KR102129787B1 - Polarization-insensitive active frequency selective surface - Google Patents

Abstract

The present invention provides an active frequency selective surface (AFSS) including a dielectric substrate with a square structure in which a metal pattern is mounted on an upper/lower layer, while varactor diodes are mounted in a cross arrangement on the upper layer of the dielectric substrate, and two patches are symmetrically connected to each other through pin diodes on the lower layer of the dielectric substrate. Therefore, the AFSS provided by the present invention makes it possible switching between a transmission mode and an absorption mode and tuning frequency for operation modes while being insensitive to polarization. Particularly, the AFSS according to the present invention is implemented by using the pin diodes and the varactor diodes to offer short response times, wide tuning ranges, compact sizes and ease of use.

Description

Polarization-independent active frequency selection surface {POLARIZATION-INSENSITIVE ACTIVE FREQUENCY SELECTIVE SURFACE}

The present invention relates to a frequency selective surface, and more particularly, to a polarization-insensitive active frequency selective surface (Active Frequency Selective Surface, hereinafter referred to as'AFSS').

Due to the occurrence of countless electromagnetic waves due to the development of wireless communication and electronic devices, many problems such as communication errors, leakage of confidential information, and harmfulness of human body to harmful electromagnetic waves occur. A frequency selective surface has been proposed as a solution.

The frequency selective surface is widely used in various ways, such as stealth radome, multiple antenna, electromagnetic wave absorber, communication service, and wireless security system.

A frequency selective surface (FSS) is an electromagnetic filter in which a conductor is periodically patterned on a dielectric, and selectively transmits or reflects electromagnetic waves when any electromagnetic waves are incident in a designed driving frequency band.

However, the existing frequency selective surface research has a limitation in transmitting/reflecting only electromagnetic waves of a single frequency using a rigid metal dielectric substrate made of metal and dielectric.

Accordingly, pin diodes, varactor diodes, liquid crystals, ferro-electric substrates, radio frequency microelectromechanical systems (radio) Research on AFSS having transmission/reflection frequency variability using -frequency microelectronimechanial system) has been actively conducted.

In particular, methods using lumped reactive components (e.g., varactor diodes, PIN diodes, etc.) that undergo chemical reactions include short response times and wide tuning ranges. It has the advantage of providing tuning ranges, compact size, and ease of use. Accordingly, AFSS structures having multifunctional characteristics have been proposed based on these reactive components. For example, switchable absorbers/reflectors are narrow so that multiple PIN diodes provide an absorption or reflection response under different biasing states. It has been proposed for narrow band and broadband band applications. In addition, absorbers and filters that can be widely adjusted in frequency using varactors have been proposed.

On the other hand, recently, a multi-functional AFSS structure that provides three functions (transmission, reflection, and absorption) has been proposed. However, the structural design works for single-polarization and provides only switching characteristics without any tuning possibilities.

As such, conventional AFSSs cannot perform mode switching and frequency tuning at the same time. In addition, there has been no conventional AFSS with polarization-insensitive.

1.H.Li, Q.Cao, and Y.Wang, "A novel 2-B multifunctional active frequency selective surface for LTE-2.1 GHz," IEEE Trans.Antennas Propag., vol.65, no.6, pp. 3084-3092, Jun. 2017. 2.R.Phon, S.Ghosh, and S.Lim, "Novel multifunctional reconfigurable active frequency selective surface," accepted in IEEE Trans.Antennas Propag., 2018.

Accordingly, the present invention seeks to provide a polarization-insensitive active frequency selection surface in which the mode switching and frequency tuning characteristics simultaneously appear in the active frequency selection surface.

In order to achieve the above object, the active frequency selective surface provided by the present invention includes a dielectric substrate having a square structure in which a metal pattern is mounted on an upper/lower layer, but a plurality of varactors are formed on the upper layer of the dielectric substrate. It is characterized in that diodes (varactor diodes) are mounted in a cross arrangement, and two patches are symmetrically connected to the lower layer of the dielectric substrate through a plurality of pin diodes.

