In this paper, a miniaturized and polarization insensitive frequency selective surface filter with large band ratio (BR) is presented. This structure consists of one metal layer and two dielectric layers. The metal layer includes two parts, with the outer square loop providing a lower frequency stopband and the inner pattern providing a higher frequency stopband. The structure has excellent miniaturization characteristics, in particular, the unit size is only 0.054 λ 0 and the thickness is only 0.014 λ 0, where λ 0 is the wavelength corresponding to the first resonant frequency. Additionally, there is only one layer of metal layer, which greatly reduces the processing complexity and cost. The measurement results show that for TE and TM polarization, the center frequencies of the two stop bands are 2.03 and 18.98 GHz corresponding to a BR of 9.35. It can be used as a spatial dual frequency filter with large frequency band separation. In addition, the proposed structure also possesses advantages such as wideband response, polarization insensitivity, and high angle stability. The simulation results are in good agreement with the measured results.

Frequency selective surface (FSS) is a type of microwave device with periodic array structures, which plays the role of spatial filters for electromagnetic waves with different incidence angles and different polarization modes.1 It is widely used in wireless communication, radar and antenna fields, such as various antenna reflectors, radomes, absorbers, shields, polarizers, detector and reduction of radar cross section (RCS), etc.2–11 

With the rapid development of wireless communications, radar, and satellite communications, the design and fabrication of dual-band or multi-band FSSs have attracted increasing attention.12 A multi-band FSS facilitates the adjustment of frequency bands, reduces system footprint, and additionally enables stealth capabilities.13There are several main techniques for designing dual-band or multi-band FSSs: (1) fractal elements,14 (2) multiple resonant elements,15 (3) multi-layer structures,16 (4) single-frequency FSSs with resonant primitives,17 and so on. Most of the existing designs focus on applications with closely spaced operating frequency bands.18 These designs rely on coupled resonant structures, where the resonant characteristics of the unit cells are modified to achieve the tightest possible frequency separation between adjacent bands. In practical scenarios, achieving outstanding multi-band responses with a large band ratio (BR), where BR represents the ratio of the resonant frequencies of two band-stop windows, becomes challenging due to harmonic resonances and grating flaps. It has been documented by Li et al. that angular stability degrades rapidly in the majority of multi-frequency band FSSs when the BR is relatively large.19 Researchers need to ensure effective separation of the two resonant frequencies within a limited size by cleverly designing the unit cell shape, coupling mechanisms, and material properties, while preventing interference or overlap between the structures.

In recent years, a number of researchers have attempted to design FSS structures with large band ratio.20–24 For example, in 2014, Li et al.20 proposed a three-dimensional bandpass FSS, consisting of a set of three-layer printed circuit boards and some inserted metal rods and plates, to achieve high frequency dual-band performance, with a BR of 4.2. In 2019, Li et al.21 proposed a three-layer spurious-free structure design to obtain a relatively large BR. However, both of the above FSS are unipolar. Based on the staggered grid structure, Jiang et al.22 combined two square grid FSSs together to enhance the band stop response of FSSs, resulting in a wider bandwidth between the two passbands, thereby increasing BR to 6.2. However, the above structures are three-dimensional, complicated to fabricate, and the BR is not high enough.

Therefore, unlike existing works that employ complex multi-layer or three-dimensional structures, this paper proposes a miniaturized and polarization insensitive FSS filter with large BR, which is a simple single-layer metallic FSS design, making it easier to fabricate. The schema and working principles are illustrated in Fig. 1. Guided by the theory of equivalent circuit model (ECM), the internal complex combination model is designed from the dual square loop model, which increases the BR and improves the angular stability of the structure. Utilizing a configuration that incorporates a metal layer and a double-layer dielectric substrate, the resonant frequency of the low-frequency operating band was reduced, thereby further augmenting the BR. This approach also ensured the durability and stability of the FSS. The reliability of the theoretical analysis and simulation was validated through empirical measurements. This type of FSS filter with a large BR offers advanced spectral filtering capabilities, promising significant advancements in communication systems, radar stealth, satellite communication, and environmental sensing, addressing challenges in electromagnetic compatibility and component miniaturization.

FIG. 1.

The schematic diagram of the proposed FSS.

FIG. 1.

The schematic diagram of the proposed FSS.

