Method for obtaining electromagnetic scattering characteristics of cylindrical frequency selective surface

[0033] Specific implementation mode one, combination Figure 1 to Figure 5 In this embodiment, the method for obtaining electromagnetic scattering characteristics of a cylindrical frequency selective surface described in this embodiment is described. The method analyzes the electromagnetic scattering characteristics of the cylindrical frequency selective surface structure. The cylindrical frequency selective surface structure includes metal The plate 1 and the dielectric layer 3 with a thickness of dmm, the dielectric constant of the dielectric layer 3 is ε r , The magnetic permeability is 1; the surface of the metal plate 1 is engraved with through holes 2 in the shape of a rectangular grid. The through holes 2 are Y-shaped, and every two adjacent Y-shaped holes are along the cylindrical surface. The spacing is 40mm, the metal plate 1 is bent according to the radius of curvature of the cylindrical surface as P, and the dielectric layer 3 is attached to the inner side of the metal plate 1; d, ε r , P are positive numbers;

[0034] The specific process of this method is:

[0035] The electromagnetic simulation software based on the finite difference time domain algorithm is used to simulate and calculate the situation of the uniform plane wave vertically irradiated on the curved FSS structure in space, and obtain the S-parameter curve reflecting the electromagnetic transmission and reflection characteristics of the curved FSS. S21 represents the transmission coefficient of the electromagnetic wave;

[0036] When the cylindrical frequency is selected, the thickness of the dielectric layer 3 of the surface structure is d and the dielectric constant is ε r When the size of the Y-shaped hole structure and the Y-shaped hole structure remain unchanged, when the radius of curvature of the metal plate 1 is 160mm, 200mm, 300mm and 800mm;

[0037] The electromagnetic simulation software based on the finite-difference time-domain algorithm is used to irradiate the uniform plane wave in the space vertically to the dielectric layer 3 of the surface structure when the cylindrical frequency is selected. The thickness is d and the dielectric constant is ε r The dimensions of the Y-shaped hole structure and the Y-shaped hole structure remain unchanged. The surface of the cylindrical frequency when the radius of curvature of the metal plate 1 is 160mm, 200mm, 300mm, and 800mm is selected for simulation calculation, and 4 simulation curves are obtained.

[0038] Compare the curve of the surface structure transmission characteristic parameter with the cylindrical frequency with the radius of curvature of the metal plate 1 being 160mm, 200mm, 300mm and 800mm;

[0039] When the radius of curvature of the cylindrical metal plate 1 gradually changes from 160mm to a plane, as the radius of curvature of the metal plate 1 increases to 200mm, 300mm, and 800mm, the transmittance of the center frequency band increases and the transmission characteristic parameter curve becomes smooth. The out-of-band oscillation is significantly reduced, and the center frequency of resonance also shifts accordingly;

[0040] When the frequency selective surface structure changes from a plane to a cylindrical surface with a radius of curvature of 300mm, the center frequency shifts to low frequency; when the radius of curvature changes from 300mm to 160mm, the center frequency point shifts to high frequency;

[0041] Electromagnetic scattering characteristics of cylindrical frequency selective surface: When the frequency selective surface is gradually bent from a planar structure to a curved surface with large curvature, the irradiation of the planar electromagnetic wave on the frequency selective surface has become a multi-angle incidence, and the phase difference between the structural units A good coupling cannot be obtained, and multiple new scattering spectrums appear; the intensity of the reflected wave and the multiple-mode diffraction wave changes sharply at the same time, which causes the spectrum to oscillate and the frequency point drifts; and due to the curvature of the cylindrical surface, The surface scattering effect is sharply enhanced, and the transmittance of the center frequency band decreases;

[0042] When the thickness d of the dielectric layer 3, the dielectric constant ε r , The radius of curvature of the metal plate 1 and the arm width of the Y-shaped hole remain unchanged, the arm length L is increased from 12mm to 18mm, and the increase interval is 1mm:

[0043] The electromagnetic simulation software based on the finite difference time domain algorithm is used to irradiate the uniform plane wave in the space vertically to the thickness d and the dielectric constant ε of the dielectric layer 3. r , The radius of curvature of the metal plate 1 and the arm width of the Y-shaped hole remain unchanged, the arm length L is increased from 12mm to 18mm, and the cylindrical frequency selection surface when the interval is 1mm is increased for simulation calculation, and 7 simulation curves are obtained; Comparing the obtained 7 sets of S21 parameter curves, it is obtained that the center resonance frequency of the Y-shaped hole cylinder FSS shifts to low frequency as the Y-shaped hole arm length increases, and the transmittance of incident electromagnetic waves gradually increases;

[0044] Cylindrical frequency selection surface electromagnetic scattering characteristics: when the Y-shaped hole arm length increases, the metal coverage of the cylindrical FSS decreases, the duty cycle increases, the reflection ability of the incident electromagnetic wave is weakened, and the transmission ability increases; the center frequency moves toward the low frequency Offset, indicating that the center resonance frequency of the curved FSS is related to the size of the structural unit, and the center frequency decreases as the size of the structural unit increases;

