Mobile phone rear cover antenna based on artificial surface plasmon

Abstract

The invention discloses a mobile phone rear cover antenna based on artificial surface plasmon, and mainly solves the problems of high profile height and large occupied space of a mobile phone rear cover antenna in the prior art. Comprising a first printed metal layer composed of a coplanar waveguide transmission line, a transition structure and an artificial surface plasmon leaky-wave antenna, and a second printed metal layer and a third printed metal layer which are composed of two square metal patches, the first metal layer is printed on the upper surface of a first dielectric layer, and the second metal layer is printed on the lower surface of a second dielectric layer. The leaky-wave antenna is realized by installing a parasitic patch on an artificial surface plasmon transmission line. The coplanar waveguide transmission line comprises a central conduction band and a floor; and the second magnetic conductor floor and the third magnetic conductor floor are respectively printed on the upper and lower surfaces of the second dielectric layer to form an artificial magnetic conductor floor covering the working frequency band of the antenna. The antenna profile height can be effectively reduced by using the artificial magnetic conductor floor, and meanwhile, the interaction between the antenna and a human body is reduced; the antenna can be used for mobile phone rear cover antenna design.

Description

Technical Field

[0001] The present invention belongs to the technical field of antennas, and further relates to the technology of low-profile antennas. Specifically, it is a planar antenna based on artificial surface plasmons, which can be used for the design of mobile phone back cover antennas. Background Art

[0002] With the development of mobile communication technology, the number of electromagnetic wave frequency bands required for mobile phone communication is increasing. Therefore, more antennas are needed in mobile phones to meet the growing demand for antenna frequency bands. At the same time, as consumers' requirements for the appearance and performance of mobile phones become increasingly strict, the mobile phones launched by various mobile phone manufacturers are gradually becoming lighter and thinner, the proportion of the screen and the battery is also increasing, the mobile phone frame is gradually becoming narrower, and the clearance between the mobile phone frame and the screen is gradually becoming smaller. Currently, most mobile phone antennas are designed on or near the mobile phone frame. Therefore, in the face of the increasingly complex design environment on the frame, people begin to focus on the places outside the mobile phone frame for antenna design. At this time, the large area of unused space on the mobile phone back cover has become the focus of attention. Although the area where the mobile phone back cover can be designed with antennas is large, limited by the requirement of device thinning, the antenna profile height (i.e., the thickness of the antenna structure perpendicular to the back cover) needs to be controlled at an extremely low level. Usually, the antenna profile height of the mobile phone back cover antenna does not exceed 1.5 mm. Therefore, it is necessary to design a low-profile antenna that meets the requirements of wireless communication as the mobile phone back cover antenna.

[0003] In recent years, artificial surface plasmons have attracted much attention due to their low profile and the characteristic of being integrable on flexible surfaces. In the field of antennas, artificial surface plasmons are often used in the design of planar transmission lines and also in the design of leaky-wave antennas. For the design of low-profile antennas based on artificial surface plasmons, researchers have proposed many methods. For example, in the paper "Spoof Surface Plasmon Polariton Leaky-Wave Antennas Using Periodically Loaded Patches Above PEC and AMC GroundPlanes" published by Zhang QL, Zhang Q, and Chen Y in the IEEE Antennas and Wireless Propagation Letters, Vol. 16, pp. 3014 - 3017, 2017, a leaky-wave antenna was proposed by installing metal patches on both sides of the artificial surface plasmon transmission line. By changing the size of the patches, the operating frequency band of the antenna can be controlled. The operating frequency band of this antenna is in the range of 4.5 GHz to 6.5 GHz. The artificial magnetic conductor floor and the perfect electric conductor floor were respectively placed under the antenna for comparison. The results show that the profile height of the antenna using the artificial magnetic conductor floor is much smaller than that of the antenna using the perfect electric conductor floor, which is due to the in-phase reflection of electromagnetic waves by the artificial magnetic conductor. Moreover, the return loss and gain of the antennas using the two floors are close. However, this antenna does not consider operating in the frequency band required for wireless communication, and since the operating bandwidth of the artificial magnetic conductor is less than the operating bandwidth of the antenna, the gain of this antenna near 5.7 GHz within the operating frequency band is significantly lower than that in other operating frequency bands. Summary of the Invention