Preferably, the upper layer of the dielectric substrate is a first cross pattern of a metal material; And a second cross pattern of a metallic material surrounding the first cross pattern, wherein the first cross pattern can be connected to an extension line connected to the second cross pattern through the varactor diode. have.

Preferably, the first cross pattern may provide a resistance-inductance-capacitance effect generated by the varactor diode and a metal pattern.

Preferably, the second cross pattern may provide a resistance-inductive response from the metal pattern.

Preferably, the upper layer of the dielectric substrate may further include inductors connected in a bias direction of the second cross pattern from edges of the dielectric substrate.

Preferably, the upper layer of the dielectric substrate may symmetrically implement the first cross pattern, the second cross pattern, and the inductors.

Preferably, at least four pin diodes may be mounted on the lower layer of the dielectric substrate.

Preferably, the upper and lower layers of the dielectric substrate can be connected through metallic vias.

Preferably, the active frequency selection surface may operate in either a transmission mode or an absorption mode depending on the ON/OFF state of the pin diode.

Preferably, the transmission and absorption frequencies can be adjusted according to a change in the bias voltage of the varactor diodes.

Preferably, the dielectric substrate can be arranged in an n x n array to expand the operating frequency range.

The AFSS provided by the present invention has an advantage of being capable of switching between transmission mode and absorption mode and frequency tuning for the operation modes without being sensitive to polarization. In particular, the AFSS of the present invention is implemented by using a pin diode (pin diode) and a varactor diode (varactor diode), short response times (short response times), wide tuning ranges (wide tuning ranges), compact size ( compact size), and ease of use (ease of use).

1 is a view for explaining the unit cell structure of the active frequency selective surface according to an embodiment of the present invention.
2 is a view illustrating an AFSS lower layer layer of the present invention in which 8 pin diodes are used instead of 4 diodes.
3 is a diagram comparing the resonance frequency, insertion loss, and absorption rate of the case where four pin diodes are used for the lower layer of the AFSS of the present invention and when eight pin diodes are used when the reverse bias is 10 to 20 V.
4 is a diagram illustrating an equivalent circuit of the AFSS of the present invention.
FIG. 5 is a view showing the simulated scattering parameters simulated by AFSS of the present invention for each operation mode when the reverse voltage is 10 to 20 V.
FIG. 6 is a diagram showing the results of comparison of scattering parameters between the equivalent circuit model and full-wave electromagnetic wave simulation for the AFSS of the present invention for each operation mode when the reverse voltage is 20V.
7 is a view showing simulated scattering responses simulated by the AFSS of the present invention for various polarization angles for each operation mode in normal incidence.
FIG. 8 is a diagram illustrating simulated scattering responses by AFSS for each operation mode when oblique incidence.
9 is a diagram illustrating another embodiment of the AFSS of the present invention.
FIG. 10 is a diagram illustrating measured scattering parameters measured by AFSS according to the present invention for each operation mode when the reverse voltage is 10 to 20 V.
FIG. 11 is a diagram comparing the scattering parameters simulated by the AFSS of the present invention and the scattering parameters measured by the AFSS of the present invention by item when the reverse bias voltage is 10 to 20 V.
12 is a view showing a scattering parameter (S ₂₁ ) of the AFSS of the present invention for different tangential losses and different parasitic resistances when the reverse voltage is 10 V.
13 is a comparison table comparing the performance of conventional passive frequency selective surfaces and the active frequency selective surface of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings, and will be described in detail so that those skilled in the art to which the present invention pertains can easily implement the present invention. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the other hand, in order to clearly describe the present invention in the drawings, parts irrelevant to the description are omitted, and like reference numerals are assigned to similar parts throughout the specification. Also, even if a detailed description is omitted, a description of a part that can be easily understood by those skilled in the art is omitted.

Throughout the specification and claims, when a part includes a certain component, this means that other components may be further included instead of excluding other components unless specifically stated otherwise.

