A method for improving the efficiency of planar EM electromagnetic lens array

Abstract

The present invention discloses a method for improving the efficiency of a planar EM electromagnetic lens array, which is applied to the field of spatial beamforming transmission and reception, and aims to solve the problem of low receiving peak power in the existing planar electromagnetic lens array. The present invention provides a design of a dual-mode microstrip circular patch antenna, which is surrounded by a short annular ring and can simultaneously excite side-firing and monopole radiation patterns. The method of the present invention adopts a dual-mode antenna unit, and achieves an adjustable radiation pattern by mixing side-firing and monopole radiation patterns; and realizes the effect of enhancing the power peak at different incident angles.

Description

Technical Field

[0001] The invention belongs to the field of spatial beamforming transmission and reception, and in particular relates to a planar EM lens. Background Art

[0002] A planar EM lens is a flat and thin structure that integrates several small-sized units designed to introduce different phase delays to the impinging electromagnetic waves. When the synthetic phase delay profile focuses the electromagnetic wave energy to a specific focal length, and an antenna array is placed at the focal length to receive the focused electromagnetic wave energy, a planar electromagnetic lens array is realized, which can be used for transmitting and receiving applications such as spatial beamforming.

[0003] Prior art 1 "C.Xue, J.Sun, X.Gao, F.Chen, Z.Pang, Q., ZN Chen, "An Ultrathin, Low-Profile and High-Efficiency Metalens Antenna Based on Chain Huygens'Metasurface," IEEE Trans.Antennas Propag., vol.70, no.12, pp.11442-11453, Sep.2022." proposed a Huygens element unit to synthesize the phase delay profile of the planar EM lens, and adopted a single horn antenna excitation to achieve high gain performance facing the side beam.

[0004] Prior art 2 "M. Jiang, Z. N. Chen, Y. Zhang, W. Hong, X. Xuan, "Metamaterial-based thin planar lens antenna for spatial beamforming and multibeam massive MIMO," IEEE Trans. Antennas Propag., vol. 65, no. 2, pp. 464-472, Feb. 2017." An antenna array is introduced at the focal length to realize a spatial beamformer, that is, different beam directions are achieved by individually exciting different antenna units. In addition, the numerical calculation results of the EM lens show that as the angle of the transmitted beam increases, the peak power decreases, which reduces the efficiency of the planar lens array.

[0005] Prior art 3 “Y. Zeng and R. Zhang, “Millimeter wave MIMO with lens antenna array: A new path division paradigm.” IEEE Trans. Com., vol. 64, no. 4, Apr. 2016.” Using a curved antenna array, the antenna units always receive energy focused by the EM lens at a narrow side-beam angle distribution.

[0006] Since the angular distribution caused by the focusing of the electromagnetic lens does not always conform well to the commonly used side-fire cosine-like radiation pattern, the prior art has the problem of low received peak power. Summary of the invention

[0007] In order to solve the above technical problems, the present invention proposes a method for improving the efficiency of a planar EM electromagnetic lens array.

[0008] The technical solution adopted by the present invention is: a method for improving the efficiency of a planar EM electromagnetic lens array, based on a planar EM lens array structure, comprising an EM lens 1 and a linear antenna array 2; the linear antenna array 2 is placed at a focal length F of the planar EM lens 1 and aligned with the y-axis;

[0009] The linear antenna array comprises a number of antenna units with equal spacing, and the structure of each antenna unit comprises four layers from top to bottom, which are respectively recorded as the first dielectric plate, the second dielectric plate, the third dielectric plate, and the fourth dielectric plate: a microstrip circular patch antenna is arranged on the first dielectric plate, and a short ring patch antenna surrounds the microstrip circular patch antenna, and the microstrip circular patch antenna and the short ring patch antenna are respectively connected to a coplanar waveguide transmission line arranged on the fourth dielectric plate through a copper probe passing through the four layers for feeding; the microstrip circular patch antenna radiates a basic side-fire pattern, and the short ring patch antenna radiates a high-order monopole pattern; the second dielectric plate is a ground plane, and the third dielectric plate is an adhesive layer;

[0010] The method specifically comprises:

[0011] The planar EM lens 1 focuses the TEM plane wave impinging energy onto the focal length of the EM lens;

[0012] The linear antenna array 2, placed at the focal length F of the planar EM lens 1 and aligned with the y-axis, controls the radiation direction of each antenna element through weighted broadside and monopole antenna patterns.