[0004] The purpose of the present invention is to address the deficiencies of the above-mentioned prior art and propose a mobile phone back cover antenna based on artificial surface plasmons to solve the problem of limited application of mobile phone back cover antennas due to high profile and narrow bandwidth. First, by installing metal patches of different sizes on both sides of the artificial surface plasmon transmission line, the operating bandwidth of the antenna is increased. Then, broadband processing is performed on the artificial magnetic conductor floor to make it cover the operating frequency band of the antenna. The present invention enables the mobile phone back cover antenna to cover the frequency band required for wireless communication and reduces the antenna profile height by using the artificial magnetic conductor floor, significantly improving the application performance of the mobile phone back cover antenna.

[0005] To achieve the above object, the technical solution of the present invention includes the following:

[0006] A mobile phone back cover antenna based on artificial surface plasmons, comprising a mobile phone back cover, a frame and an antenna; the antenna includes a first printed metal layer 1, a first dielectric layer 2, an air layer 3, a second printed metal layer 4, a second dielectric layer 5 and a third printed metal layer 6 from top to bottom; wherein the first printed metal layer 1 is printed on the upper surface of the first dielectric layer 2 to form an antenna structure based on artificial surface plasmons; the second printed metal layer 4 and the third printed metal layer 6 are respectively printed on the upper and lower surfaces of the second dielectric layer 5, and the three form an artificial magnetic conductor floor structure; the antenna is installed at a corner of the mobile phone back cover and is integrally designed with the mobile phone back cover;

[0007] The above-mentioned first printed metal layer 1 is composed of a coplanar waveguide transmission line 11, a transition structure 12 and an artificial surface plasmon leaky wave antenna; wherein the artificial surface plasmon leaky wave antenna is composed of an artificial surface plasmon transmission line 13 and first circular metal patches 14 and second circular metal patches 15 with different shapes on both sides thereof;

[0008] The above-mentioned air layer 3 fixes the first dielectric layer 2 and the second dielectric layer 5 through glue distributed at the edge part of the air layer;

[0009] The above-mentioned second printed metal layer 4 is composed of two parts of square metal patches, and the patch sizes and spacings of the first part and the second part are different, that is, the size of the first part is smaller than that of the second part, and the row spacing of the first part, the row spacing of the second part and the spacing between the two parts decrease in sequence; the square metal patches correspond to the circular metal patches in the first printed metal layer 1 in size, that is, a square metal patch with a smaller size and a larger spacing is placed correspondingly under a larger circular metal patch;

[0010] Furthermore, the above-mentioned coplanar waveguide transmission line 11 includes a center conductor strip and a floor, wherein the center conductor strip is connected to the artificial surface plasmon transmission line 13 through the transition structure 12, and the floor is symmetrically distributed on both sides of the center conductor strip.

[0011] Compared with the prior art, the present invention has the following advantages:

[0012] First, since circular metal patches with different sizes and spacings are installed on both sides of the artificial surface plasmon transmission line in the present invention, it has a larger bandwidth compared with the traditional artificial surface plasmon leaky wave antenna, and the working frequency band of the antenna can be adjusted by changing the radius and spacing of the circular patches during the design process;

[0013] Second, since the square metal patches used in the artificial magnetic conductor floor of the present invention are divided into upper and lower parts with different sizes and spacings, the operating frequency band of the artificial magnetic conductor floor can be changed by adjusting the size of the square metal patches, so as to cover the operating frequency band of the antenna and achieve the purpose of improving its operating bandwidth;

[0014] Third, the operating frequency band of the antenna of the present invention is designed to cover certain frequency bands of mobile phone wireless communication, so it is more suitable for use in mobile phone wireless communication. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the overall structure of the present invention.

