Circularly polarized antenna and wearable device

Abstract

The application discloses a circularly polarized antenna and a wearable device, and forms a first slot antenna between a first ground structure and a second ground structure and forms a second slot antenna between the second ground structure and a third ground structure, the electric field amplitudes of the first slot antenna and the second slot antenna are equal, there is a magnetic coupling effect between the two slot antennas, the orthogonal electric field components of the two slot antennas form a phase difference of 90 degrees, a pair of spatially orthogonal slot antennas are constructed, a pair of orthogonal equal-amplitude electric field components are generated, and the circular polarization effect of the antenna is realized. Furthermore, the first slot antenna is connected with a first lumped element matching network, and the second slot antenna is connected with a second lumped element matching network, so that the resonant mode of the two slot antennas is changed from 1 / 2 wavelength resonance to 1 / 4 wavelength resonance, thereby realizing the miniaturization effect of the antenna. The antenna with the above-mentioned circular polarization and miniaturization characteristics is particularly suitable for miniaturized wearable devices such as smart watches.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of antennas, and particularly relates to a circularly polarized antenna and a wearable device having the same. BACKGROUND

[0002] In recent years, with the rapid development of the communication technology field, electronic terminal devices such as mobile phones, tablet computers and smart watches have been popularized on a large scale, and more and more terminal devices adopt metal shells or metal frames to improve the appearance and texture of the products. In order to realize precise positioning and other functions, antennas are integrated in electronic terminal devices, but the structure of the metal shell or metal frame often restricts the performance of the antenna, in addition, with the requirement of thinness of the electronic terminal device, the design space of the antenna is becoming smaller and smaller. On the other hand, in order to better receive navigation satellite signals, the positioning antenna of the smart electronic terminal device needs to be designed to right-hand circularly polarized radiation, through the above design, the polarization mismatch and the Faraday rotation effect of the ionosphere can be overcome, and the left-hand polarized navigation satellite positioning signal reflected by high-rise buildings or the ground can be filtered, thereby reducing the multipath interference and effectively improving the positioning accuracy of the electronic terminal device.

[0003] For wearable devices such as smart watches, it is extremely challenging to design a terminal antenna in a circularly polarized form in the case of a small size metal frame, because: (1) the length of the gap formed by the metal frame is too short, and the resonant frequency is too high. For the 1.575GHz frequency point of satellite positioning, the resonant frequency of the smart watch frame gap is 2-3 times the frequency of 1.575GHz; (2) it is difficult to meet the requirement of circular polarization of the antenna, that is, it is difficult to realize a pair of equal-amplitude orthogonal linear polarization modes resonating at 1.575GHz frequency point, and the phase difference is 90°. Therefore, at present, there is no circularly polarized antenna that can meet the small size metal frame gap in the prior art to be applied to wearable devices such as smart watches.

[0004] Currently, common terminal antennas mainly include linear polarization and circular polarization, and the linear polarization includes monopole antenna, inverted L antenna (ILA), inverted F antenna (IFA), planar inverted F antenna (PIFA), loop antenna and slot antenna; the circular polarization includes floor radiation antenna and antenna based on coupling structure. For linear polarization antennas, the document Heptaband Inverted-F Antenna With Independent Resonance Control for Mobile Handset Applications (IEEE Antennas and Wireless Propagation Letters, vol. 13, pp. 1267-1270, 2014, J. Lee, and Y. Sung) reports an IFA antenna covering multiple frequency bands, which can be regarded as a curved single-pole antenna with a ground short-circuit branch, and has the advantages of low profile and easy impedance matching adjustment. The document A Reconfigurable Antenna for Quad-Band Mobile Handset Applications (IEEE Transactions on Antennas and Propagation, vol. 60, no. 6, pp. 3003-3006, Jun, 2012, Y. K. Park, and Y. Sung) reports a reconfigurable multi-band PIFA antenna, which can cover the frequency bands of 880-960MHz and 1710-2170Mhz. By loading a slot on the PIFA antenna, the current path is lengthened, and the effect of antenna miniaturization is achieved; by adjusting the short-circuit point, the feed point position and the shape of the slot, additional resonant modes can be introduced to realize dual / multi-band design. Meanwhile, compared with IFA antenna, PIFA antenna also has higher bandwidth. The document A Compact and Low-Profile Loop Antenna With Six Resonant Modes for LTE Smartphone (IEEE Transactions on Antennas and Propagation, vol. 64, no. 9, pp. 3743-3751, Sep, 2016, Xu, H. Y. Wang, S. Gao et al) designs a low-profile loop antenna with six resonant modes. The loop antenna has the characteristics of multi-resonant modes, such as λ / 2, 3λ / 4 and λ resonant modes, which can meet the demand of terminal device antenna multi-band coverage.The document “Hepta-Band Metal-Frame Antenna for LTE / WWAN Full-Screen Smartphone, IEEE Antennas and Wireless Propagation Letters, vol. 19, no. 7, pp. 1241-1245, Jul, 2020, Y. Liu, W. Cui, Y. T. Jia et al” reports a kind of mobile terminal antenna for LTE system based on uninterrupted metal frame, which realizes wideband and multi-frequency design by adjusting the length, position and feed structure of the slot. Although the above linearly polarized antennas have their own advantages, they are difficult to be applied to receive circularly polarized signals, and polarization mismatch, multipath effect, channel crosstalk and other problems are prone to occur.