1 is a view for explaining a unit cell structure of an active frequency selective surface (AFSS) according to an embodiment of the present invention, Figure 1 (a) shows the top layer (top layer) of the AFSS, Figure 1 (b) shows the side surface of the AFSS, FIG. 1(c) shows the bottom layer of the AFSS, and FIG. 1(d) shows the perspective view of the AFSS.

The active frequency selective surface according to an embodiment of the present invention includes a dielectric substrate having a square structure in which a metal pattern is mounted on an upper/lower layer, with reference to FIGS. 1(a) to 1(d). The AFSS of the present invention will be described as follows.

First, referring to (a) of FIG. 1, a first cross pattern 17 made of metal and a second cross pattern made of metal surrounding the first cross pattern 17 on the upper layer of the dielectric substrate ( 16). At this time, the first cross pattern 17 includes a plurality of varactor diodes 11 to 14 mounted in a cross-array, and a plurality of varactor diodes 11 to 14 It is connected to the extension line connected to the second cross pattern 16 through. That is, the first cross pattern 17 is implemented inside the second cross pattern 16 and includes a plurality of varactor diodes 11 to 14. At this time, the first cross pattern 17 is a resistance generated by a plurality of varactor diodes (varactor diodes) (11 to 14) and a metal pattern (ie, a metal material that implements the first cross pattern 17). -Inductance-capacitance (resistance-inductance-capacitance) (R _t2 -L _t2 -C _v ) provides the effect, the second cross pattern 16 is a metal pattern (i.e., a metal that implements the second cross pattern 16) Material) to provide a resistance-inductive (R _t1 -L _t1 ) response.

In addition, the upper layer of the dielectric substrate may further include an inductor 15 connected in a bias direction of the second cross pattern 16 from corners of the dielectric substrate. At this time, it is desirable to optimize the value of the inductor 15 so that the reaction of the AFSS of the present invention is not affected.

In the example of the present invention, as illustrated in Table 1, varactors were modeled with a series circuit of R-L-C having a nonlinear variable value.

Reverse voltage (V) Rv(Ω) Lv(nH) Cv(pF) 10 2.5 0.2 0.42 12 2 0.2 0.36 14 One 0.2 0.32 16 0.9 0.2 0.31 18 0.6 0.2 0.29 20 0.4 0.2 0.28

On the other hand, the upper layer of the dielectric substrate is a first cross pattern 17, the second cross pattern 16 and inductors 15 are all implemented symmetrically. It is to realize the characteristics of the AFSS of the present invention independent of polarization.

In addition, the upper and lower layers of the dielectric substrate may be connected through metallic vias, whereby the vias are seen as illustrated in FIG. 1( b).

Referring to (c) of FIG. 1, two patches P1 and P2 are symmetrically connected to the lower layer of the dielectric substrate through a plurality of pin diodes 21 to 24, and an aperture type structure. Have At this time, the pin diodes (Pin diodes) (21 to 24) should include at least four, in the form of adding one to each side, it is possible to increase to 8, 12. An example of increasing the number of pin diodes to 12 is illustrated in FIG. 12, which further reduces the short-circuit resistance in the ON state by additionally connecting pin diodes in parallel, thereby reducing the short circuit resistance of the ON state. It has the effect of increasing the absorption rate of AFSS.

2 is a view illustrating an AFSS lower layer layer of the present invention in which 8 pin diodes are used instead of 4 diodes. Referring to FIG. 2, two patches constituting the AFSS lower layer of the present invention were connected using two pin diodes on each side. Therefore, the example of FIG. 2 shows an example in which 8 pin diodes are used as a whole.

3 is a diagram comparing the resonance frequency, insertion loss, and absorption rate of the case where 4 pin diodes are used for the lower layer of the AFSS of the present invention and 8 pin diodes are used when the reverse bias is 10 to 20 V. Referring to (b), it can be seen that the absorption rate of the AFSS of the present invention is improved to 73.92 to 96.64% for a 10 to 20 V reverse voltage, and in a similar manner, it is obvious that the insertion loss of the transmission mode is improved. . Referring to (a) of FIG. 3, it can be seen that as the number of diodes increases, the transmission frequency decreases slightly as the value of the off-state capacitance increases.