[0016] Figure 2 It is a schematic diagram of the structure of the mobile phone back cover and the frame in the present invention.

[0017] Figure 3 It is a schematic diagram of the antenna hierarchical structure in the present invention.

[0018] Figure 4 It is a schematic diagram of the antenna cross-sectional structure in the present invention.

[0019] Figure 5 It is Figure 3 a schematic diagram of the structure of the first printed metal layer 1 printed above the first dielectric layer 2 in

[0020] Figure 6 It is Figure 3 a schematic diagram of the structure of the second printed metal layer 4 printed above the second dielectric layer 5 in

[0021] Figure 7 It is a graph of the return loss characteristics in an embodiment of the present invention.

[0022] Figure 8 It is a graph of the antenna efficiency in an embodiment of the present invention.

[0023] Figure 9 It is the normalized radiation pattern of the E-plane and H-plane of the antenna in an embodiment of the present invention; where (a) is the normalized radiation pattern of the E-plane of the antenna of the present invention at 26.5 GHz; (b) is the normalized radiation pattern of the H-plane of the antenna of the present invention at 26.5 GHz. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0024] The present invention will be further described below with reference to the accompanying drawings:

[0025] Embodiment 1: Refer to Figures 1-3, a mobile phone back cover antenna based on artificial surface plasmon proposed by the present invention includes a mobile phone back cover, a frame and an antenna. The antenna includes, from top to bottom, a first printed metal layer 1, a first dielectric layer 2, an air layer 3, a second printed metal layer 4, a second dielectric layer 5 and a third printed metal layer 6. The first printed metal layer 1 is printed on the upper surface of the first dielectric layer 2 to form an artificial surface plasmon antenna structure. The second printed metal layer 4 and the third printed metal layer 6 are respectively printed on the upper and lower surfaces of the second dielectric layer 5, and the three form an artificial magnetic conductor floor structure. The antenna is installed in a corner of the mobile phone back cover and is integrally designed with the mobile phone back cover. In this embodiment, both the mobile phone back cover and the frame are made of dielectric materials. Preferably, the relative dielectric constant of the mobile phone back cover material is ε1 = 4.38, and the relative dielectric constant of the mobile phone frame material is ε2 = 3.55.

[0026] The above-mentioned first printed metal layer 1 is composed of a coplanar waveguide transmission line 11, a transition structure 12 and an artificial surface plasmon leaky wave antenna. The artificial surface plasmon leaky wave antenna is composed of an artificial surface plasmon transmission line 13 and first and second circular metal patches 14 and 15 with different shapes on both sides thereof.

[0027] The above-mentioned air layer 3 fixes the first dielectric layer 2 and the second dielectric layer 5 through glue distributed at the edge of the air layer.

[0028] The above-mentioned second printed metal layer 4 is composed of two parts of square metal patches, and the patch sizes and spacings of the first part and the second part are different, that is, the size of the first part is smaller than that of the second part, and the row spacing of the first part, the row spacing of the second part and the spacing between the two parts decrease in sequence. The square metal patches correspond to the circular metal patches in the first printed metal layer 1 in size, that is, a smaller and more spaced square metal patch is placed corresponding to the larger circular metal patch.