[0005] For circularly polarized antennas, the document “Circular Polarized Ground Radiation Antenna for Mobile Applications” (IEEE Transactions on Antennas and Propagation, vol. 66, no. 5, pp. 2655-2660, May, 2018, L. Qu, Z. Zahid, H. H. Kim et al) reports a single-feed circularly polarized floor radiation antenna applied to mobile intelligent devices, which is composed of a square floor and two miniaturized antennas as exciters. Both antennas are loaded with LC lumped elements to adjust the resonant frequency of a pair of orthogonal modes of the floor, so as to obtain a circularly polarized radiation with edge radiation. The document “A Novel PIFA Antenna For Broad Band Circular Polarization” (Microwave and Optical Technology Letters, vol. 53, no. 1, pp. 204-208, Jan, 2011, L. H. Wen, Y. Z. Yin, Y. Wang et al) reports an antenna composed of a PIFA antenna and a square floor, with arrow-shaped branches at the corners of the floor as a coupled broadband circularly polarized antenna. This antenna can be applied to intelligent terminal devices without metal frames, but when the terminal device is wrapped in a metal frame, the antenna will be strongly affected by coupling, resulting in a significant decline in antenna performance.

[0006] Therefore, according to the characteristics of small-size metal frame, a kind of antenna with circular polarization characteristics is designed, which is the current technical problem to be solved for wearable intelligent terminal devices. SUMMARY

[0007] To this end, the technical problem to be solved by the present application is that the existing antenna is difficult to meet the wearable smart terminal device with small size and metal frame, so that a circularly polarized antenna and wearable device are provided, which can meet the circular polarization performance requirement of the metal frame terminal device and has high radiation efficiency.

[0008] To solve the above technical problems, the technical solution of the present application is:

[0009] The present application provides a circularly polarized antenna in the first aspect, which comprises:

[0010] A metal frame;

[0011] A circuit board is arranged inside the metal frame and is arranged in a spaced manner with the metal frame, and a gap is formed between the circuit board and the metal frame;

[0012] A first ground structure is arranged in the gap and is electrically connected with the metal frame;

[0013] A second ground structure is arranged in the gap and is arranged in a spaced manner with the first ground structure, and the second ground structure is electrically connected with the metal frame, and a first gap antenna is formed between the second ground structure and the first ground structure;

[0014] A third ground structure is arranged in the gap and is arranged in a spaced manner with the first ground structure and the second ground structure, and the third ground structure is electrically connected with the metal frame, and a second gap antenna is formed between the third ground structure and the second ground structure, and the electric field amplitudes of the first gap antenna and the second gap antenna are equal and the phase difference is 90°;

[0015] The first gap antenna is connected with a first lumped element matching network, and the second gap antenna is connected with a second lumped element matching network.