[0013] Beneficial effects of the present invention: The planar EM lens proposed in the present invention includes a large number of sub-wavelength phase delay units, which can be designed to synthesize a specific phase delay profile, and focus the impinging electromagnetic field on the surface of the EM lens to a specific part of the antenna array according to the incident angle of the electromagnetic field. Since the angular distribution caused by the focusing of the electromagnetic lens does not always conform well to the commonly used side-firing cosine-like radiation pattern, the present invention uses an adjustable radiation pattern synthesized by a hybrid side-firing and monopole pattern to improve the received peak power at different antenna array positions; its main radiation direction can be controlled by appropriately weighting the side-firing and monopole antenna patterns; thereby, the EM lens focusing angle distribution at different antenna positions can be better fitted, and the received power of each antenna unit at different incident angles can be improved; by controlling each antenna unit and the mode weighting factor, the received power is maximized, thereby generating a non-uniform antenna array; the method of the present invention is suitable for different application scenarios of transmitting and receiving planar electromagnetic lens arrays. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a planar EM lens array, in which the sub-wavelength EM lens units are highlighted;

[0015] Figure 2 The electric field magnitude and received power at the focal length of the assumed ideal antenna radiation pattern are given;

[0016] Where, (a) is the electric field amplitude, (b) is the power;

[0017] Figure 3 The electric field magnitude and received power at the focal length are given;

[0018] Where, (a) is the electric field amplitude, (b) is the power;

[0019] Figure 4 according to Figure 3 The results show the reduction of the peak received power under different incident angles.

[0020] Figure 5 is based on Figure 3 Schematic diagram of the focusing angle distribution of the EM lens at different incident angles at the peak power position;

[0021] Figure 6 It is a dual-mode antenna unit structure;

[0022] Figure 7 Given Figure 6 Simulated gain diagram of the antenna unit under different side-fire-monopole diagram weighting factors;

[0023] Figure 8 When the focal length is equal to the size of the EM lens, use Figure 7The radiation diagram in Figure 2 shows the peak enhancement effect of received power at different incident angles.

[0024] Fig. 9 When the focal length is half the size of the EM lens, Figure 7 The radiation diagram in Figure 2 shows the received power peak enhancement effect at different incident angles. DETAILED DESCRIPTION

[0025] A planar EM lens array structure of the present invention comprises a thin and flat EM lens and a linear antenna array.

[0026] Implementations described herein involve using periodic subwavelength unit structures in one or more layer configurations to realize a planar EM lens that synthesizes a focusing phase delay profile to focus the EM lens impact energy to the EM lens focal length.

[0027] According to one aspect of the present invention, an EM lens antenna array is implemented by an antenna unit that can steer the radiation pattern to a different primary direction relative to a conventional side-firing cosine-like microstrip patch pattern.

[0028] In a possible implementation, the steerable antenna is a microstrip circular patch antenna, which is surrounded by a short loop antenna, and the bottom of the short loop antenna is fed by a coplanar waveguide with a ground transmission line structure. The microstrip circular patch antenna radiates a basic side-fire pattern, while the short loop antenna radiates a higher-order monopole pattern.

[0029] Another aspect of the present invention is that the broadside and monopole antenna patterns are mixed together to produce a new radiation pattern whose primary radiation direction can be controlled by appropriately weighting the broadside and monopole antenna patterns. This mechanism can better fit the EM lens focusing angle distribution at different antenna positions and improve the received power of each antenna element at different incident angles. Each antenna element and pattern weighting factor can be controlled to maximize the received power, thereby producing a non-uniform antenna array.

[0030] These aspects, features and advantages of the present invention can be better understood through the following description and accompanying drawings. The accompanying drawings are integrated and constitute a part of this specification, show a form of embodiment of the present invention, and are related to the accompanying drawings. Figure 1 The present invention is intended to describe the principles of the present disclosure.

[0031] Assume a size of D lens ×D lensA square planar EM lens 1 with negligible thickness and a uniform linear antenna array (ULA) 2, the antenna array 2 includes M antenna elements 3 with a spacing of d. The antenna array 2 is parallel to the lens 1, placed at the focal length F of the planar EM lens 1, and aligned with the y-axis, as shown in FIG. Figure 1 As shown. When the TEM plane wave 4 (for simplicity, its electric field has only the x-axis component, that is, ) at a certain angle θ inc When 5 (depending on the y-axis) hits the planar EM lens 1, the electric field on the surface of the planar EM lens 1 can be written as

[0032]

[0033] in, represents the unit vector in the x direction;

[0034] A out / A inc is the attenuation coefficient of the EM lens, A out Represents the reflected electric field strength, A inc represents the incident electric field intensity; ψ(x,y)=k0ysinθ inc is the phase term that is different for each position on the lens and describes the phase delay due to the angle of incidence (k0 is the wave number), while Φ(x,y) is the phase delay provided by the EM lens and for a focusing EM lens its value is