[0029] Furthermore, the coplanar waveguide transmission line 11 includes a center conductor strip and a ground plane. The center conductor strip is connected to the artificial surface plasmon transmission line 13 through a transition structure 12, and the ground planes are symmetrically distributed on both sides of the center conductor strip. The coplanar waveguide transmission line 11 is used to connect the artificial surface plasmon transmission line 13 with a single-conductor structure to the coaxial transmission line with a double-conductor structure in a microwave anechoic chamber, so as to realize the excitation and testing of the antenna in kind. In this embodiment, the length of the coplanar waveguide transmission line 11 is not less than 4 mm, the width of the center conductor strip is 1.5 mm, and the distance between the center conductor strip and the ground planes on both sides is 0.1 mm. The transition structure 12 is used to realize the impedance matching between the coplanar waveguide transmission line 11 and the artificial surface plasmon transmission line 13. The distance between the ground planes on both sides and the center conductor strip gradually increases, and the depth of the groove on the center conductor strip gradually becomes deeper. In this embodiment, the designed length of the transition structure is not less than 17.5 mm, and the width of the widest part of the ground plane is 10 mm. Preferably, the length of the groove is set to 1.5 mm, the depth of the deepest part of the groove is 0.8 mm, and the length and depth of the groove are used to determine the operating frequency band of the artificial surface plasmon transmission line 13. The artificial surface plasmon transmission line 13 is composed of no less than 27 H-shaped artificial surface plasmon units. The first circular metal patch 14 and the second circular metal patch 15 form a leaky wave antenna by changing the impedance of the artificial surface plasmon transmission line 13 through electrical coupling with the transmission line. In this embodiment, the length of the artificial surface plasmon transmission line 13 is not less than 67.5 mm. The length of the H-shaped artificial surface plasmon unit is not less than 2.5 mm, and the width is not less than 3.5 mm. The first circular metal patch 14 and the second circular metal patch 15 located on both sides of the artificial surface plasmon transmission line 13 have a diameter determined by 1 / 4 wavelength corresponding to the center point of the operating frequency band of the transmission line. The center distance between two adjacent circular metal patches on the same side is not greater than 5.5 mm, and the center distance between adjacent patches on both sides is not greater than 10 mm.

[0030] In this embodiment, for the first printed metal layer 1, the second printed metal layer 4, and the third printed metal layer 6, the printed metal materials all include common circuit board metal materials such as copper, aluminum, tin, and nickel. The thickness is H4, and the value range is 0.0175 mm to 0.035 mm. The thickness of the air layer 3 is the same as that of the glue, and the value is 0.05 to 0.1 mm. The total cross-sectional height of the antenna is 0.95 to 1.1 mm. The dielectric constants of the dielectric materials used for the first dielectric layer 2 and the second dielectric layer 5 are both ε3 = 3.55. The thicknesses are H1 and H3 respectively, where H1 is 0.5 to 0.55 mm and H3 is 0.4 to 0.45 mm.

[0031] Embodiment 2: The overall structure of the mobile phone back cover antenna proposed in this embodiment is the same as that in Embodiment 1. Now refer to Figures 1-6, specific dimensional parameters and material properties are selected, and examples are given to further describe the present invention in detail.

[0032] Referring to Figure 1 , for the mobile phone back cover antenna proposed by the present invention, the antenna is installed in a corner of the mobile phone back cover and is integrally designed with the mobile phone back cover.

[0033] Referring to Figure 2 , for the mobile phone model adopted in this embodiment, the length L is 162 mm, the width W is 75 mm, and the thickness H is 8.4 mm; this size is measured based on the size of a certain smart phone in the market. Both the mobile phone back cover and the frame are dielectric materials, where the relative permittivity ε1 of the mobile phone back cover material is 4.38, and the relative permittivity ε2 of the mobile phone frame material is 3.55.

[0034] Referring to Figure 3 , the antenna structure in this design includes a first printed metal layer 1, a first dielectric layer 2, an air layer 3, a second printed metal layer 4, a second dielectric layer 5, and a third printed metal layer 6 from top to bottom. Among them, the first printed metal layer 1 is printed on the upper surface of the first dielectric layer 2 to form an artificial surface plasmon antenna structure; the second printed metal layer 4 is printed on the upper surface of the second dielectric layer 5, and the third printed metal layer 6 is printed on the lower surface of the second dielectric layer 5, and the three together form an artificial magnetic conductor floor structure. In this embodiment, copper is preferably used as the printed metal material, and the relative permittivity ε3 of the dielectric material used for the dielectric layer is 3.55. There is a small amount of glue distributed at the edge of the air layer 3, which is used to fix the first dielectric layer 2 and the second dielectric layer 5, and placing the glue at the edge can effectively reduce the influence of the glue on the antenna radiation.