[0016] As a preferred, a fourth ground structure is further included, the circuit board is connected with a feeding port, the fourth ground structure is connected with the first lumped element matching network and the feeding port, and the first lumped element matching network is further connected to the metal frame.

[0017] As a preferred, a fifth ground structure is further included, the fifth structure is connected to the second lumped element matching network, and the second lumped element matching network is further connected to the metal frame.

[0018] As a preferred, the first gap antenna and the second gap antenna have an included angle of 75-105°.

[0019] As a preferred, the first lumped element matching network is an L-shaped matching network, and the first lumped element matching network is loaded with a first lumped element and a second lumped element.

[0020] As preferred, the second lumped element matching network is an L-shaped matching network, and the first lumped element matching network is loaded with a third lumped element and a fourth lumped element.

[0021] As preferred, the first, second, third and fourth lumped elements are capacitors or inductors.

[0022] As preferred, the metal frame is a rectangular frame, the circuit board is a rectangular board, and a rectangular gap is formed between the metal frame and the circuit board; the first ground structure is arranged at a first corner of the rectangular gap, the second ground structure is arranged at a second corner of the rectangular gap, the first corner and the second corner are arranged adjacent to each other along a short side of the rectangular gap, and the third ground structure is arranged adjacent to a third corner of the rectangular gap, the third corner and the second corner being arranged adjacent to each other along a long side of the rectangular gap.

[0023] As preferred, the fourth ground structure is further electrically connected with a first microstrip feed line, and the fourth ground structure is connected to the feed port through the first microstrip feed line; and the fifth ground structure is connected with a second microstrip feed line.

[0024] The second aspect of the present application provides a wearable device comprising the circularly polarized antenna.

[0025] The above technical solution of the present application has the following advantages compared with the prior art:

[0026] The circularly polarized antenna provided by the present application has the following advantages: the first ground structure, the second ground structure and the third ground structure are arranged in the gap between the metal frame and the circuit board, a first slot antenna is formed between the first ground structure and the second ground structure, a second slot antenna is formed between the second ground structure and the third ground structure, the electric field amplitudes of the first slot antenna and the second slot antenna are equal, there is a magnetic coupling effect between the two slot antennas, the orthogonal electric field components of the two slot antennas form a phase difference of 90°, a pair of spatially orthogonal slot antennas are constructed, a pair of orthogonal equal-amplitude electric field components are generated, and the circular polarization effect of the antenna is achieved. By connecting the first slot antenna to the first lumped element matching network and the second slot antenna to the second lumped element matching network, the resonance mode of the two slot antennas is changed from 1 / 2 wavelength resonance to 1 / 4 wavelength resonance, thereby realizing the miniaturization effect of the antenna. The antenna with the above-mentioned circular polarization and miniaturization characteristics is particularly suitable for small wearable devices such as smart watches. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to make the content of the present application more easily understood, the present application will be further described in detail below according to specific embodiments of the present application and in conjunction with the drawings, in which

[0028] Figure 1 is a back view of a circularly polarized antenna provided by an embodiment of the present application;

[0029] Figure 2 is a front view of a circularly polarized antenna provided by an embodiment of the present application;

[0030] Figure 3 is a structural schematic view of a circularly polarized antenna provided by an embodiment of the present application;

[0031] Figure 4 is a S parameter curve diagram of a circularly polarized antenna provided by an embodiment of the present application before loading a first lumped element matching network and a second lumped element matching network;

[0032] Figure 5 is an axial ratio curve diagram of a circularly polarized antenna provided by an embodiment of the present application before loading a first lumped element matching network and a second lumped element matching network;

[0033] Figure 6 is a S parameter curve diagram of a circularly polarized antenna provided by an embodiment of the present application after loading a first lumped element matching network and a second lumped element matching network;

[0034] Figure 7 is an axial ratio curve diagram of a circularly polarized antenna provided by an embodiment of the present application after loading a first lumped element matching network and a second lumped element matching network;

[0035] Figure 8 is an electric field distribution diagram of a circularly polarized antenna provided by an embodiment of the present application before loading a first lumped element matching network and a second lumped element matching network;

[0036] Figure 9 is an electric field distribution diagram of a circularly polarized antenna provided by an embodiment of the present application after loading a first lumped element matching network and a second lumped element matching network;

[0037] Figure 10 is a directional diagram of a circularly polarized antenna provided by an embodiment of the present application at a frequency point of 1.58 GH.