Close modal

The arrangement of the remaining chapters is as follows: Section II presents the structural description and operating mechanism of the designed FSS. Section III verifies the dual stop band transmission performance through full-wave simulation as well as microwave darkroom testing, and the measured results are in good agreement with the simulated results. Section IV gives the conclusion.

The proposed FSS structure is a single layer structure with a thin dielectric layer above and below the main metal layer in the center as shown in Fig. 2. It mainly consists of two dielectric layers with a patch-type metal layer in the middle. This FSS is assembled by a parallel tightly arranged along the x and y directions, which provides polarization insensitivity. Based on the basic single-layer FSS, a tightly fitting dielectric substrate is added to further reduce the operating range of the low-frequency stop band, thereby increasing the BR, and also protecting the intermediate metal layer to improve its durability.

FIG. 2.

Three-dimensional structure diagram of the proposed dual-band FSS.

FIG. 2.

Three-dimensional structure diagram of the proposed dual-band FSS.

Close modal

The structure of each unit is shown in Fig. 3, which mainly consists of an outer metal loop and an inner center-symmetric structure. The centrosymmetry of the inner layer is a combination of a group of concentric rings and an improved swastika, and Fig. 4 illustrates the evolution of the internal structure design. The evolution process begins with the classical swastika-shaped structure composed of four bent branches, on each of which a smaller rectangular fractal is added. Next, a T-shaped structure is split from the ends of the four branches. Finally, a dual-ring patch is connected in series. This design approach enhances the effective path of the internal complex pattern, thereby achieving a miniaturized unit. This FSS uses FR-4 with a relative permittivity ε r = 4.3 and loss tangent tan δ = 0.025 as the substrate, and the metal layer is made of copper.

FIG. 3.

Plan structure diagram of the FSS metal layer.

FIG. 3.

Plan structure diagram of the FSS metal layer.

Close modal
FIG. 4.

Evolution of the internal structure design.

FIG. 4.

Evolution of the internal structure design.

Close modal
The dual loop model has been widely studied in the past. Forming a dual-stopband FSS is relatively simple and can be achieved by printing two square loops directly on the substrate. For two square loops, they can be explained by the ECM shown in Fig. 5(a), which is modeled as a parallel connection between a series connected L 1 C 1 resonator and another series connected L 2 C 2 resonator.
(1)
FIG. 5.

(a) Equivalent circuit model of general two square Loop FSS. (b) Equivalent circuit model of the proposed FSS. L 1 = 3.55 nH, C 1 = 0.02 pF, R 1 = 36.76 Ω, L 2 = 16.20 nH, C 2 = 0.36 pF.

FIG. 5.

(a) Equivalent circuit model of general two square Loop FSS. (b) Equivalent circuit model of the proposed FSS. L 1 = 3.55 nH, C 1 = 0.02 pF, R 1 = 36.76 Ω, L 2 = 16.20 nH, C 2 = 0.36 pF.

Close modal
Therefore, the simplified ECM of the proposed FSS model in this paper is shown in Fig. 5(b). The transmission line has a characteristic impedance Z = Z 0 / ε r and a total length h, where ε r is the dielectric permittivity of the substrate and Z 0 = 377 Ω is the impedance of free space. L 1 and L 2 represent the internal structure and the outer metal loop, respectively. C 1 represents the coupling capacitance formed by the internal gap of the internal structure. C 2 represents the coupling capacitance between the metal loop and the internal structure. Resistances ( R 1) in ECM represent the losses in the dielectric substrate. L 2, C 2 represent standard square loop, which can be calculated by formula (2) and (3) to derive the initial values.
(2)
where
(3)
where G is the correction term and ε e f f is the equivalent permittivity affected by substrate thickness and relative permittivity.
According to the calculation formula (4) and (5) and the quasi-static analysis of the microstrip lines,25 the rough values of L 1 can be deduced. The complex structure in the middle is simplified into a swastika structure and a double ring structure. A swastika structure is split into a combination of four curves, represented by L s 1, L s 2, L s 3, L s 4, respectively.26 Since the length and width of the four curves are the same, their corresponding inductance values are also the same,
(4)
For the double ring structure, the inductance values ( L c 1, L c 2) of the outer ring and the inner ring need to be calculated separately,
(5)
where CT is a correction term defined based on the diameter of the ring.27 

The inductance value of the swastika structure is the series sum of the four identical curved segments. The coupled inductance of the double ring is the parallel value of the two rings. Therefore, the rough value of L 1 is the inductance value of the swastika structure and the double ring structure connected in series. Then, the advanced design system (ADS) is used for curve fitting and optimization to obtain all parameters. The frequencies of two different stopbands can be calculated using formula (1).