[0035] Referring to Figure 4 , as can be seen from the cross-sectional view of the antenna structure in this design, the antenna consists of five parts from top to bottom. In this embodiment, for Figure 3 the thickness H1 of the first dielectric layer 2 described in is preferably 0.508 mm, the thickness H3 of the second dielectric layer 5 is preferably 0.406 mm, the thickness of the air layer 3 is preferably 0.1 mm, and the thickness H4 of the printed metal layer is preferably 0.0175 mm. Therefore, the total cross-sectional height of this antenna is about 1.049 mm.

[0036] Referring to Figure 3 and Figure 5, the first printed metal layer 1 printed above the first dielectric layer 2 consists of the following parts: a coplanar waveguide transmission line 11, a transition structure 12, and a metasurface leaky wave antenna. The metasurface leaky wave antenna is composed of a metasurface transmission line 13 and circular metal patches 14 and 15 with different shapes on both sides thereof. The coplanar waveguide transmission line is used to connect the metasurface transmission line with a single-conductor structure to a coaxial transmission line with a double-conductor structure. In this embodiment, it is preferably that the length L1 of the coplanar waveguide transmission line is 4 mm, the width W1 of the center conductor strip is 1.5 mm, and the distance D1 between the center conductor strip and the two ground planes on both sides is 0.1 mm; the transition structure is used to realize the impedance matching design between the coplanar waveguide transmission line and the metasurface transmission line. The distance between the ground planes on both sides and the center conductor strip gradually increases, and the depth of the groove on the center conductor strip gradually becomes deeper. In this embodiment, it is preferably that the length L2 of the transition structure is 17.5 mm, and the width W2 at the widest part of the ground plane is 10 mm; on the right side of the transition structure is a leaky wave antenna based on the metasurface. The leaky wave antenna is composed of a metasurface transmission line and metal patches on both sides thereof. The circular metal patch near the transmission line can have electrical coupling with the transmission line, change the impedance of the transmission line, and form a leaky wave antenna; in this embodiment, it is preferably that the metasurface transmission line is composed of 27 H-shaped metasurface units. The grooves on the patches can confine the free electrons in the metal, so that the wave in space is converted from the plane wave mode to the metasurface mode confined near the transmission line, and then coupled with the circular metal patch near the transmission line to generate radiation. In this embodiment, it is preferably that the length L3 of the metasurface transmission line is 67.5 mm, the length L4 of the H-shaped metasurface unit is 2.5 mm, the width W3 is 3.5 mm, the groove length L5 is 1.5 mm, the depth W4 is 0.8 mm, the diameter D2 of the circular metal patch on the upper side of the transmission line is 2.4 mm, the diameter D3 of the circular metal patch on the lower side of the transmission line is 2 mm, the center distance D4 between two adjacent patches is 5.5 mm, and the center distance D5 between the patches on both sides of the transmission line is 10 mm. This solution of using circular metal patches of different sizes in the upper and lower parts can increase the working bandwidth of the leaky wave antenna.

[0037] Refer to Figure 6, the second printed metal layer 4 printed above the second dielectric layer 5 is composed of upper and lower square metal patches, and the sizes and spacings of the upper and lower square metal patches are different; this is an artificial magnetic conductor structure designed for the operating frequency band of the antenna with a working bandwidth consistent with the antenna's operating bandwidth. This artificial magnetic conductor structure can reflect electromagnetic waves in the opposite direction, so it can effectively reduce the profile height of the antenna. Among them, the square metal patches used for the upper half of the artificial magnetic conductor floor are smaller in size. In this embodiment, it is preferably that the length L7 of this part of the patch is 2.3 mm, the spacing D6 is 2.8 mm, and a total of 2 rows and 17 columns are placed; the square metal patches used for the lower half of the artificial magnetic conductor floor are larger in size. In this embodiment, it is preferably that the length L8 of this part of the patch is 2.6 mm, the spacing D7 is 2.6 mm, and a total of 2 rows and 17 columns are placed. The spacing D8 between the metal patches in the second row and the third row is 2.1 mm, the length L6 of the artificial magnetic conductor floor is 89 mm, and the width W5 is 10 mm.