[0038] The reference signs in the drawings are as follows: 1-metal frame; 2-circuit board; 3-first ground structure; 4-second ground structure; 5-first slot antenna; 6-third ground structure; 7-second slot antenna; 8-first lumped element matching network; 9-second lumped element matching network; 10-fourth ground structure; 11-feeding port; 12-fifth ground structure; 13-first lumped element; 14-second lumped element; 15-third lumped element; 16-fourth lumped element; 17-first microstrip feed line; 18-first short-circuiting member; 19-second short-circuiting member. DETAILED DESCRIPTION

[0039] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present application with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some but not all of the embodiments of the present application. The components of the embodiments of the present application described and shown in the drawings can be arranged and designed in various different configurations.

[0040] In the description of the present application, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", and the like is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship commonly used when the product of the present application is used, or the orientation or positional relationship commonly understood by those skilled in the art, and is only for the convenience of describing the present application and simplifying the description, and does not indicate or imply that the indicated device or element must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application.

[0041] The "first", "second", and the like of the present application are only used to distinguish in description and do not have special meanings.

[0042] In the description of the present application, it should be noted that, unless otherwise explicitly specified and limited, the terms "arrangement", "installation" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be directly connected, or indirectly connected through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0043] Embodiment

[0044] The present embodiment provides a circularly polarized antenna suitable for intelligent terminal equipment, especially intelligent terminal equipment with a metal frame. Referring to Figures 1-3 The circularly polarized antenna provided by the present embodiment comprises a metal frame 1, an internal circuit board 2 is arranged in the metal frame 1, the metal frame 1 surrounds the circuit board 2 and the circuit board 2 is arranged spaced apart from the metal frame 1, so that there is a gap between the circuit board 2 and the metal frame 1.

[0045] In the present embodiment, the metal frame 1 is preferably a full-closed metal frame made of metal material, which is part of the intelligent terminal equipment, and the circuit board 2 is a printed circuit board (PCB) for carrying circuits and electronic components.

[0046] A first ground structure 3 is arranged in the gap between the metal frame 1 and the circuit board 2, and the first ground structure 3 is electrically connected with the metal frame 1. A second ground structure 4 is also arranged in the gap between the metal frame 1 and the circuit board 2, and the second ground structure 4 is arranged in a spaced manner with the first ground structure 3, and the second ground structure 4 is also electrically connected with the metal frame 1, and a first gap antenna 5 is formed between the first ground structure 3 and the second ground structure 4.

[0047] A third ground structure 6 is also arranged in the gap between the metal frame 1 and the circuit board 2, and the third ground structure 6 is arranged in a spaced manner with the first ground structure 3 and the second ground structure 4, and the third ground structure 6 is electrically connected with the metal frame 1, and a second gap antenna 7 is formed between the third ground structure 6 and the second ground structure 4. The electric fields of the first gap antenna 5 and the second gap antenna 7 satisfy the characteristics of equal amplitude and 90° phase difference.

[0048] The first gap antenna 5 is connected with a first lumped element matching network 8, and the second gap antenna 7 is connected with a second lumped element matching network 9. After the above-mentioned lumped element matching networks are loaded on the first gap antenna 5 and the second gap antenna 7, when the resonances are near the working frequency points, the characteristics of equal amplitude and 90° phase difference of the electric fields of the first gap antenna 5 and the second gap antenna 7 can be satisfied.

