mainboard and the radiator. One end of the feeding terminal is electrically connected to the radiator, and the other end of the feeding terminal is connected to a feeding module of the mainboard. One end of the grounding terminal is electrically connected to the radiator, and the other end of the grounding terminal is electrically connected to a grounding module of the mainboard through the first capacitor. The current in the radiator is pulled by the first capacitor, such that the annular radiator produces an effective circulating current being rotated, thereby forming a circularly polarized wave and realizing the circularly polarized antenna structure. Compared with a linearly polarized antenna structure, the circularly polarized antenna structure has higher reception efficiency, resulting in more accurate positioning in implementing a satellite positioning function. By directly feeding the annular radiator without providing other coupling antenna structures, structure and cost of the circularly polarized antenna may be greatly simplified, making it easier to be implemented in wearable devices with small volume and space such as smart watches.
The implementation and principle of the antenna structure in the present disclosure will be described in detail below with reference to a specific implementation shown in
As shown in
As shown in
The implementation of the circularly polarized antenna in this implementation will be described below based on the structure shown in
First, the circularly polarized antenna may be implemented in two ways. In the first way, the circulating current, which is produced in case of the effective perimeter of the radiator being an integer multiple of the wavelength corresponding to the operating frequency, may form circular polarization. In the second way, two linear currents, which are mutually quadrature and have equal amplitudes and a phase difference of 90°, may form circular polarization. The circularly polarized antenna in this implementation is implemented in the first way. In this implementation, taking a GPS signal with a central operating frequency of 1.575 GHz as an example, a wavelength of the GPS signal may be calculated from the central operating frequency, and the actual physical perimeter of the metal bezel in case of the effective wavelength may be designed based on the influence of the components of the watch such as the case and/or the screen on the wavelength.
For the metal bezel with the effective perimeter equal to one wavelength of the GPS signal, in the implementation of the present disclosure, a rotating current field that rotates in a single direction is formed inside the metal bezel by directly feeding the metal bezel and effectively pulling the generated current using the first capacitor 121.
As shown in
The antenna performance and influencing factors of the circularly polarized antenna in this implementation will be further described below. For illustration purposes, a display screen of the watch is defined as the xy plane, and a direction perpendicular to the display screen of the watch and pointing to the sky is the +z direction, such that a rectangular coordinate system of xyz space may be established. Furthermore, as shown in
As shown in
in which the current reaches a peak value at 90° from a zero value at 0°;
in which the current drops to a zero value at 180° from the peak value at 90°.
in which the current reaches a peak value at 270° from the zero value at 180°; and
in which the current drops to a zero value at 360° from the peak value at 270°.
The above current distribution is a periodic current change distribution, which may periodically rotate in the annular metal bezel over time under the effect of the first capacitor 121, such that the circularly polarized wave as described above is formed. Moreover, if the current is rotated in a clockwise direction in the metal bezel, a left-hand circularly polarized wave is produced, and if the current is rotated in a counterclockwise direction in the metal bezel, a right-hand circularly polarized wave is produced.
Further, since the current in the metal bezel is rotated under the effect of the first capacitor 121, if the first included angle β satisfies
he current is “pulled” to rotate counterclockwise; on the other hand, if the first included angle β satisfies
the current is “pulled” to rotate clockwise. This is due to that the phase of the current across the first capacitor 121 is 90° ahead of the phase of the voltage across the first capacitor 121 in an AC circuit. Therefore, when the first included angle β satisfies
the phase of the current across the first capacitor 121 being 90° ahead may cause the current in the annular radiator 200 to rotate in the counterclockwise direction, thereby realizing a right-hand circularly polarized antenna. Similarly, when the first included angle β satisfies
the phase of the current across the first capacitor 121 being 90° ahead may cause the current in the annular radiator 200 to rotate in the clockwise direction, thereby realizing a left-hand circularly polarized antenna.
Meanwhile, combined with the characteristic that, in the presence of the circularly polarized wave in the annular radiator, the circulating current producing the circularly polarized wave has a periodic distribution on the entire circumference of the annular radiator, it can be known that the circularly polarized antenna satisfies the following rules: if the first included angle β satisfies
the current rotates counterclockwise to produce a right-hand circularly polarized wave; while if the first included angle β satisfies
the current rotates clockwise to produce a left-hand circularly polarized wave, where “U” denotes a union of two sets.
At this point, considering that the satellite positioning antennas use the right-hand circularly polarized antennas, the antenna structure, when used as the satellite positioning antenna, may form the right-hand circularly polarized antenna. Therefore, when the antenna structure is used as the satellite positioning antenna, the first included angle β preferably satisfies
However, it may be understood by those skilled in the art that in other implementations, the first included angle β may be set to
thereby forming the left-hand circularly polarized antenna.
