Polarization converter with stealth performance

Abstract

The utility model belongs to the technical field of polarization conversion, and relates to a polarization converter with stealth performance, the polarization converter is of a three-layer sandwich structure which sequentially comprises a butterfly-shaped resonator, a dielectric substrate and a metal substrate from top to bottom, the butterfly-shaped resonator and the metal substrate both use copper with the thickness of 0.017 mm as metal materials, and the dielectric substrate and the metal substrate are made of metal materials. The dielectric substrate isolates the butterfly-shaped resonator from the metal substrate, the dielectric substrate is filled with polytetrafluoroethylene, efficient dual-band linear-linear and dual-band linear-circular polarization conversion can be achieved, the frequency band utilization rate is improved, and at least 10 dB RCS reduction is achieved within the dual-band cross polarization frequency range.

Description

TECHNICAL FIELD

[0001] The utility model belongs to polarization conversion technical field relates to a polarization converter with stealth performance. BACKGROUND

[0002] Polarization is one of the important characteristics of electromagnetic waves, and controlling the propagation of electromagnetic waves to achieve various polarization modes has a significant impact on improving the utilization rate of frequency bands. The traditional way is to use natural materials to make devices with refraction, diffraction and absorption characteristics, which often faces a series of problems such as high cost, high energy consumption, limited bandwidth and complex production. With the emergence of metamaterials, it has electromagnetic properties that natural materials do not have: negative magnetic permeability and negative permittivity, making it a rising star in polarization conversion research. As a typical ultra-thin two-dimensional planar structure, metamaterials have the characteristics of miniaturization and high efficiency. By finding the best periodic arrangement of sub-wavelength units at a specific frequency, the phase and amplitude can be efficiently controlled to meet different ways of electromagnetic wave regulation such as linear-linear polarization, linear-circular polarization, and circular-circular polarization. Metamaterials are applied in imaging, absorbers, lenses, and stealth.

[0003] In the field of electromagnetic stealth, using metasurfaces to reduce RCS is an indispensable prerequisite for avoiding radar detection. The essence of RCS reduction is to change the way the object interacts with electromagnetic waves, improve the absorption of electromagnetic waves by the target body, and reduce the strength of the return signal. Compared with traditional methods such as multi-layer structure and loading lumped elements, using metasurfaces to achieve electromagnetic stealth avoids the complexity of design and large size. However, the existing metasurfaces have low frequency band utilization and single polarization mode, which cannot meet the diverse needs. UTILITY MODEL CONTENT

[0004] The utility model aims to overcome the defects of the prior art, and improve the utilization rate of frequency bands and the diversity of polarization modes. A polarization converter with stealth performance is designed to achieve efficient linear-linear and double-band linear-circular polarization conversion, improve the utilization rate of frequency bands, and achieve at least 10dB of RCS reduction in the cross-polarization frequency range of double-band.

[0005] To achieve the above purpose, the polarization converter of the utility model is a three-layer sandwich structure, consisting of a "butterfly-shaped" resonator, a dielectric substrate and a metal substrate from top to bottom. The "butterfly-shaped" resonator and the metal substrate both use copper with a thickness of 0.017mm as the metal material, and the electrical conductivity is 5.8x10 7S / m, the dielectric substrate is filled with polytetrafluoroethylene, the relative dielectric constant is 2.1, the loss tangent is 0.0002, and the thickness is 1.6 mm; the "butterfly-shaped" resonator is a symmetric structure, the symmetry axis is an inclined rectangular unit, the rectangular unit is 45° with the horizontal direction and coincides with the coordinate origin.