[0049] The circularly polarized antenna provided in the embodiment is used for the circularly polarized performance requirement of the positioning antenna of the smart terminal device with a metal frame, and the uninterrupted metal frame of the terminal device is used to obtain a circularly polarized positioning antenna, so that the space area of the smart terminal device is maximally used, and the radiation efficiency of the antenna is improved. Specifically, the circularly polarized antenna provided in the embodiment is arranged by arranging the first ground structure 3, the second ground structure 4, and the third ground structure 6 in the gap between the metal frame 1 and the circuit board 2, forming the first gap antenna 5 between the first ground structure 3 and the second ground structure 4, and forming the second gap antenna 7 between the second ground structure 4 and the third ground structure 6, the electric field amplitudes of the first gap antenna 5 and the second gap antenna 7 are equal, there is a magnetic coupling effect between the two gap antennas, the orthogonal electric field components of the two gap antennas form a 90° phase difference, a pair of spatially orthogonal gap antennas are constructed, a pair of orthogonal equal-amplitude electric field components are generated, and the circular polarization effect of the antenna is realized. By connecting the first gap antenna 5 with the first lumped element matching network 8 and connecting the second gap antenna 7 with the second lumped element matching network 9, the resonant mode of the two gap antennas can be changed from 1 / 2 wavelength resonance to 1 / 4 wavelength resonance, the resonant frequency point of the gap antenna is matched to the required working frequency point, and the miniaturization effect of the antenna is realized. The antenna with the above-mentioned circular polarization and miniaturization characteristics is particularly suitable for small wearable devices such as smart watches, solves the problems that the existing smart watches with metal frames are difficult to design circularly polarized antennas and the positioning timing signal is weak, and significantly improves the performance and user experience of the product.

[0050] As Figure 1 shown, the circularly polarized antenna provided by the embodiment further comprises a fourth grounding structure 10, the circuit board 2 is connected with a feeding port 11, the fourth grounding structure 10 and the first lumped element matching network 8 are connected to the feeding port 11, and meanwhile, the first lumped element matching network 8 is also connected to the metal frame 1. The circularly polarized antenna further comprises a fifth grounding structure 12, the fifth grounding structure 12 is connected to the second lumped element matching network 9, and the second lumped element matching network 9 is also connected to the metal frame 1.

[0051] The first slot antenna 5 and the second slot antenna 7 have electromagnetic coupling effect and can exchange energy with each other, so that only one feeding port 11 is needed, that is, only the first slot antenna 5 needs to be excited when feeding, and energy can be transmitted to the second slot antenna 7 through coupling, and meanwhile, the amplitude and phase of the electric field component required for circular polarization are generated through energy exchange by coupling, and no additional phase shifter power divider is needed, so that the structure is simple, the circular polarization performance is stable, and the above-mentioned single feeding mode greatly simplifies the antenna design and reduces the cost.

[0052] In the embodiment, the first grounding structure 3, the second grounding structure 4, the third grounding structure 6, the fourth grounding structure 10 and the fifth grounding structure 12 are all grounding sheets.

[0053] As Figure 1 shown, in the circularly polarized antenna provided by the embodiment, the first lumped element matching network 8 is preferably an L-shaped matching network, the first lumped element matching network 8 is loaded with a first lumped element 13 and a second lumped element 14, one end of the first lumped element matching network 8 is connected to the metal frame 1, and the other end is connected to the fourth grounding structure 10 and the feeding port 11. The first lumped element 13 and the second lumped element 14 are capacitive or inductive devices.

[0054] The second lumped element matching network 9 is also preferably an L-shaped matching network, the second lumped element matching network 9 is loaded with a third lumped element 15 and a fourth lumped element 16, and the third lumped element 15 and the fourth lumped element 16 are capacitive or inductive devices. One end of the second lumped element matching network 9 is connected to the metal frame 1, and the other end is connected to the fifth grounding structure 12.

[0055] In practical applications, the resonant lengths of the first slot antenna 5 and the second slot antenna 7 are much shorter than the resonant wavelength of the GPS frequency band, therefore, the first lumped element matching network 8 and the second lumped element matching network 9 are adopted, and the first lumped element matching network 8 and the second lumped element matching network 9 adopt L-type matching networks. The L-type matching network has a simple structure, and after the first lumped element matching network 8 and the second lumped element matching network 9 are loaded, the resonant mode of the first slot antenna 5 and the second slot antenna 7 changes from 1 / 2 wavelength resonance to 1 / 4 wavelength resonance, so that the resonant frequency point of the slot antenna can be matched to the required operating frequency point. In addition, by loading the lumped element, the resonant frequency of the antenna can be flexibly adjusted under the condition that the size of the metal frame 1 is small and cannot be changed, so that the antenna can work in the GNSS frequency band, and the miniaturization of the antenna is fully realized, which is more suitable for wearable devices such as smart watches.