[0038] The effects of the present invention can be further illustrated in combination with the simulation results:

[0039] 1. Simulation conditions:

[0040] The simulation experiment of the present invention is carried out using the commercial simulation software CST Microwave Studio.

[0041] 2. Simulation content:

[0042] Simulation 1, using the commercial simulation software CST Microwave Studio to simulate and calculate the return loss parameters of the second embodiment of the present invention, and the results are as Figure 7 shown.

[0043] From Figure 7 it can be seen that with the return loss < -10 dB as the standard, the working bandwidth of the mobile phone back cover antenna based on artificial surface plasmons in the second embodiment covers 24.25 GHz to 29.5 GHz. This working frequency band includes the n257 and n258 frequency bands in the 5G millimeter wave communication frequency band, and the relative bandwidth is 20%.

[0044] Simulation 2, using the commercial software CST Microwave Studio to simulate and calculate the radiation efficiency and total efficiency of the antenna of the present invention, and the results are as Figure 8 shown.

[0045] From Figure 8 it can be seen that the total efficiency of the antenna of the present invention in the working frequency band of 24.25 GHz to 29.5 GHz is higher than -1.5 dB. After calculation, the average total efficiency of the antenna in the working frequency band is -0.97 dB.

[0046] Simulation 3: Use the commercial software CST Microwave Studio to simulate the antenna gain pattern of the present invention, perform normalization processing, and then compare it with the normalized pattern of the antenna measured in the anechoic chamber. The results are as Figure 9 shown. As can be seen from Figure 9 (a) and (b) in, when the antenna of the present invention operates at 26.5 GHz, the distribution of the radiation pattern in the upper half of the E-plane is significantly greater than that in the lower half, indicating that the artificial magnetic conductor floor below the antenna plays a role in reflecting the antenna radiation in the same phase. In addition, the simulation results are basically consistent with the test results.

[0047] The above simulation results show that the antenna of the embodiment of the present invention effectively reduces the profile height of the antenna and enables the antenna to have a large operating bandwidth by respectively performing broadband and miniaturization designs on the artificial surface plasmon leaky wave antenna and the artificial magnetic conductor floor. Its operating frequency band covers the n257 and n258 bands of 5G millimeter wave communication. And the simulation results are in good agreement with the measured results, verifying the correctness of the embodiment of the present invention.

[0048] The parts not described in detail in the present invention belong to the common general knowledge of those skilled in the art.

[0049] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Obviously, for those skilled in the art, after understanding the content and principle of the present invention, various modifications and changes in form and details may be made without departing from the principle and structure of the present invention. However, these modifications and changes based on the idea of the present invention are still within the scope of the claims of the present invention.

Claims

1. A mobile phone back cover antenna based on artificial surface plasmons, comprising a mobile phone back cover, a frame and an antenna, characterized in that: The antenna from top to bottom includes a first printed metal layer (1), a first dielectric layer (2), an air layer (3), a second printed metal layer (4), a second dielectric layer (5), and a third printed metal layer (6); wherein the first printed metal layer (1) is printed on the upper surface of the first dielectric layer (2) to form an antenna structure based on artificial surface plasmon; the second printed metal layer (4) and the third printed metal layer (6) are respectively printed on the upper and lower surfaces of the second dielectric layer (5), and the three form an artificial magnetic conductor floor structure; the antenna is installed at a corner of the mobile phone back cover and is integrally designed with the mobile phone back cover; The first printed metal layer (1) consists of a coplanar waveguide transmission line (11), a transition structure (12), and an artificial surface plasmon leaky wave antenna; wherein the artificial surface plasmon leaky wave antenna is composed of an artificial surface plasmon transmission line (13) and first and second circular metal patches (14) and (15) with different shapes on both sides thereof; For the air layer (3), the first dielectric layer (2) and the second dielectric layer (5) are fixed by glue distributed at the edge part of the air layer; The second printed metal layer (4) consists of two parts of square metal patches, and the patch sizes and spacings of the first part and the second part are different, that is, the size of the first part is smaller than that of the second part, and the row spacing of the first part, the row spacing of the second part, and the spacing between the two parts decrease in sequence; the square metal patches correspond to the circular metal patches in the first printed metal layer (1) in size, that is, a square metal patch with a smaller size and a larger spacing is placed correspondingly under a larger circular metal patch; The coplanar waveguide transmission line (11) includes a center conductor strip and a ground plane. The center conductor strip is connected to the artificial surface plasmon transmission line (13) through the transition structure (12), and the ground planes are symmetrically distributed on both sides of the center conductor strip.