1(d) is a perspective view of the AFSS of the present invention, and shows an example in which the AFSS unit cells of the present invention are arranged in a 2×2 arrangement. As described above, as the AFSS unit cells of the present invention are expanded, the AFSS operating frequency range of the present invention is expanded, and it is preferable that the AFSS unit cells of the present invention are arranged in at least 10×10 arrangement.

Optimized physical dimensions for the AFSS of the present invention illustrated in FIG. 1 are as follows. In the example of FIG. 1, FR4 (ε _r =4.4 and tan δ = 0.02) has been used as an intermediate substrate, and the patterns at the top and bottom are imprinted in a periodic arrangement, and the dimension of each part shown in the figure is p = 10 mm, w = 0.5 mm, g = 1.2 mm, a = 3.5 mm, b = 0.3 mm, c = 0.2 mm, d = 1 mm, e = 1 mm, t = 1 mm. On the other hand, the pin diodes embedded in the lower layer are considered to have high capacitance (C _OFF = 0.17 pF) in the _OFF state and low resistance (R _ON = 3 Ω) in the _ON state.

The illustrated physical dimensions and capacitance and resistance values of the pin diodes are only illustrative of the optimized data, but the content of the present invention is not limited by the illustrated data.

AFSS of the present invention having such a configuration can adjust the transmission and absorption frequency according to the bias voltage (bias voltage) of the varactor diodes (varactor diode) (11 to 14) mounted on the upper layer of the dielectric substrate. In addition, the AFSS of the present invention is one of a transmission mode (transmission mode) or an absorption mode (absorption mode) according to the ON/OFF state of the pin diodes 21 to 24 mounted on the lower layer of the dielectric substrate. It can work. That is, when the pin diodes 21 to 24 are in an ON state, the AFSS operates in an absorption mode, and when the pin diodes 21 to 24 are in an OFF state, the AFSS Operates in transmission mode. This operation principle will be described in more detail with reference to the following drawings.

이다. 또한, 도 4의 예에서, 최적화된 파라미터는 다음과 같다. L_t1 = 3.05nH, L_t2 = 2.2nH, L_b1 = 2.09nH, L_b2 = 0.45nH, L_v = 0.2nH, R_t1 = 0.2Ω, R_t2 = 1.84Ω, R_b1 = 0.02Ω, R_b2 = 0.02Ω, R_ON = 3Ω, R_V,20V = 0.4Ω, C_OFF = 0.53pF, C_V,20V = 0.28pF.4 is a diagram illustrating an equivalent circuit of the AFSS of the present invention. FIG. 4(a) illustrates an equivalent circuit of a top layer including a varactor 10, and FIG. 4(b) shows an equivalent circuit of a bottom layer including a pin diode 20. To illustrate. In (a) and (b) of Figure 4, L _t1 , L _t2 represents the strip inductance of the upper layer due to the metal pattern, L _b1 , L _b2 represents the strip inductance of the lower layer due to the metal pattern, R _t1 , R _t2 represents the resistance of the upper layer due to the finite conductivity of the copper metal, and R _b1 , R _b2 represents the resistance of the lower layer due to the finite conductivity of the copper metal. On the other hand, Z ₀ and Z _TL represent the characteristic impedance of the free space and the dielectric spacer, respectively. At this time, Z _TL

to be. In addition, in the example of FIG. 4, the optimized parameters are as follows. L _t1 = 3.05nH, L _t2 = 2.2nH, L _b1 = 2.09nH, L _b2 = 0.45nH, L _v = 0.2nH, R _t1 = 0.2Ω, R _t2 = 1.84Ω, R _b1 = 0.02Ω, R _b2 = 0.02Ω, R _ON = 3Ω, R _V,20V = 0.4Ω, C _OFF = 0.53pF, C _V,20V = 0.28pF.

FIG. 5 is a view showing the simulated scattering parameters simulated by AFSS of the present invention when the reverse voltage is 10 to 20 V for each operation mode, and (a) of FIG. 5 is in transmission mode, (b) It shows simulated scattering parameters when in absorption mode.