[0056] Further, the fourth ground structure 10 is also electrically connected with a first microstrip feed line 17, and the fourth ground structure 10 is connected to the feed port 11 through the first microstrip feed line 17. The fifth ground structure 12 is electrically connected with a second microstrip feed line (not shown in the figure). The first microstrip feed line 17 and the second microstrip feed line are both 50-ohm microstrip feed lines.

[0057] Please refer to Figures 1-3 The circularly polarized antenna provided in the embodiment has a metal frame 1 which is an uninterrupted rectangular frame, and a circuit board 2 which is a rectangular board. The metal frame 2 surrounds the outside of the circuit board 2, and a rectangular slot is formed between the metal frame 1 and the circuit board 2. As shown in the figure, the first ground structure 3 is arranged at a first corner of the rectangular slot, and the second ground structure 4 is arranged at a second corner of the rectangular slot. The first corner and the second corner are arranged adjacent to each other along a short side of the rectangular slot, so that the short side of the rectangular slot forms the first slot antenna 5. The third ground structure 6 is arranged adjacent to a third corner of the rectangular slot, and the third corner and the second corner are arranged opposite to each other along a long side of the rectangular slot. The long side of the rectangular slot between the third ground structure 6 and the second ground structure 4 forms the second slot antenna 7.

[0058] The first slot antenna 5 and the second slot antenna 7 have an included angle of 75-105°. In the embodiment, as shown in the figure, the first slot antenna 5 and the second slot antenna 7 are respectively located on the adjacent short side and long side of the rectangular slot, so that the first slot antenna 5 and the second slot antenna 7 have an included angle of 90°. In the embodiment, preferably, the operating frequency point of the circularly polarized antenna is 1.58 GHz, the size of the metal frame 1 is 37 mm x 46 mm, the size of the circuit board 2 is 31.6 mm x 40 mm, the width of the first slot antenna 5 is 1.7 mm, the width of the second slot antenna 7 is 2 mm, and the lengths of the first slot antenna 5 and the second slot antenna 7 are the same, both being 35 mm.

[0059] AsFigures 2-3 As shown, the inner space of the first slot antenna 5 is further provided with a first short-circuit member 18, and the inner space of the second slot antenna 7 is further provided with a second short-circuit member 19, the first short-circuit member 18 and the second short-circuit member 19 are used to connect the metal frame 1 with the ground plane of the circuit board 2.

[0060] The embodiment also provides a wearable device comprising the circularly polarized antenna described above, and in the embodiment, the wearable device is preferably a smart watch.

[0061] Experimental example

[0062] 1. The S parameter curve and axial ratio curve before and after loading the first lumped element matching network and the second lumped element matching network are tested, and the test results are as shown in Figures 4-7 .

[0063] Among them, Figure 4 is the S parameter curve of the circularly polarized antenna before loading the first lumped element matching network and the second lumped element matching network, Figure 5 is the axial ratio curve of the circularly polarized antenna before loading the first lumped element matching network and the second lumped element matching network. As can be seen from Figures 4-5 , before loading the lumped element matching network, the antenna structure is at 4.06GHz.

[0064] Figure 6 is the S parameter curve of the circularly polarized antenna after loading the first lumped element matching network and the second lumped element matching network, Figure 7 is the axial ratio curve of the circularly polarized antenna after loading the first lumped element matching network and the second lumped element matching network. As can be seen from the antenna reflection coefficient results of Figure 6 , the -10dB return loss of the antenna can cover 1.562-1.591GHz, and as can be seen from Figure 7 , the axial ratio performance of the antenna at 1.58GHz is the best.

[0065] 2. The antenna electric field distribution before and after loading the first lumped element matching network and the second lumped element matching network is tested, and the test results are as shown in Figures 8-9 .

