Miniaturized axial-mode helical antenna based on artificial surface plasmons

Abstract

The invention discloses a miniaturized axial mode helical antenna based on artificial surface plasmon, comprising a plastic cylindrical support structure, a metal structure wound on the plastic cylinder and a metal floor at the lower layer. The metal structure comprises an artificial surface plasmon structure and a matching structure located below it. The artificial surface plasmon structure comprises 5 turns of artificial surface plasmon unit structure wound along the axial direction of the plastic cylinder, which is directly connected to the matching structure; the matching structure comprises a microstrip line structure for adjusting the input port impedance and a metal feeding probe. The invention reduces the length of the metal strip by 20%, while the physical aperture, height and volume are reduced by 36%, 20% and 49% respectively. The invention has good axial mode radiation performance and right-hand circular polarization (RHCP) characteristics, and also has the characteristics of high bandwidth and high gain, and is simple to process and low in cost, which helps to improve the system integration of wireless communication technology.

Description

Technical Field

[0001] The invention belongs to the field of helical antennas and artificial surface plasmons, and in particular relates to a miniaturized axial mode helical antenna based on artificial surface plasmons. Background Art

[0002] In the optical band, the resonant response of electromagnetic waves and free electrons on the metal surface is called surface plasmon. This mode can effectively transmit and localize light waves, has subwavelength characteristics, and has a wide range of applications in optical communication systems. In order to achieve this electromagnetic response in a lower frequency band, the concept of artificial surface plasmon was proposed. This mode can support and propagate electromagnetic waves very similar to surface plasmons in a lower frequency band. With the introduction of a two-dimensional planar surface plasmon waveguide structure that is both ultra-thin and flexible to support this mode, it is possible to design ultra-thin plasma devices, giving circuits based on artificial surface plasmon structures a new development prospect in the microwave and terahertz frequency bands.

[0003] Helical antennas have the advantages of small size, strong directivity, high gain, and easy implementation. Axial mode helical antennas are widely used in wireless communication systems such as satellites and radars because their circular polarization performance can be achieved in broadband and low axial ratio. In order to improve the integration of the system, researchers are increasingly inclined to the research and design of miniaturized antennas. Since the volume of the antenna is closely related to its operating wavelength, this means that some antenna performance (such as gain) will deteriorate due to the reduction in size, so it is difficult to achieve a balance between the size and performance of the helical antenna. According to existing research, miniaturized designs often use expensive media or complex circuit network designs. It can be seen from the dispersion curve of artificial surface plasmons that this mode has a high phase constant and a small equivalent wavelength, so that the artificial surface plasmon exhibits slow-wave characteristics, which can reduce the physical size of the structure. According to the prior art, the miniaturization design method of axial mode helical antennas based on artificial surface plasmon structures has not been reported. Summary of the invention

[0004] The purpose of the present invention is to provide a miniaturized axial mode helical antenna based on artificial surface plasmons, to achieve a miniaturized design of the helical antenna and at the same time ensure that the antenna has good gain and broadband characteristics.

[0005] The specific technical solutions of the present invention are as follows:

[0006] A miniaturized axial mode helical antenna based on artificial surface plasmon includes a plastic cylindrical support structure, a metal structure wound around the plastic cylindrical support structure and a metal floor at the bottom, wherein the metal structure includes an artificial surface plasmon structure and a matching structure at the bottom.

[0007] The artificial surface plasmon structure includes identical slotted artificial surface plasmon units, which are directly connected to the matching structure;

[0008] The matching structure includes a microstrip line structure for adjusting the input port impedance and a metal feed probe.

[0009] Furthermore, the slotted artificial surface plasmon units are evenly arranged and wound on the surface of the plastic cylindrical support structure, and the electric field is alternately vertical within a propagation wavelength, forming a circular polarization effect.

[0010] Furthermore, the slotted units are evenly arranged and wound on the surface of the plastic cylindrical support structure at a pitch angle of 13°, with a total of 5 turns.

[0011] Furthermore, the slot unit width is 5.2 mm, the slot width is 1.5 mm, and the slot depth is 4.2 mm.

[0012] Furthermore, the cross-sectional shape of the groove of the slotted artificial surface plasmon unit along the winding direction is rectangular, V-shaped or trapezoidal.

[0013] Furthermore, the effective wavelength supported by the artificial surface plasmon structure and the spiral circumference satisfy the following relationship:

[0014]

[0015] Among them, C is the spiral circumference, that is, the circumference of the plastic cylinder; λ is the effective wavelength supported by the artificial surface plasmon structure; using this relationship, at a certain frequency, the spiral circumference can be reduced by reducing the effective wavelength λ, thereby achieving a miniaturized design.