[0006] Compared with the prior art, the utility model has the following beneficial effects: the "butterfly-shaped" metasurface can produce multiple plasmonic resonances, realize cross-polarization conversion in the frequency range of 14.57-16.30GHz and 25.70-37.03GHz, the relative bandwidths are 11% and 36% respectively, and the conversion efficiency is more than 90%; realize left-handed circularly polarized waves and right-handed circularly polarized waves below 3dB in the frequency range of 17.78-25.31GHz and 37.38-37.73GHz, the relative bandwidths are 35% and 0.9% respectively; meanwhile, PTFE with low dielectric constant and low loss is used as the dielectric substrate, the "butterfly-shaped" resonator is rotated counterclockwise by 90° to form a mirror cell, the "butterfly-shaped" resonator itself and the mirror cell have equal amplitudes and the difference value of the co-polarization coefficient phase difference is 0, the difference value of the cross-polarization coefficient phase difference is 180°±37°, the interference effect of the incident electromagnetic wave on the metasurface is offset based on the phase cancellation principle to realize RCS reduction, and it is found through simulation experiments that the polarization converter is configured in a triangular chessboard mode that RCS reduction of at least 10dB is realized in the frequency range of 14-15.17GHz, 24.60-35.20GHz and 36.30-38GHz, and the relative bandwidths are 8.1%, 35.5% and 4.5% respectively. BRIEF DESCRIPTION OF DRAWINGS

[0007] Figure 1 The utility model provides the structure diagram of polarization converter.

[0008] Figure 2 The simulation condition of the utility model embodiment 1.

[0009] Figure 3 The polarization conversion principle diagram of the polarization converter.

[0010] Figure 4 The simulation experiment result picture of the utility model embodiment 3, wherein (a) is the reflection coefficient under normal incidence of y polarized wave, (b) is the change curve diagram of (c) is the PCR change curve diagram, (d) is the change curve diagram of AR value and e value.

[0011] Figure 5The diagram shows the structure of the "butterfly" resonator and mirror unit described in Embodiment 2 of this utility model (a), the reflection coefficients of the "butterfly" resonator "1" and the mirror unit "0", and the phase difference between the "butterfly" resonator "1" and the mirror unit "0" (c).

[0012] Figure 6 This is a schematic diagram of a triangular array model composed of the "butterfly" resonator rotated by 0°, 90°, 180° and 270° as described in Embodiment 2 of this utility model.

[0013] Figure 7 The diagram shows the PCR (a) and RCS reduction (b) of the "butterfly" resonator and mirror unit in Embodiment 2 of this utility model.

[0014] Figure 8 Figure (a) shows the simulation and measured results of the reflection coefficient and the RCS of Embodiment 4 of this utility model. Detailed Implementation

[0015] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0016] Example 1:

[0017] like Figure 1 As shown, the polarization converter provided in this embodiment has a three-layer sandwich structure, consisting of a "butterfly" resonator 1, a dielectric substrate 2, and a metal substrate 3 from top to bottom. Both the "butterfly" resonator 1 and the metal substrate 3 use copper with a thickness of 0.017 mm as the metal material, and the conductivity is 5.8 × 10⁻⁶. 7 S / m, dielectric substrate 2 isolates the "butterfly" resonator 1 from the metal substrate 3. Dielectric substrate 2 is filled with polytetrafluoroethylene, with a relative permittivity ε. r =2.1, loss tangent tanδ = 0.0002, thickness h = 1.6mm, the "butterfly" resonator 1 has a symmetrical structure, the axis of symmetry is an inclined rectangular unit, the rectangular unit makes an angle of 45° with the horizontal direction and coincides with the origin of the coordinate system; the size of the polarization converter is optimized in the simulation software CST, the simulation conditions are as follows. Figure 2 As shown, the parameters of the optimized unit are: p = 6mm, w = 0.28mm, l = 0.44mm, d = 1.5mm, r = 2.76mm, a = 1.39mm, c = 0.25mm, e = 1.64mm, b = 2.21mm.

[0018] The specific process by which the polarization converter in this embodiment achieves the conversion is as follows:

[0019] The electromagnetic wave incident along the y-axis is decomposed into two components U-V which are orthogonal to each other, where the U-axis and the V-axis are obtained by rotating the x-axis and the y-axis by 45°, respectively, and the polarization conversion principle is shown in Figure 6 By decomposition, the incident wave E i and the reflected wave E r are expressed as: where r u and r v are the reflection coefficients along the u-axis and the v-axis, and are the unit vectors on the u-axis and the v-axis, and in the u-v coordinate system, the co-polarization reflection coefficients are defined as R uu = E ru / E iu and R vv = E rv / E iv , respectively, and the cross-polarization reflection coefficients are defined as R uv = E ru / E rv and R vu = E rv / E ru , respectively, the co-polarization phases are and , and the phase difference is According to the polarization conversion principle, under the condition that and , when the phase difference satisfies , cross-polarization is achieved; when the phase difference is , circular polarization conversion is achieved, and when , the reflected wave is converted into a right-hand circularly polarized wave, , the reflected wave is converted into a left-hand circularly polarized wave; in the u-v coordinate system, in the frequency range of 14.57-16.30 GHz and 25.70-37.03 GHz, the phase difference achieves cross-polarization; in the frequency range of 17.78-25.31 GHz, the phase difference achieves cross-polarization; in the frequency range of 37.78-37.73 GHz, the phase difference achieves cross-polarization;

[0020] When the electromagnetic wave is vertically incident along the z-axis on the "butterfly-shaped" resonator 1, the relationship between the electric field components of the incident wave and the reflected wave on the x-axis and the y-axis is represented by the Jones matrix as follows: where and are the electric field intensity vectors of the reflected wave on the x-axis and the y-axis, respectively; and Ei and Er represent the electric field intensity vectors of the incident wave on the x-axis and y-axis respectively; i and r represent the incident and reflected respectively, co-polarization reflection coefficient and R xx , R yy represent the x-to-x reflection, y-to-y reflection respectively, cross-polarization reflection coefficient and R xy , R yx represent the x-to-y reflection, y-to-x reflection respectively, according to the reflection coefficient, the PCR for the y-polarized incident wave is represented as: At the same time, under the condition of y-polarized wave incidence, the co-polarization and cross-polarization reflection amplitudes and phase difference of the circularly polarized reflected wave should satisfy |R xx | = |R yy |, and the phase difference should satisfy k is an integer, where and are the phases corresponding to the co-polarization coefficient and cross-polarization coefficient respectively.

[0021] The axial ratio is used to evaluate the conversion efficiency of the circularly polarized reflected wave in this embodiment, and the axial ratio is where ζ is represented as The Stokes parameters are used to evaluate the conversion performance of the circularly polarized reflected wave, and the parameters I, Q, U and V are introduced, under the condition of y-polarized incident wave, I, Q, U and V are represented as: I = |R yy | 2 + |R xy | 2 , Q = |R yy | 2 - |R xy | 2 , The ellipticity of the circularly polarized conversion performance is e = V / I, where The value of e changes between -1 and 1, when |R xy | = |R yy | and , the ellipticity value e is -1, and the reflected wave is converted into a left-handed circularly polarized wave; when , the ellipticity value e is 1, and the reflected wave is converted into a right-handed circularly polarized wave; the relative bandwidth is the ratio of the signal bandwidth to the center frequency, that is: FBW = (f h - f l ) / f0 x 100, where f h , f l are the upper and lower limit frequencies of the effective bandwidth, and f0 is the center frequency.

[0022] Example 2:

[0023] The embodiment tests the stealth effect of the polarization converter described in embodiment 1. When the "butterfly" resonator itself and its mirror unit are under the same electromagnetic wave incidence, the reflection amplitudes of co-polarization and cross-polarization correspond to equal phase differences, and the phase difference of the cross-polarization reflection coefficient is within ±180°±36°, the phase difference of the co-polarization reflection coefficient is 0°, and the prerequisite for RCS reduction is met, as shown in Figure 5 , where "butterfly" resonator 1 is "1", the mirror unit is "0", the reflection amplitudes are A1 and A0 respectively, and the co-polarization phase and cross-polarization phase of the "butterfly" resonator and its mirror unit are and The co-polarization and cross-polarization reflection coefficients are R yy and R xy , which correspond to: At the same time, the reflection electric field of each unit in the array is quantified as:

[0024]

[0025] From Figure 5 (b) and 5(c), it can be seen that under y-polarized electromagnetic wave incidence, the co-polarization and cross-polarization reflection amplitudes of "butterfly" resonator "1" and mirror unit "0" are basically equal, and at the same time, the phase difference of the co-polarization reflection coefficient of the "butterfly" resonator and the mirror unit is 0°, and the phase difference of the cross-polarization reflection coefficient is ±180°.