As can be seen from the above, with the circularly polarized antenna structure according to the implementations of the present disclosure, the line connected between the feeding terminal and the center point of the radiator is the first connecting line, the line connected between the grounding terminal and the center point of the radiator is the second connecting line, and the included angle from the first connecting line to the second connecting line along the counterclockwise direction is the first included angle. By adjusting the first included angle, that is, changing the position of the first capacitor, circularly polarized antennas with different directions may be realized. If the first included angle is in a range from 0° to 90° or in a range from 180° to 270°, the current in the radiator rotates counterclockwise to form the right-hand circularly polarized antenna; and if the first included angle is in a range from 90° to 180° or in a range from 270° to 360°, the current in the radiator rotates clockwise to form the left-hand circularly polarized antenna. With the antenna structure in the present disclosure, circularly polarized waves with different directions may be realized by adjusting the first included angle, which can meet design requirements for the circularly polarized antennas with different directions.
As can be seen from the foregoing, a circularly polarized wave may be decomposed into two linearly polarized waves mutually quadrature with equal amplitudes and a phase difference of 90°. Meanwhile, according to the current distribution of the resonant wave, the current zero point of an electric wave of one order corresponds to the current peak point of an electric wave of another order. Therefore, in order to improve the effect of the first capacitor 121 on the circular polarization, the position of the first capacitor 121 may be as far away as possible from the positions where the current is zero, that is, the positions where the first included angle β is 0°, 90°, 180°, and 270°.
In addition, since the satellite positioning antenna in this implementation considers only right-hand circular polarization, and also considering that there are many other components in the smart watch, such as FPCs for heart rate and the screen, side buttons of the watch, and speakers, the feeding terminal 110 and the grounding terminal 120 may be disposed as close as possible, so as to avoid the influence of the aforementioned components located between the feeding point and the grounding point on the antenna performance. Therefore, in an implementation, the first included angle β is preferably in a range from 10° to 80°.
With the circularly polarized antenna structure according to the implementations of the present disclosure, the first included angle ranges from 0° to 90° to form a right-hand circularly polarized wave. Since a transmitting antenna for satellite positioning uses the right-hand circularly polarized wave, using a right-hand circularly polarized antenna structure for reception can improve the antenna efficiency and positioning accuracy. The first included angle is further preferably in the range from 10° to 80°, such that the position of the first capacitor is far away from the current zero positions (i.e., the positions where the first included angle β is 0°) or the current peak positions (i.e., the positions where the first included angle β is 90°) of two quadrature components of the circularly polarized wave, so as to maintain the independence of the two quadrature components of the wave, thus improving the radiation efficiency of the circularly polarized antenna and improving the antenna performance.
After determining the first included angle β as in the range from 10° to 80° as described above, the antenna structure may be further optimized below.
Axial ratio (AR) is an important parameter to characterize the performance of the circularly polarized antenna. AR refers to a ratio of two quadrature electric field components of the circularly polarized wave. The smaller the AR, the better the circular polarization performance; and on the contrary, the larger the AR, the worse the circular polarization performance. In the application scenario of this implementation, an indicator of the performance of the circularly polarized antenna is that the AR should be less than 3 dB.
On the other hand, since an important characteristic of the circularly polarized antenna in this implementation is to use the first capacitor to pull the current in the metal bezel. The pulling effects achieved by capacitors with different capacitance values are different. Through a large number of comparative experimental studies, the capacitance value of the first capacitor, the first included angle β, and the operating frequency with the axial ratio less than 3 dB satisfy the following relationships:
If the capacitance value of the first capacitor remains fixed, the operating frequency with the axial ratio less than 3 dB decreases as the first included angle β increases. If the first included angle β remains fixed, the operating frequency with the axial ratio less than 3 dB decreases as the capacitance value increases. In addition, when the first included angle β is less than 45°, the operating frequency with the axial ratio less than 3 dB has a smaller trend of change with the capacitance value of the first capacitor; on the contrary, when the first included angle β is greater than 45°, the operating frequency with the axial ratio less than 3 dB has a larger trend of change with the capacitance value of the first capacitor. Moreover, the first capacitor with a relatively large capacitance value may be provided when the first included angle β is less than 45°; on the contrary, the first capacitor with a relatively small capacitance value may be provided when the first included angle β is greater than 45°. The capacitance value (in the unit of pF) of the first capacitor may be in the range from 0.2 pF to 1.5 pF.
Based on the above characteristic, the circularly polarized antenna may be optimized by adjusting the first included angle β and the capacitance value of the first capacitor. The optimization goal is that the operating frequency range of the antenna meets the frequency requirement of the satellite positioning antenna, while the axial ratio in the frequency range is less than 3 dB.