[0016] Furthermore, the material of the plastic cylinder is foam, and the dielectric constant ε γ =1.1.

[0017] The miniaturized axial mode helical antenna based on artificial surface plasmon of the present invention has the following advantages:

[0018] The spiral antenna of the present invention combines antenna theory with artificial surface plasmon theory, designs an artificial surface plasmon structure on the metal strip of the traditional microstrip spiral antenna, and realizes a subwavelength structure with a high phase constant by designing the slot depth of the slotted artificial surface plasmon unit, thereby effectively reducing the size of the antenna. Compared with the traditional microstrip spiral antenna, the spiral length, physical aperture, antenna height and total volume of the antenna are significantly reduced, and it shows good circular polarization radiation characteristics within the working frequency band; in addition, the present invention is simple to realize, has low manufacturing cost, is easy to process and has good circular polarization characteristics, and has important application prospects in the fields of radar and wireless communication systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic structural diagram of a miniaturized axial mode helical antenna based on artificial surface plasmons of the present invention;

[0020] Figure 2 It is a schematic diagram of the artificial surface plasmon structure of the present invention;

[0021] Figure 3 It is a schematic diagram of the matching structure of the present invention;

[0022] Figure 4 It is a schematic diagram of the structural dimensions of the slotted artificial surface plasmon unit of the present invention;

[0023] Figure 5 It is a dispersion curve diagram of the artificial surface plasmon unit and microstrip line of the present invention;

[0024] FIG6(a) is a schematic diagram showing the surface current distribution of the first coil of the axial mode helical antenna and its equivalent schematic diagram at time t=0 of the present invention;

[0025] FIG6( b ) is a schematic diagram showing the surface current distribution of the first turn of the axial mode helical antenna and its equivalent schematic diagram at time T / 4 of the present invention;

[0026] Figure 7 are the simulated and measured values ​​of the normalized two-dimensional far-field radiation pattern at 3.8 GHz of the present invention;

[0027] Figure 8 are the simulated and measured values ​​of the normalized two-dimensional far-field radiation pattern at 4.1 GHz of the present invention;

[0028] Fig. 9 The S of the present invention 11 Simulated and measured values ​​of parameters;

[0029] Fig.10 are the simulated and measured values ​​of the axial ratio (AR) and gain of the present invention;

[0030] Fig.11 It is a comparison diagram of the physical model of the present invention and the traditional helical antenna;

[0031] Fig.12 is the difference between the present invention and the conventional helical antenna 11 The measured value of the parameter;

[0032] Fig.13 It is the measured value of the axial ratio and gain of the present invention and the conventional helical antenna.

[0033] Explanation of the marks in the figure: 1. Artificial surface plasmon structure; 2. Matching structure; 11. Slotted artificial surface plasmon unit; 21. Microstrip line structure; 22. Metal feeding probe. DETAILED DESCRIPTION

[0034] In order to better understand the purpose, structure and function of the present invention, the miniaturized axial mode helical antenna based on artificial surface plasmon of the present invention is further described in detail below with reference to the accompanying drawings.

[0035] like Figure 1 As shown, the miniaturized helical antenna of the present invention comprises a plastic cylindrical support structure, a metal structure wound on the plastic cylindrical support structure and a metal floor at the bottom; the metal structure comprises an artificial surface plasmon structure 1 and a matching structure 2 at the bottom; the material of the plastic cylindrical support structure is foam, and the dielectric constant ε r =1.1, the antenna height is 60mm.

[0036] like Figure 2 As shown, the artificial surface plasmon structure 1 includes a plurality of slotted artificial surface plasmon units 11, and the cross-sectional shape along the axis direction thereof is rectangular, V-shaped or trapezoidal.

[0037] like Figure 3 As shown, the matching structure 2 is composed of a microstrip line structure 21 for adjusting the input port impedance and a metal feeding probe 22. The RF signal source is connected to the metal probe 22 to feed the antenna.

[0038] like Figure 4 As shown, in this example, the unit width, slot width, and slot depth of the slotted artificial surface plasmon unit 11 are the same, the unit width p is 5.2 mm, the slot width a is 1.5 mm, and the slot depth h is 4.2 mm.