Simulate the equivalent circuit using ADS, the capacitance and inductance values obtained through curve fitting optimization are shown in Fig. 5. The S-parameters obtained from CST simulation and the ECM are shown in Fig. 6(a). From the results, it can be seen that the two stopbands are located at 2.03 and 18.98 GHz, respectively, and the equivalent circuit model results are generally consistent with the full wave simulation results.

FIG. 6.

(a) Comparison of the S-parameters under normal incidence. Full wave electromagnetic simulation results and ECM prediction results are provided. (b) Comparison of S-parameters in TE and TM polarization modes.

FIG. 6.

(a) Comparison of the S-parameters under normal incidence. Full wave electromagnetic simulation results and ECM prediction results are provided. (b) Comparison of S-parameters in TE and TM polarization modes.

Close modal

Based on the analysis of the basic dual loop model, this paper proposes a dual-stopband FSS filter. The outer layer of a very slender square loop metal can provide a very small resonant frequency band. The inner layer is made of a modified swastika-shaped graphic, which ensures the axial and central symmetry of the structure, thus improving the angular stability as well as the polarization insensitivity. Designing such complex internal structures can improve the stability of FSSs at large BR and increase the level of miniaturization. The upper dielectric substrate can further reduce the low resonant frequency, thereby improving BR, and also protect the middle metal layer to improve the durability of FSSs.

Figure 7 displays the variation of the calculated transmittivity with increasing incidence angle at TE and TM polarizations. The results indicate that the transmittivity remains stable when the incident angle increases from 0 ° to 45 °. The transmittivity can be calculated as T = | S 21 | 2.

FIG. 7.

The transmittivity of the proposed FSS varying with incident angle. (a) TE polarization; (b) TM polarization.

FIG. 7.

The transmittivity of the proposed FSS varying with incident angle. (a) TE polarization; (b) TM polarization.

Close modal

In order to verify the performance of the proposed FSS, the insertion loss at different polarization angles was simulated. Figure 6(b) shows the simulated frequency response characteristics of dual-stopband FSS under TE and TM polarization at normal incidence. The results indicate that compared to the ordinary dual-loop FSS, this structure has a wider passband bandwidth, achieving a passband above 16.9GHz, and achieving a stopband window with insertion loss less than 10dB in the range of 1.25–3.11 GHz and 18.70–19.20 GHz. The simulation results show that the center frequencies of the first and second stopbands are 2.03 and 18.98 GHz, respectively. The passband range of 10dB or more between two stopbands is 3.11–18.70 GHz, with a relative bandwidth of 143.0%. Moreover, the FSS maintains polarization insensitivity.

Furthermore, the main parameters of complex structure have also been varied to study the change in the resonance behavior. It can be observed from Fig. 8 that effective inductance increases with l 1 increases from 1.3 to 1.6 mm, the high-frequency decreases from 18.98 to 17.17 GHz. This leads to a reduction of frequency band ratio from 9.35 to 8.46. Similarly, as d 1 decreases from 0.5 to 0.1 mm, the performance changes are the same as l 1. Simultaneously, the first stopband can also be tuned by adjusting the dimensions of the outer square loop. By multiplying Eqs. (2) and (3), the calculation formula for L 2 C 2 can be obtained, further revealing that L 2 C 2 / d 2 < 0. Consequently, as d 2 increases (as the outer square loop becomes thicker), the value of L 2 C 2 decreases. According to Eq. (1), this results in a higher resonant frequency for the first stopband. Similarly, L 2 C 2 / d 3 < 0, indicating that L 2 C 2 is monotonically decreasing with respect to d 3. This implies that as the spacing between the outer square loops increases, the resonant frequency also rises. Through the study of parameters, a more comprehensive analysis of the electromagnetic behavior of the FSS can be achieved. The optimized parameters chosen for proposed miniaturized FSS are presented in Table I.

FIG. 8.

The simulated transmission spectrums of the proposed FSS. (a) For different values of l 1, and (b) for different values of d 1.

FIG. 8.

The simulated transmission spectrums of the proposed FSS. (a) For different values of l 1, and (b) for different values of d 1.