[0026] In this embodiment, the "butterfly" resonator is arranged in a triangular arrangement, and the array is composed of 26×26 units. In the CST microwave studio, the array is simulated and analyzed in the time domain, and the "butterfly" resonator is arranged in a clockwise and 90° step rotation. When a beam of electromagnetic waves is vertically incident, due to the conservation of energy, the reflected energy is scattered to four different directions in the normal direction, thereby reducing the energy concentrated in a single direction. The triangular array model is shown in Figure 6 , after special arrangement, the RCS reduction performance can be quantified by the formula: Under the same scale of PEC, the chessboard corresponding to the RCS reduction of the triangular array model can be approximated as:

[0027]

[0028] It can be seen that the RCS reduction of 10dB of the triangular array is closely related to the PCR of the "butterfly" resonator, and when the cross-polarization amplitude is close to 0 and the co-polarization amplitude is as high as possible above -10dB, a higher cross-polarization conversion efficiency will be obtained in the corresponding frequency range, thereby assisting in the RCS reduction of at least 10dB, Figure 7 (a) and (b) are the PCR of the "butterfly" resonator and the mirror unit and the RCS reduction of the triangular array, respectively. It can be seen from the figure that: 1. The PCR of the "butterfly" resonator and the mirror unit is basically the same, and a conversion efficiency of more than 90% is obtained in the frequency range of 14.57-16.30GHz and 25.70-37.03GHz; 2. The arrangement of the triangular array makes the "butterfly" resonator obtain an RCS reduction of more than 10dB in the frequency range of 14-15.17GHz, 24.60-35.20GHz and 36.30-38GHz, and the relative bandwidths are 8.1%, 35.5% and 4.6%, respectively, and the maximum reduction peak is 25dB. At the same time, the arrangement of the triangular array makes the units mutually coupled, which is the reason why the "butterfly" resonator produces an RCS reduction of more than 10dB in the frequency band with a PCR lower than 90%.

[0029] Example 3:

[0030] This example simulates the polarization converter described in Example 1 under the precondition of frequency domain solution. As shown in Figure 2 , the "butterfly" resonator 1 is set with a floquet port boundary condition and simulated in the frequency range of 14-38GHz. At the same time, in order to evaluate the efficiency of the "butterfly" resonator in realizing cross-polarization conversion and circular polarization conversion, the PCR, AR and e are simulated, and the simulation results are shown in Figure 4 .

[0031] As shown in Figure 4 (a), under the incidence of y-polarized wave, in the frequency range of 14.57-16.30GHz and 25.70-37.03GHz, the cross-polarization coefficient R xy is close to 0, and the co-polarization coefficient R yy is lower than -10dB. In the frequency range of 17.78-25.31GHz and 37.38-37.73GHz, the co-polarization coefficient R yy and the cross-polarization coefficient R xy are approximately equal. At the resonance points of 15.33GHz, 26.15GHz, 27.36GHz and 33.73GHz, the co-polarization system R yy has peak values of -50dB, -43dB, -51dB and -60dB, respectively.

[0032] As shown in Figure 4(b) the phase difference between co-polarization and cross-polarization shown in Fig. 2 While in the frequency range of 37.38-37.73 GHz, the phase difference is This provides the condition for evaluating the performance of circular polarization conversion from the phase;

[0033] As Figure 4 (c) shown in Fig. 3, cross-polarization conversion occurs in the frequency ranges of 14.57-16.30 GHz and 25.70-37.03 GHz, with relative bandwidths of 11% and 36% respectively, and the conversion efficiency PCR is higher than 90%, and in the frequency ranges of 14.96-15.78 GHz and 25.92-36.64 GHz, the PCR value is higher than 97%, and at the resonance points of 15.33 GHz, 26.15 GHz, 27.36 GHz and 33.73 GHz, the conversion efficiency is close to 100%, and due to the symmetric characteristics of the designed "butterfly" resonator 1, similar results can be obtained under x-polarized wave incidence;

[0034] As Figure 4 (d) shown in Fig. 4, AR is lower than 3 dB in the frequency ranges of 17.78-25.31 GHz and 37.38-37.73 GHz, indicating that linear-to-circular polarization conversion is achieved, with relative bandwidths of 35% and 0.9% respectively, and at the same time, in the frequency range of 17.78-25.31 GHz, the ellipticity value e is close to -1, at which time the reflected wave is converted into left-hand circularly polarized wave, while in the frequency range of 37.38-37.73 GHz, the ellipticity value e is close to +1, at which time the reflected wave is converted into right-hand circularly polarized wave.