When the AFSS of the present invention as illustrated in FIGS. 1 and 4 is operated in a transmission mode, the inductance and capacitance of the lower layer are connected in parallel with the reactive element of the upper layer. Thus, this slightly increases the overall capacitance. However, there is a feature that significantly reduces the effective inductance. This operating characteristic curve is illustrated in Fig. 5(a). Referring to FIG. 5(a), it can be seen that the original bandpass-bandstop pattern of the AFSS upper layer of the present invention is moved to a higher frequency in the AFSS structure. Therefore, through simulation, it can be seen that by changing the transformer reverse voltage of 10 to 20 V, the bandpass frequency can be adjusted from 3.62 to 4.16 GHz with an insertion loss of 0.99 to 3.40 dB.

Meanwhile, when the AFSS of the present invention as illustrated in FIGS. 1 and 4 is operated in an absorption mode, the lower layer provides only inductance (no capacitance) and functions as a grounded dielectric substrate. At this time, the upper layer response remains almost constant except for the blue shift and the large reduction in transmission in the frequency spectrum. This operating characteristic curve is illustrated in Fig. 5B. Referring to (b) of FIG. 5, it can be seen that the AFSS of the present invention can be determined to have a corresponding absorption rate of 4.98 to 91.17% by adjusting the band voltage to adjust the bandstop frequency between 4.28 and 5.10 GHz. .

FIG. 6 is a diagram showing results of comparison of scattering parameters between the equivalent circuit model and the full-wave electromagnetic wave simulation for the AFSS of the present invention for each operation mode when the reverse voltage is 20 V to verify the AFSS of the present invention. to be. 6(a) shows the comparison result in the transmission mode and FIG. 6(b) shows the comparison result in the absorption mode. Referring to FIG. 6, it can be seen that under the 20 V reverse voltage condition, scattering parameters of the circuit model and full-wave simulation results are very similar in both the transmission mode and the absorption mode.

FIG. 7 is a diagram showing the simulated scattering responses simulated by the AFSS of the present invention for various polarization angles at normal incidence, by operation mode, and FIG. 7(a) is a simulation in the transmission mode. Shows simulated scattering responses, and FIG. 7(b) shows simulated scattering responses in absorption mode. Referring to FIG. 7, it can be seen that the reaction remains the same for all polarization angles. This indicates that the polarization-insensitive characteristic of the AFSS of the present invention was well implemented.

FIG. 8 is a view showing simulated scattering responses by operation mode according to the present invention AFSS when oblique incidence, and FIG. 8( a) is simulated in transmission mode. scattering responses), and FIG. 8(b) shows simulated scattering responses in absorption mode. Referring to FIG. 8, it can be seen that the AFSS of the present invention shows angular stability up to an angle of occurrence of up to 60°.

FIG. 9 is a diagram illustrating another embodiment of the AFSS of the present invention, and illustrates a case in which unit cells for the AFSS of the present invention illustrated in FIG. 1 are arranged in a 2×2 arrangement. FIG. 9(a) shows the top layer for the other embodiment, FIG. 9(b) shows the bottom layer for the other embodiment, and FIG. 9(c) shows the Another embodiment shows a bias supply technique for a transmission mode, and FIG. 9D shows a bias supply technique for an absorption mode of another embodiment. At this time, reference numeral '100' denotes terminal 1, reference numeral '200' denotes terminal 2, and reference numeral '300' denotes terminal 3.

10 is a diagram showing the scattering parameters (measured scattering parameters) measured by the AFSS of the present invention when the reverse voltage is 10 to 20 V for each operation mode, and FIG. 10 (a) shows the measured scattering when operating in the transmission mode. Parameters (measured scattering parameters), Figure 10 (b) shows the measured scattering parameters (measured scattering parameters) when operating in the absorption mode. Referring to (a) of FIG. 10, it can be seen that the AFSS of the present invention can obtain an adjustable bandpass response of 3.70 to 4.27 GHz with 1.96 to 4.30 dB insertion loss in the transmission mode. In addition, referring to (b) of FIG. 10, it can be seen that the AFSS of the present invention can obtain an absorption rate of 78.77 to 90.78% by adjusting the frequency to 4.28 to 5.12 GHz in the absorption mode.