[0039] According to antenna theory, the lobe pattern of an n-turn helical antenna can be considered as the lobe pattern of a single turn multiplied by the array factor lobe pattern of a linear array composed of n isotropic point sources. Its matrix factor E can be expressed as:

[0040]

[0041] Where ψ=S r cosφ+δ is the total phase difference between the fields from adjacent sources, where S r is the distance between array elements; φ is the angle between the antenna radiation direction and the horizontal plane; δ is the phase difference between adjacent elements. For a helical antenna, the distance between elements S r =2πS / λ 0 , where S is the antenna pitch, that is, the distance of each spiral turn in the vertical direction. Therefore, ψ can be expressed as

[0042]

[0043] Where p = v / c 0is the relative phase velocity of the wave propagating along the spiral conductor, v is the propagation phase velocity on the spiral conductor, c 0 is the speed of light in free space, λ 0 is the wavelength in free space, and L is the length of the helix. For the case of axial mode radiation, φ = 0 and ψ is an integer multiple of -2π, denoted as ψ = -2πm, where m is an integer greater than 0 (m = 1, 2, 3, ...). In general, m = 1, so the expression for the relative phase velocity p is:

[0044]

[0045] In the above formula, L 2 =π 2 D 2 +S 2 ; S = Ctanα is the antenna pitch, D = C / π is the antenna diameter, C is the antenna coil radius; α is the coil pitch angle. When 12°≤α≤14° and C≈λ 0 When , the antenna has the maximum bandwidth, and the relative phase velocity p can be approximated as:

[0046]

[0047] Using the formula p = v / c 0 and v = 2πf / k, we can get the spiral circumference (C) of antennas with different propagation constants at the same frequency. 1 , C 2 ) and its propagation constant (k 1 , k 2 ) can be written as

[0048]

[0049] From the above formula, we can see that the larger the value of the propagation constant k, the smaller the spiral radius C, which is the physical radius of the spiral antenna. The dispersion curve comparison of the microstrip line and the artificial surface plasmon unit is shown in the figure below: Figure 5 Compared with the microstrip line, the dispersion curve of the artificial surface plasmon unit shows obvious slow wave characteristics, that is, the propagation constant k is larger at the same frequency. x The increase of provides the possibility of realizing miniaturization design. In the present invention, an artificial surface plasmon structure is introduced, and its propagation constant is significantly greater than the propagation constant of the microstrip line structure within a certain frequency range, so the physical size of the antenna can be effectively reduced.

[0050] Taking the radiation at 4.0 GHz as an example, the propagation constant k of the artificial surface plasmon unit can be obtained from the dispersion curve: sspp =105.75m -1 , and then calculate λsspp =59.4mm. Considering the axial mode radiation condition 0.8≤C ssspp / λ sspp ≤1.2, C can be calculated ssspp The range is 47.5-59.4mm. In order to achieve the purpose of miniaturization design, C ssspp It should be as small as possible within this range. According to the relationship L 2 =π 2 D 2 +S 2 , when we choose α = 13° and C ssspp =50mm, the spiral distance S = 11.2mm and the diameter D = 15.1mm can be obtained. In addition, the metal floor is usually slightly larger than 3 / 4λ in diameter. 0 The circular metal plate is 70mm in this design. The final designed helical antenna consists of 5 turns with a total height of 60mm.

[0051] When transmitting the signal, the SMA connector of the RF signal source is directly connected to the matching structure. As shown in Figure 6 (a), the first circle surface current distribution of the antenna at t = 0 and its equivalent schematic diagram are shown, and the surface current vector points to the +x direction; Figure 6 (b) shows the first circle surface current distribution of the antenna at t = T / 4 and its equivalent schematic diagram, and the surface current vector points to the +y direction. It can be seen that after each quarter cycle, the direction of the electric field changes from +x to +y, the directions rotate 90° and are perpendicular to each other in the process, thus generating right-hand circularly polarized axial mode radiation.

[0052] Figure 7 and Figure 8 The simulation and measurement values ​​of the normalized two-dimensional far-field radiation pattern of the miniaturized axial mode helical antenna based on artificial surface plasmon at 3.8GHz and 4.1GHz in the xoz plane are shown respectively. It can be seen that the antenna has good right-hand circularly polarized axial mode radiation characteristics. In addition, the cross-polarization of the antenna is less than -15dB, which also shows that it has good circularly polarized radiation performance.

[0053] Fig. 9 The S of the miniaturized axial-mode helical antenna based on artificial surface plasmon is shown. 11 The results show that the simulated S 11 The parameters are lower than -10dB in the range of 3.4-4.8GHz, and the relative bandwidth is 34%; the measured results are in the range of 3.3-4.7GHz, and the relative bandwidth is 35%. Both the simulation results and the measured results show that the antenna is well matched near the center frequency and radiates efficiently.