[0035] Example 4:

[0036] In this embodiment, the polarization converter described in Example 1 is made into a physical sample, the top layer of which is a "butterfly" resonator 1 printed with copper and with a thickness of 0.017 mm, the dielectric substrate is polytetrafluoroethylene (PTFE) with a thickness of 1.6 mm, and the back is covered with 0.017 mm copper, the sample is composed of 26x26 units, with a total size of 156x156 mm 2, all tests are carried out in a microwave darkroom, three groups of two identical horn antennas (horizontally placed as transmitting antennas, vertically placed as receiving antennas) with model numbers HB-0118-SMAF, HB-SGA-42-25 and HB-SGA-28-25 and frequency ranges containing wideband 1-18GHz, 18-26.5GHz and 26.5GHz-40GHz are fixed on a scanning frame and connected to a vector network analyzer with model number D N5225A through coaxial cables respectively, for test accuracy, the sample is placed in front of the antenna and the center of the sample is ensured to be at the same height as the horn antenna, during measurement, first, the same size calibration plate is used for normalization, then the signals are collected when the two horn antennas are kept horizontally (HH), and the collected signals are processed by the vector network analyzer to obtain the test data of co-polarization reflection coefficient; for cross-polarization reflection coefficient test, the transmitting antenna is kept horizontal, and the receiving antenna is rotated 90° and placed vertically (HV) to collect cross-polarization measurement data, Figure 8 (a) and (b) are respectively the simulation and measurement results of the "butterfly" resonator reflection coefficient and RCS, according to the results, it can be found that the general trend of the measurement results and the simulation results has good consistency, which shows the effectiveness of the proposed model; the measured results have obvious deviation around the resonance point, and the reasons for the deviation are that one aspect is the error of physical production and processing, and the other aspect is the error caused by the calibration error between the horn antenna and the sample.

[0037] The polarization converter provided by the utility model can realize cross-polarization conversion higher than 90% in the frequency range of 14.57-16.30GHz and 25.70-37.03GHz of ku band and ka band respectively, and simultaneously generate left-hand circularly polarized waves and right-hand circularly polarized waves in the frequency range of 17.78-25.31GHz and 37.38-37.73GHz of ku band and ka band respectively. Using the phase cancellation principle, the units are rotated by 90°, 180° and 270° in turn for triangular chessboard arrangement, at least 10dB RCS reduction is realized in the frequency range of 14-15.17GHz, 24.60-35.20GHz and 36.30-38GHz, the designed polarization converter not only has the advantages of high efficiency, low profile, novel dielectric substrate material, etc., but also can adapt to a 60° oblique incidence angle, and based on simulation and experimental verification, the effectiveness of the proposed design is ensured, and a new idea is provided for improving the utilization rate of Ku-ka band frequency.

Claims

1. A polarizer having stealth properties, characterized in that, The polarization converter is a three-layer sandwich structure, from top to bottom in turn "butterfly-shaped" resonator, dielectric substrate and metal substrate, "butterfly-shaped" resonator and metal substrate both use copper with thickness of 0.017mm as metal material, conductivity is 5.8×10 7 S / m, dielectric substrate separates "butterfly-shaped" resonator from metal substrate, dielectric substrate uses polytetrafluoroethylene to fill, relative dielectric constant is 2.1, loss tangent value is 0.0002, thickness is 1.6mm, "butterfly-shaped" resonator is symmetrical structure, symmetry axis is inclined rectangular unit, the angle between rectangular unit and horizontal direction is 45° and coincides with coordinate origin.

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