[0035]

[0036] where x F ,y F , F is the focal length. According to the superposition principle, each infinitesimal part of the EM lens 1 will generate an electric field at any point in the space below the lens. Discrete the planar EM lens 1 into N×N d cell ×d cell The size of the cell is 6, such as Figure 1 As shown, the electric field at the focal length can be rewritten as:

[0037]

[0038] Where S 21 (x p ,y q ) is the (composite) characteristic of each EM lens unit, ∠S 21 (x p ,y q ) indicates S 21 (x p ,y q ), (x p,y q ) is the coordinate of the center position of the lens unit, and

[0039] Assuming that the planar EM lens 1 unit is small enough to be considered in the far field of the ULA unit (singular), and the presence of the ULA does not affect the performance of the planar EM lens unit, consider the ULA antenna unit 7, the power received by the mth ULA antenna unit can be approximated as

[0040]

[0041] where (i) each electric field contribution has been weighted by the radiation pattern of the ULA element, and (ii) the power density has been integrated over the antenna element surface; is the expression of the pattern function in the spherical coordinate system, where the direction is defined as the direction of the straight line from the center of the lens to each antenna position; Figure 2 Given θ inc =0, focus on (0,0,F), D lens =14.4λ, F=D lens / 2, the ideal plane electromagnetic lens |S 21 |=1,∠S 21 =Φ(x,y), with different θ inc The radiation pattern of an ideal antenna element excited by a plane wave and Figure 3 gives the same results, assuming the normalized path-like cosine diagram, but introducing the real microstrip patch antenna element diagram By comparison Figure 2 and Figure 3 , we can observe the electric field amplitude (|E ULA |) and power (P r ) decreases, and in both cases it can be seen that due to θ inc The increase in the electric field size and power reduction effect caused by the increase in Figure 4 It is shown that as the angle increases, the power reduction (calculated at the power peak position) is greater, which is due to θ pq For larger θ inc The angular distribution of is more concentrated at larger angles, such as Figure 5 shown.

[0042] Figure 2 , Figure 3 The abscissa λ represents the operating wavelength. Figure 4 Vertical coordinate P r,cos , P r,ideal They represent the received power of the cosine-like pattern and the ideal (omnidirectional) received power respectively.

[0043] In order to better handle this situation, the present invention proposes a dual radiation mode antenna. Figure 6 The antenna structure shown includes a microstrip circular patch antenna 8 with a radius of 2.2 mm and a short loop patch antenna 9 with an outer diameter of 4.62 mm. The radiation modes designed by the antenna structure include: a conventional microstrip patch side-fire radiation mode and a short loop monopole radiation mode with an operating frequency of 24.5 GHz.

[0044] A 0.13 mm×1.5 mm rectangular slot 10 opened on the surface of the microstrip circular patch antenna 8 can better adjust the working frequency of the antenna and reduce the radiation of high-order modes; the long side of the rectangular slot 10 is parallel to the x-axis;

[0045] A copper probe 11 with a radius of 0.1 mm is used to feed the microstrip circular patch antenna 8 through a coplanar waveguide 12 with a ground transmission line structure at the bottom of the substrate (the designed characteristic impedance is 50Ω, the distance between the transmission line and the ground at the same layer is 0.15 mm, and the transmission line width is 0.48 mm). The copper probe 11 passes through a circular small groove 13 with a radius of 0.15 mm opened on the middle ground plane 14. The ground plane 14 is made of copper.

[0046] There is a gap 15 with a width of 0.2 mm between the microstrip circular patch antenna 8 and the short loop patch antenna 9;

[0047] The inner radius of the annular patch is equivalently shortened by a copper via 16, and the annular patch is surrounded by a copper via 17 to reduce the propagation of surface waves. Another copper probe 18 is used to feed the short annular patch antenna 9 through another coplanar waveguide 19 with a ground transmission line structure at the bottom of the substrate.

[0048] Four 0.13 mm×4 mm rectangular slots 20 (at angles of ±45° and ±135° to the positive x-axis, respectively) and two 0.2 mm×1.5 mm horizontal slots 21 are cut on the short loop patch antenna 9 to improve the antenna mode purity.