[0045] When the dielectric constant ε r , The radius of curvature of the metal plate 1, the width of the arms of the Y-shaped hole and the width of the arms of the Y-shaped hole remain unchanged, and the thickness d of the dielectric layer is increased from 1mm to 5mm successively, when the increasing interval is 1mm:

[0046] The electromagnetic simulation software based on the finite-difference time-domain algorithm is used to irradiate the uniform plane wave in the space vertically to the dielectric constant ε r , The radius of curvature of the metal plate 1, the width of the arm of the Y-shaped hole and the width of the Y-shaped hole are all kept unchanged, the thickness d of the dielectric layer is increased from 1mm to 5mm in turn, and the cylindrical frequency is selected for the surface simulation calculation when the increasing interval is 1mm. , Obtain 5 simulation curves to compare the 5 simulation curves obtained, it is obtained that as the thickness of the dielectric layer increases, the center resonance frequency of the cylindrical FSS drifts to low frequency, and the speed of the center frequency drift gradually decreases, and the frequency reaches about At 3.1GHz, as the thickness increases, the speed of center frequency drift slows down;

[0047] Cylindrical frequency selection surface electromagnetic scattering characteristics: the thickness of the dielectric layer will only shift the center frequency at resonance without affecting the scattering ability of electromagnetic waves;

[0048] When the curvature radius of the metal plate 1, the arm width of the Y-shaped hole, the arm width of the Y-shaped hole and the thickness d of the dielectric layer remain unchanged, the dielectric constant ε r Take 2, 3, and 4: respectively:

[0049] The electromagnetic simulation software based on the finite difference time domain algorithm is used to irradiate the uniform plane wave in the space perpendicularly to the radius of curvature of the metal plate 1, the arm width of the Y-shaped hole, the arm width of the Y-shaped hole, and the thickness d of the dielectric layer remain unchanged. Dielectric constant ε r Take the cylindrical frequency selection surface at 2, 3, and 4 respectively for simulation calculation, obtain 3 simulation curves, and compare the obtained 3 simulation curves.

[0050] When the dielectric constant increases, the center frequency of the cylindrical FSS resonance shifts to low frequencies, while the shape of the S21 curve remains basically unchanged;

[0051] Cylindrical frequency selection surface electromagnetic scattering characteristics: The dielectric constant is within a range of values. As the dielectric constant increases, the resonant frequency of the curved FSS will shift to low frequencies, while the electromagnetic wave scattering ability remains unchanged.

[0052] The present invention uses electromagnetic simulation software based on finite difference time domain (FiniteDifferenceTimeDomain, FDTD) algorithm to simulate and calculate the situation that a uniform plane wave in space is vertically irradiated on a curved FSS structure, thereby obtaining an S parameter curve reflecting the electromagnetic transmission and reflection characteristics of the curved FSS , And further explore the electromagnetic scattering characteristics of curved FSS.

[0053] According to different applications of FSS, the structure shape of the curved FSS needs to be adjusted differently. In order to have generality, the present invention studies the influence of the curvature of the curved FSS, the size of the unit structure and the characteristics of the dielectric layer on its electromagnetic scattering characteristics.

[0054] The schematic diagram of the Y-shaped hole structure unit used; it consists of a size of 40×40mm 2 , A uniform dielectric layer with a thickness of 1mm is unilaterally loaded on a metal patch with a centrally polarized symmetrical Y-shaped hole in the center. The Y-shaped hole has an arm length of 16mm and an arm width of 4mm. The plane structure unit is arranged and expanded in the form of a rectangular grid on the plane to form a finite plane FSS, and then the structure is bent according to a cylinder with a radius of 160mm, and the final coverage area is 320×320mm. 2 , A cylindrical frequency selection surface with a radius of curvature of 160mm.

[0055] In order to explore the influence of the curvature of the curved surface FSS on the electromagnetic scattering characteristics, the Y-hole cylindrical FSS with the radius of curvature of 160mm, 200mm, 300mm, 800mm and the flat FSS with the same coverage area (that is, the curvature is infinite) are designed according to the above methods. , The comparison diagram of the Y-shaped hole cylindrical FSS structure with each radius of curvature is shown as image 3 Shown.

[0056] In order to further explore the electromagnetic scattering characteristics of the designed cylindrical FSS, the present invention adopts the following method: Taking a general case as an example, a plane TM wave is used to uniformly irradiate the top of the cylindrical FSS, such as figure 1 As shown, the S parameter is used to describe at the same time, that is, S21 represents the transmission coefficient of electromagnetic waves, and S11 measures the reflection of electromagnetic waves. According to this method, the Y-shaped hole cylindrical FSS structure with different curvature radius is simulated and calculated, and the transmission characteristic curve in each case is obtained as figure 2 Shown. From the comparison diagram of transmission characteristic parameters, it can be concluded that the transmission characteristic of cylindrical FSS varies with the radius of curvature. When the radius of curvature of the cylinder gradually changes from 160mm to a plane, as the radius of curvature increases (the curvature decreases), the transmittance of the center frequency band increases, the transmission characteristic parameter curve becomes smooth, and the out-of-band oscillation is significantly reduced. The center frequency of resonance also shifts accordingly. When the radius of curvature changes from a plane to 300mm, the center frequency shifts to low frequency, and when the radius of curvature changes from 300mm to 160mm, the center frequency shifts to high frequency.