FIG. 11 is a diagram comparing the scattering parameters simulated by the present invention AFSS and the scattering parameters measured by the present invention AFSS by item when the reverse bias voltage is 10 to 20V. 11(a) resonance frequency comparison, FIG. 11(b) comparison of insertion loss and absorption rate, and FIG. 11(c) comparison of half-power bandwidth. Referring to FIG. 11, it can be seen that good results are obtained in all cases except for the dispersion characteristics of the parasitic elements, the finite size of the prototype, and some minor deviations that may be attributed to manufacturing tolerances.

12 is a view showing a scattering parameter (S ₂₁ ) of the AFSS of the present invention for different tangential losses and different parasitic resistances when the reverse voltage is 10 V. 12(a) shows an example of reducing the passband insertion loss from 3.40dB to 3.14dB by reducing the tangential losses of the dielectric substrate from 0.02 to 0. For this reason, insertion loss can be improved by using a low-loss dielectric material. On the other hand, Fig. 12 (b) shows an example of reducing the insertion loss of the passband from 3.40 dB to 0.92 dB by reducing the parasitic resistance of the varactor diode from 3 Ω to 0 Ω.

13 is a comparison table comparing the performance of AFSS of the present invention with conventional passive frequency selective surfaces. Referring to FIG. 13, the AFSS of the present invention is capable of both switching and frequency tuning in terms of operating functions, has dual polarization characteristics, and working mode It can be seen that mode) is the only thing that is possible for both transmission and absorption.

In the exemplary system described above, the methods are described based on a flow chart as a series of steps or blocks, but the present invention is not limited to the order of steps, and some steps may occur in a different order or simultaneously with other steps as described above. You can.

In addition, those skilled in the art will understand that the steps shown in the flowchart are not exclusive, other steps may be included, or one or more steps in the flowchart may be deleted without affecting the scope of the present invention.

Claims (11)

In the active frequency selection surface,
Including a dielectric substrate (dielectric substrate) of a square structure with a metal pattern mounted on the upper / lower layer,
On the upper layer of the dielectric substrate
A number of varactor diodes are mounted in a cross arrangement,
The lower layer of the dielectric substrate
The two patches are connected symmetrically through a number of pin diodes,
The upper layer of the dielectric substrate
A first cross pattern made of metal; And
Including a second cross pattern of a metal material surrounding the first cross pattern,
The first cross pattern
Active frequency selection surface, characterized in that connected to the extension line connected to the second cross pattern through the varactor diode (varactor diode). delete The method of claim 1, wherein the first cross pattern
An active frequency selective surface characterized in that it provides a resistance-inductance-capacitance effect generated by the varactor diode and a metal pattern. The method of claim 1, wherein the second cross pattern
An active frequency selective surface characterized by providing a resistance-inductive response from a metal pattern. According to claim 1, The upper layer of the dielectric substrate
And an inductor connected in a bias direction of the second cross pattern from corners of the dielectric substrate. The method of claim 5, wherein the upper layer of the dielectric substrate
The first cross-pattern, the second cross-pattern and the active frequency selective surface, characterized in that all implementing the inductors symmetrically. The method of claim 1, wherein the lower layer of the dielectric substrate
An active frequency selective surface, characterized in that at least four pin diodes are mounted. According to claim 1,
The top and bottom layers of the dielectric substrate are active frequency selective surfaces, characterized in that they are connected via metallic vias. The active frequency selective surface of claim 1,
According to the ON/OFF state of the pin diode, the active frequency selection surface is characterized in that it operates in either a transmission mode (transmission mode) or an absorption mode (absorption mode). The active frequency selective surface of claim 1,
An active frequency selection surface characterized in that the transmission and absorption frequencies are adjusted according to a change in the bias voltage of the varactor diodes. The method of claim 1, wherein the dielectric substrate
Active frequency selective surface characterized by widening the operating frequency range by expanding arrangement in nxn array.

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