[0054] Fig.10The simulation and measured values ​​of the axial ratio and gain of the miniaturized axial mode helical antenna based on artificial surface plasmon are shown. The results show that from 3.6GHz to 4.9GHz, the antenna axial ratio is less than 3dB, showing good circular polarization characteristics. In addition, the gain is greater than 9dB in the working band, with a maximum value of 9.6dB, indicating that the antenna has good axial mode radiation characteristics over a wide frequency range. It is worth noting that the measured gain is slightly lower than the simulated gain due to the loss and error in sample manufacturing and measurement, as well as the welding error of the coaxial connector.

[0055] Fig.11 The comparison diagram of the physical model of the miniaturized axial mode helical antenna based on artificial surface plasmon and the traditional helical antenna is shown. Both antennas are designed to use a 13° elevation angle at 4GHz and are composed of 5 turns of metal spiral coils. The main difference between the two is that the traditional antenna uses a microstrip structure. It can be clearly seen that the size of this antenna is smaller than that of the traditional helical antenna. The specific size parameters are compared in the following table (unit: mm):

[0056] Spiral radius Antenna height Pitch SSPPs 16 61.55 11.3 Traditional helical antenna 20 75.69 14.14

[0057] Fig.12 The S curves of the miniaturized axial mode helical antenna based on artificial surface plasmon and the traditional helical antenna in the same frequency band are shown. 11 The measured values ​​of the parameters. It can be seen that the S 11 The range from 3.3 GHz to 4.7 GHz is less than -10 dB, showing good matching characteristics and broadband characteristics.

[0058] Fig.13 The measured values ​​of the axial ratio and gain of the miniaturized axial mode helical antenna based on artificial surface plasmon and the traditional helical antenna are shown. It can be seen that both antennas achieve broadband circularly polarized radiation; the size of the traditional antenna is almost twice the size of this antenna, and the gain is only about 0.2-0.3dB higher than that of this antenna.

[0059] Compared with the traditional microstrip spiral antenna, the miniaturized axial mode spiral antenna based on artificial surface plasmon has significantly reduced spiral length, physical aperture, antenna height and total volume, with reductions of 20%, 36%, 20% and 49% respectively, and shows good circularly polarized radiation characteristics at 3.6-4.9GHz.

[0060] It should be emphasized that the above is only an example of the present invention at a selected frequency of 4 GHz. Any simple modifications, equivalent changes and modifications made to the above examples at different frequencies based on the technical essence of the present invention are within the scope of the technical solution of the present invention.

Claims

1. A compact axial mode helical antenna based on artificial surface plasmon, characterized in that: It comprises a plastic cylindrical support structure, a metal structure wrapped around the plastic cylindrical support structure and a metal floor at the bottom, wherein the metal structure comprises an artificial surface plasmon structure (1) and a matching structure (2) at the bottom; The artificial surface plasmon structure (1) comprises identical slotted artificial surface plasmon units (11) wound along the axial direction of a plastic cylinder and evenly arranged and wound on the surface of a plastic cylindrical support structure at a pitch angle of 13°, with a spiral pitch S of 11.2 mm, a spiral diameter D of 15.1 mm, a spiral circumference S of 50 mm, and a total of 5 turns. The structure is directly connected to a matching structure (2), and the electric field is alternately perpendicular in direction within a propagation wavelength, forming a right-hand circular polarization effect; The matching structure (2) comprises a microstrip line structure (21) for adjusting the input port impedance and a metal feeding probe (22).

2. The compact axial mode helical antenna based on artificial surface plasmon according to claim 1, characterized in that: The slotted artificial surface plasmon unit (11) has a width of 5.2 mm, a slot width of 1.5 mm, and a slot depth of 4.2 mm.

3. The compact axial mode helical antenna based on artificial surface plasmon according to claim 1, characterized in that: The cross-sectional shape of the groove of the grooved artificial surface plasmon unit (11) along the winding direction is rectangular, V-shaped or trapezoidal.

4. The compact axial mode helical antenna based on artificial surface plasmon according to claim 1, characterized in that: The effective wavelength supported by the artificial surface plasmon structure (1) and the helical circumference satisfy the following relationship: Wherein, C is the spiral circumference, i.e., the circumference of the plastic cylinder; λ is the effective wavelength supported by the artificial surface plasmon structure (1); by using this relationship, at a certain frequency, the spiral circumference can be reduced by reducing the effective wavelength λ, thereby achieving a miniaturized design.

5. The compact axial mode helical antenna based on artificial surface plasmon according to claim 1, characterized in that: The material of the plastic cylinder is foam, and the dielectric constant ε γ =1.1.

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