In an example, the optimization requirement is met in case of the first included angle β being 25° and the capacitance value of the first capacitor being 0.5 pF. In this case, a satellite positioning antenna with right-hand circular polarization and an axial ratio less than 3 dB in the operating frequency range may be realized.
In order to further illustrate the performance of the antenna in this example, a GPS satellite positioning antenna with a central operating frequency of 1.575 GHz is used as an example below to further describe the performance of the antenna.
The structure and principle of the circularly polarized antenna structure according to the implementations of the present disclosure have been described in detail above, and there may be other alternative implementations of the present disclosure suitable for implementation based on the above implementations.
In some alternative implementations, the radiator of the smart watch described above is not limited to being implemented by the metal bezel, but may be implemented by the metal frame or other part of the case such as a metal middle frame. For example, in the implementation shown in
In other implementations, the antenna structure according to the present disclosure is not limited to being applicable to the smart watch, but may be applicable to any other wearable devices suitable for implementation, such as smart bracelets or smart earphones, which is not limited in the present disclosure. Meanwhile, it may be understood that when the antenna structure is applied to other forms of wearable devices, the radiator may be implemented by other structures accordingly. Also, an annular structure of the radiator may not be limited to a circular ring, but may be implemented by any other form of ring. For example, in some examples, the annular structure of the radiator may have one of shapes including an elliptical ring, a rectangular ring, a rounded rectangular ring, a diamond ring, a triangular ring, or other polygonal ring, which is not limited in the present disclosure.
In yet other alternative implementations, the antenna structure according to the present disclosure is not limited to implementing a satellite positioning antenna, but may implement any other type of antenna suitable for implementation, such as a Bluetooth antenna, a WiFi antenna, or a 4G/5G antenna. The antenna structure according to the present disclosure may be used to implement any type of circularly polarized antenna where the size and space of the device allow, which is not limited in the present disclosure.
As can be seen from the above, with the circularly polarized antenna structure according to the implementations of the present disclosure, a circularly polarized antenna may be implemented in a wearable device, thereby improving the antenna reception efficiency and antenna performance of the wearable device and improving the positioning accuracy. Moreover, the structure for realizing the circularly polarized antenna is simple without coupling other structures, which greatly simplifies the structure and cost of the circularly polarized antenna, making it easier to be implemented in a wearable device with a smaller volume. Furthermore, the antenna structure according to the implementations of the present disclosure has a better circular polarization performance, which can further improve the positioning accuracy.
In a second aspect, an implementation of the present disclosure provides a wearable device, including the circularly polarized antenna structure according to any one of the above implementations, such that a circularly polarized antenna may be implemented in the wearable device to improve the antenna performance of the wearable device.
The wearable device may include any wearable device suitable for implementation, such as a smart watch, a smart bracelet, smart earphones, or smart glasses, which is not limited in the present disclosure.
In an example, the wearable device is a smart watch, and the structure of the smart watch may be implemented with reference to the above implementations in
As can be seen from the above, the wearable device according to the implementations of the present disclosure includes the circularly polarized antenna structure, such that a circularly polarized antenna may be implemented in the wearable device to improve the antenna reception efficiency and antenna performance of the wearable device and improve the positioning accuracy. Moreover, the structure for realizing the circularly polarized antenna is simple without coupling other structures, which greatly simplifies the structure and cost of the circularly polarized antenna, making it easier to be implemented in a wearable device with a smaller volume. Furthermore, the wearable device according to the implementations of the present disclosure has a better circularly polarized antenna performance, which can further improve the positioning accuracy. In addition, when the wearable device is a smart watch, the radiator may be formed by using the bezel and/or frame of the smart watch. On the one hand, the bezel and/or frame can be used as a decorative structure for the watch to improve the aesthetics of the device; on the other hand, using the bezel and/or frame as the radiator can reduce the occupation of the internal space of the watch by the antenna structure and effectively increase the volume of the radiator, thereby greatly enhancing the radiation performance of the antenna.
It is apparent that the above implementations are merely examples for clarity of illustration, and are not limitations on the implementations. For those ordinary skilled in the art, other variations or modifications in different forms may be made based on the above description. It is not necessary or possible to exhaust all implementations herein. However, obvious variations or modifications derived therefrom still fall within the protection scope of the present disclosure.
Number | Date | Country | Kind |
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202010833927.9 | Aug 2020 | CN | national |
202021727353.9 | Aug 2020 | CN | national |
The present application is a continuation of PCT/CN2021/112445, filed Aug. 13, 2021, which claims priority and benefit of Chinese Patent Application Nos. 202021727353.9 and 202010833927.9, both filed Aug. 18, 2020, the entire disclosures of all of which are hereby incorporated by reference.
Number | Date | Country | |
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Parent | PCT/CN2021/012445 | Aug 2021 | WO |
Child | 18162477 | US |