[0057] It can be seen that when the FSS is gradually bent from a planar structure to a curved surface with large curvature, the radiation of plane electromagnetic waves has become a multi-angle incident problem in the case of FSS, and the phase difference between the structural units cannot be well coupled, so There have been many new scattering spectrums; the intensity of the reflected wave and the multiple-mode diffraction wave changes sharply at the same time, causing the spectrum to oscillate sharply and the frequency point is shifted; and because the cylindrical surface is curved, the surface scattering effect is sharply enhanced, and the center The frequency band transmission will decrease accordingly.

[0058] The size of the structural unit is the decisive factor for the central resonance frequency of the FSS. The resonant frequency of the planar FSS formed by the ring unit is approximately equal to the circumference of the ring structure. The size of the central connection unit resonates from the beginning to the end and the span is about λ/2. For curved FSS structures, the change in the size of the structural unit will affect the coupling between the units and play an important role in the electromagnetic scattering characteristics of the FSS. Therefore, changing the size of the cylindrical FSS unit will not only affect the change of the center resonance frequency. .

[0059] The present invention uses Y-shaped holes as the structural unit of the cylindrical FSS, and explores the law of influence of the size of the Y-shaped hole unit on the electromagnetic scattering characteristics of the cylindrical FSS. The arm width of the Y-shaped hole structure remains unchanged at 4mm, the arm length L is from 12mm to 18mm, and the interval is 1mm. The FSS of the cylindrical surface with a curvature radius of 200mm corresponding to these groups of arm lengths are simulated and calculated respectively, and the S21 parameters are obtained as image 3 Shown.

[0060] It can be seen from the curve that the center resonance frequency of the Y-hole cylindrical FSS shifts to low frequency with the increase of the Y-shaped hole arm length, and the transmittance of incident electromagnetic waves gradually increases. This is because when the Y-shaped hole arm length increases, the metal coverage of the cylindrical FSS decreases, the duty cycle increases, the reflection ability of the incident electromagnetic wave is weakened, and the transmission ability increases; the center frequency shifts to low frequency, indicating The center resonance frequency of the curved FSS is also related to the size of the structural unit, and the center frequency decreases as the size of the structural unit increases.

[0061] FSS loading the dielectric layer will not only improve the mechanical performance of the FSS structure, but also reduce the sensitivity of the entire FSS system to incident waves, and improve the stability of the performance when the incident waves are incident with different polarization modes and incident angles. The present invention further explores the influence of the two parameters of the dielectric layer thickness and the dielectric constant of the dielectric layer loaded on the curved FSS on its electromagnetic scattering characteristics.

[0062] Figure 4 Shown is the S-parameter transmission characteristic curve obtained by simulating and calculating the thickness d of the dielectric layer loaded on the side of the cylindrical FSS with a radius of curvature of 200 mm at equal intervals from 1 mm to 5 mm. It can be seen that as the thickness of the dielectric layer increases, the center resonance frequency of the cylindrical FSS shifts to low frequencies, and the speed of the center frequency shift gradually decreases, that is, when the frequency reaches about 3.1GHz, the center frequency shifts with the increase of the thickness. The speed slows down. This is because when the dielectric layer is thin, the interface between the free space and the dielectric layer is closer to the FSS, and the relative amplitude of the low-order modes and the stored energy around the FSS unit array change greatly, resulting in changes in the resonance frequency Big. When the dielectric layer reaches a certain thickness, the amplitude of these low-order modes and the energy storage around the FSS array unit remain basically stable, and the frequency of the FSS will tend to a fixed value.

[0063] During the frequency shift, the bandwidth and shape of the resonance band remain basically unchanged, that is, the ability to transmit and reflect electromagnetic waves remains unchanged. Therefore, for curved FSS, the thickness of the dielectric layer will only shift the center frequency at resonance without affecting the electromagnetic wave scattering ability.

[0064] Figure 5 Is the dielectric constant ε of the dielectric layer r Take the S-parameter transmission characteristic curves obtained after 2, 3, and 4 respectively. When the dielectric constant increases, the center frequency of the cylindrical FSS resonance shifts to low frequencies, while the shape of the S21 curve remains basically unchanged. This shows that within a certain range of dielectric constant, as the dielectric constant increases, the curved FSS The resonant frequency of will shift to low frequency, while the ability to scatter electromagnetic waves remains unchanged. In summary, the thickness and dielectric constant of the loaded dielectric layer will only shift the resonant frequency of the curved FSS, and will not greatly affect the electromagnetic wave scattering ability.