[0049] At the bottom, two coplanar waveguides 12 and 19 are surrounded by copper through holes 22, and two open stubs 23 and 24 with a length of 3.4mm are used for impedance matching. Two 50Ω lumped ports 25 and 26 are used to feed the two antennas respectively. The antenna is designed on Rogers RT duroid 5880 with a thickness of 0.254mm, the transmission line is designed on RO4003C with a thickness of 0.254mm, and the bonding layer is RogersRO4450 with a thickness of 0.101mm.

[0050] By comparing them with the mode factor A 12 (and a 90 degree phase shift to account for the inherent phase delay of the two modes) is cleverly combined to give:

[0051]

[0052] in, represents the radiated electric field of the whole antenna, represents the radiated electric field of the side-firing mode, Represents the radiated electric field of the monopole mode.

[0053] Achieve different adjustable radiation patterns to improve the efficiency of the electromagnetic lens array, i.e. A 12 The value can be obtained through simulation. 12 The simulation gain (G) under the value is as follows Figure 7 As shown, in Figure 7 The adjustable radiation pattern can be observed in Figure 7 The radiation patterns in the figure are used to evaluate the performance of the EM lens array of the dual-mode antenna array, and different mode factors A are used to 12 The peak powers at different incident angles are compared. Figure 8 As shown in the figure, it can be seen how the hybrid transverse and monopole mode antenna element can better handle the Figure 5 The asymmetric EM lens angular distribution is shown. In contrast, using a pure monopole mode (A 12 =∞), which filters out the relevant part of the energy associated with narrow angles and is therefore unsuitable. Fig. 9 As shown in Figure 1, this effect is greater when the focal length is reduced because the angular distribution is wider. Finally, it should be emphasized that although the hybrid side-firing monopole radiation pattern antenna unit has a good power enhancement effect, the non-uniform antenna array is designed according to the EM lens angle distribution at each antenna array position, and the most appropriate hybrid side-firing monopole radiation pattern factor A is selected. 12 , which can further improve the peak power performance. In fact, if Figure 8 and Fig. 9 As shown, the best peak power performance at different incident angles is not always obtained by the same A 12 The mode factor is given.

[0054] A 12 It is the ratio of the contribution of the monopole mode to the side-fire mode to the radiation density, and can take values ​​of 1, 1.5, 2, to infinity, where infinity means that all the radiation is contributed by the monopole mode.

[0055] Figure 8 , 9 Vertical coordinate P r,multi-mode , P r,Tm11 They represent the received power under mixed mode excitation and the received power under single TM11 mode excitation (A12=0) respectively.

[0056] Those skilled in the art will appreciate that the embodiments described herein are intended to help readers understand the principles of the present invention, and should be understood that the scope of protection of the present invention is not limited to such specific statements and embodiments. For those skilled in the art, the present invention may have various changes and variations. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A method for improving the efficiency of a planar EM electromagnetic lens array, characterized in that: The electromagnetic lens array comprises: an EM lens (1) and a linear antenna array (2); The linear antenna array comprises a number of antenna units with equal spacing, and the structure of each antenna unit comprises four layers from top to bottom, which are respectively recorded as a first dielectric plate, a second dielectric plate, a third dielectric plate, and a fourth dielectric plate: a microstrip circular patch antenna is arranged on the first dielectric plate, a short ring patch antenna surrounds the microstrip circular patch antenna, and the microstrip circular patch antenna and the short ring patch antenna are respectively connected to a coplanar waveguide transmission line arranged on the fourth dielectric plate through a copper probe passing through the four layers for feeding; the microstrip circular patch antenna radiates a basic side-fire pattern, and the short ring patch antenna radiates a high-order monopole pattern; the second dielectric plate is a ground plane, and the third dielectric plate is an adhesive layer; a rectangular groove (10) is opened on the surface of the microstrip circular patch antenna; The method is specifically as follows: The planar EM lens (1) focuses the TEM plane wave impinging energy onto the focal length of the EM lens; A linear antenna array (2) is placed at a focal length F of a planar EM lens (1) and perpendicular to a rectangular slot (10), and controls the radiation direction of each antenna unit by weighted broadside and monopole antenna patterns, so as to maximize the received power of each antenna unit.

2. A method for improving the efficiency of a planar EM electromagnetic lens array according to claim 1, characterized in that: The calculation formula for the radiated electric field of a single antenna unit is: in, represents the radiated electric field of the whole antenna, represents the radiated electric field of the side-firing mode, represents the radiated electric field of the monopole mode, A 12 It is the ratio of the contribution of the monopole mode to the side-fire mode to the radiation density.

3. A method for improving the efficiency of a planar EM electromagnetic lens array according to claim 2, characterized in that: A 12 The adjustment is made according to the angle at which the TEM plane wave impinges on the planar EM lens (1).

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