2. The mobile phone back cover antenna according to claim 1, wherein: Both the mobile phone back cover and the frame are made of dielectric materials, wherein the dielectric constant of the mobile phone back cover material is ε1 = 4.38, and the dielectric constant of the mobile phone frame material is ε2 = 3.

55.

3. The mobile phone back cover antenna according to claim 1, characterized in that: The printed metal materials of the first printed metal layer (1), the second printed metal layer (4), and the third printed metal layer (6) all include copper, aluminum, tin, and nickel; the thickness of each is H4, and the value range is 0.0175 mm to 0.035 mm; the thickness of the air layer (3) is the same as that of the glue, and the value is 0.05 to 0.1 mm; the total cross-sectional height of the antenna is 0.95 to 1.1 mm.

4. The mobile phone back cover antenna according to claim 1, wherein: The dielectric materials of the first dielectric layer (2) and the second dielectric layer (5) have a dielectric constant of ε3 = 3.55; the thicknesses are H1 and H3 respectively, where H1 is 0.5 to 0.55 mm and H3 is 0.4 to 0.45 mm.

5. The mobile phone back cover antenna according to claim 1, characterized in that: The coplanar waveguide transmission line (11) is used to connect the artificial surface plasmon transmission line (13) with a single-conductor structure to the coaxial transmission line with a double-conductor structure in the microwave anechoic chamber, so as to realize the excitation and testing of the antenna object; the length of the coplanar waveguide transmission line (11) is not less than 4 mm, the width of the center conductor strip is 1.5 mm, and the distances between the center conductor strip and the ground planes on both sides thereof are both 0.1 mm.

6. The mobile phone back cover antenna according to claim 1, wherein: The transition structure (12) is used to achieve impedance matching between the coplanar waveguide transmission line (11) and the artificial surface plasmon transmission line (13); the distances between the ground planes on both sides and the center conductor strip gradually increase, and the depth of the groove on the center conductor strip gradually becomes deeper; the length of this transition structure is not less than 17.5 mm, and the width of the widest part of the ground plane is 10 mm.

7. The mobile phone back cover antenna according to claim 6, characterized in that: The length of the groove is 1.5 mm, the deepest depth is 0.8 mm, and the length and depth of the groove are used to determine the operating frequency band of the artificial surface plasmon transmission line (13).

8. The mobile phone back cover antenna according to claim 1, characterized in that: The artificial surface plasmon transmission line (13) is composed of not less than 27 H-shaped artificial surface plasmon units; the first circular metal patch (14) and the second circular metal patch (15) change the impedance of the artificial surface plasmon transmission line (13) through electrical coupling with the transmission line to form a leaky wave antenna.

9. The mobile phone back cover antenna according to claim 8, characterized in that: The length of the artificial surface plasmon transmission line (13) is not less than 67.5 mm; the length of the H-shaped artificial surface plasmon unit is not less than 2.5 mm and the width is not less than 3.5 mm.

10. The mobile phone back cover antenna according to claim 1, wherein: The first circular metal patch (14) and the second circular metal patch (15) located on both sides of the artificial surface plasmon transmission line (13), their diameters are determined by 1 / 4 wavelength corresponding to the center point of the operating frequency band of this transmission line; and the center distance between two adjacent circular metal patches on the same side is not greater than 5.5 mm, and the center distance between adjacent patches on both sides is not greater than 10 mm.

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