[0066] Figure 8 is the electric field distribution before loading the first lumped element matching network and the second lumped element matching network, Figure 9 is the electric field distribution after loading the first lumped element matching network and the second lumped element matching network, as can be seen from the figure, after loading the lumped element, the resonant wavelength of the antenna becomes shorter: the resonant mode of the antenna before loading is 1 / 2 wavelength resonance, and the resonant mode of the antenna after loading is 1 / 4 wavelength resonance, thereby realizing the miniaturization effect of the antenna.

[0067] 3. The radiation pattern of the circularly polarized antenna provided by the test example at 1.58 GHz is shown in the following table. Figure 10

[0068] Figure 10 is the cross-sectional radiation pattern of the circularly polarized antenna at 1.58 GHz, φ = 0° and φ = 90°. As can be seen from the figure, the radiation pattern of the antenna at this frequency point can maintain stable edge radiation.

[0069] As can be seen from the test results, the circularly polarized antenna provided by the above-mentioned embodiments, in combination with the metal frame of the wearable smart terminal device, not only has the advantages of simple form, compact structure and small size design of wearable devices, but also has the advantage of stable performance.

[0070] Obviously, the above-mentioned embodiments are only examples for the sake of clarity, and are not a limitation on the embodiments. For those skilled in the art, other different forms of changes or variations can be made on the basis of the above description. It is not necessary and impossible to enumerate all the embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the present application.​

Claims

1. A circularly polarized antenna, characterized by, include: Metal frame; A circuit board is disposed inside the metal frame and spaced apart from the metal frame, with a gap between the circuit board and the metal frame; A first grounding structure is disposed within the gap and electrically connected to the metal frame; A second grounding structure is disposed within the gap, spaced apart from the first grounding structure, and electrically connected to the metal frame. A first gap antenna is formed between the second grounding structure and the first grounding structure. A third grounding structure is disposed within the gap, spaced apart from the first grounding structure and the second grounding structure, and electrically connected to the metal frame. A second slot antenna is formed between the third grounding structure and the second grounding structure. The electric field amplitudes of the first slot antenna and the second slot antenna are equal, and their phases differ by 90°. The first slot antenna is connected to a first lumped element matching network, and the second slot antenna is connected to a second lumped element matching network. The first lumped element matching network is an L-shaped matching network, and the first lumped element matching network is loaded with a first lumped element and a second lumped element. The second lumped element matching network is an L-shaped matching network, and the second lumped element matching network is loaded with a third lumped element and a fourth lumped element. It also includes a fourth grounding structure. The circuit board is connected to a feed port. The fourth grounding structure and the first lumped element matching network are connected to the feed port. The first lumped element matching network is also connected to the metal frame. There is an electromagnetic coupling effect between the first slot antenna and the second slot antenna, which can exchange energy with each other. When feeding, only the first slot antenna needs to be excited, and energy can be transferred to the second slot antenna through coupling. Energy exchange through coupling generates the amplitude and phase of the electric field component required for circular polarization.

2. The circularly polarized antenna of claim 1, wherein, It also includes a fifth grounding structure, which is connected to the second lumped element matching network, which is also connected to the metal frame.

3. The circularly polarized antenna of claim 2, wherein, The first slot antenna and the second slot antenna have an angle of 75-105°.

4. The circularly polarized antenna of claim 3, wherein, The first lumped element, the second lumped element, the third lumped element, and the fourth lumped element are all capacitors or inductors.

5. The circularly polarized antenna of claim 4, wherein, The metal frame is a rectangular frame, the circuit board is a rectangular board, and a rectangular gap is formed between the metal frame and the circuit board; the first grounding structure is disposed at the first corner of the rectangular gap, the second grounding structure is disposed at the second corner of the rectangular gap, the first corner and the second corner are disposed adjacent to each other along the short side of the rectangular gap, and the third grounding structure is disposed adjacent to the third corner of the rectangular gap, the third corner and the second corner are disposed adjacent to each other along the long side of the rectangular gap.

6. The circularly polarized antenna of claim 5, wherein, The fourth grounding structure is also electrically connected to the first microstrip feed line, and the fourth grounding structure is connected to the power supply port through the first microstrip feed line; the fifth grounding structure is connected to the second microstrip feed line.

7. A wearable device, comprising: Including the circularly polarized antenna as described in any one of claims 1-6.

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