Close modal
TABLE I.

Physical parameters of the FSS in Fig. 3.

Parameter D h l1 l2 l3 R1 R2 
Value (mm) 1.3 0.7 0.3 0.9 0.7 
Parameter R3 R4 w1 w2 d1 d2 d3 
Value (mm) 0.6 0.4 0.1 0.2 0.4 0.1 0.05 
Parameter D h l1 l2 l3 R1 R2 
Value (mm) 1.3 0.7 0.3 0.9 0.7 
Parameter R3 R4 w1 w2 d1 d2 d3 
Value (mm) 0.6 0.4 0.1 0.2 0.4 0.1 0.05 

To further validate the simulation results, FSS has been fabricated and measured. The prototype consists of 40 × 40 unit cells, with a total size of 340 × 340 mm. The diagram of the measuring device is shown in Fig. 9. The transmitting and receiving antennas are both linearly polarized horn antennas used for transmitting and receiving electromagnetic wave signals. The transmitting antenna is located on the mechanical rocker arm above, and the receiving antenna is located on the mechanical rocker arm in the orange small darkroom below. The rotation angle is controlled by a computer, and the transmitting and receiving antennas are always in the same straight line as the prepared FSS during measuring. The transmitted and received signal levels were analyzed by Vector Network Analyzer (VNA) to calculate the transmittance of the FSS. In the measurement process, in order to verify the angular stability of the FSS, the computer control the tilt angle of the robotic arm simultaneously, so as to change the tilt angle theta of the transmitting and receiving antennas. To verify the polarization insensitivity of FSS, measurements were made by rotating two antennas at 90 °, using time-domain gating technology to eliminate multipath interference during testing.

FIG. 9.

Photos of measuring devices (transmitting–receiving antennas) and fabricated FSSs.

FIG. 9.

Photos of measuring devices (transmitting–receiving antennas) and fabricated FSSs.

Close modal

Figures 10 and 11 show the simulated and measured insertion loss of the dual-stopband FSS under TE and TM polarization oblique incidence. For TE polarization, as theta increases, the first stopband always maintains good stability and the range remains basically unchanged. The bandwidth of the second stopband is widened, but the frequency position is shifted slightly forward. From the measurement results, it can be seen that when the incident angle theta=30 °, the frequency range of the second stopband is 17.96–18.68 GHz, and the center frequency is 18.32 GHz. When theta = 45 °, the frequency range of the second stopband is 17.10–17.90 GHz, and the center frequency is reduced to 17.50 GHz. However, at this time, its BR is 8.6, which still maintains a large band ratio. When theta increases, there is some deviation in the S-parameters, which can be attributed to factors such as phase variations, increased penetration depth, and multi-mode effects. For TM polarization, as theta increases, the first and second stop bands always maintain good stability. From Figs. 10(b) and 11(b), it can be seen that the measurement results and simulation results are consistent within the error range. The reason for the error is due to the immature sample processing technology and defects in the testing environment. Overall, this FSS structure maintains good angular stability.

FIG. 10.

Comparison of transmission coefficients under different incident angles. (a) TE mode, simulation. (b) TE mode, measuring.

FIG. 10.

Comparison of transmission coefficients under different incident angles. (a) TE mode, simulation. (b) TE mode, measuring.

Close modal
FIG. 11.

Comparison of transmission coefficients under different incident angles. (a) TM mode, simulation. (b)TM mode, measuring.

FIG. 11.

Comparison of transmission coefficients under different incident angles. (a) TM mode, simulation. (b)TM mode, measuring.

Close modal

The performance comparison is shown in Table II. Compared with the work in the references, the FSS proposed in this paper has advantages such as miniaturization, large BR, dual polarization, and ultra wide passband. Moreover, most of the FSS in the literature are 3D structures, which are relatively complex to manufacture and have limitations in practical application. However, the FSS proposed in this article is a single-layer structure based on PCB technology, with low cost and easy production. The upper dielectric substrate can further protect the core structure of FSS, improving its durability.

TABLE II.

Performance comparison with existing designs.

ReferenceUnit element sizeThicknessPolarizationAngular stabilityNumbers of layersRelative bandwidthBR
19  0.072λ0 0.034λ0 Single 45° 3D 116.7% 5.0 
20  0.083λ0 0.045λ0 Single 40° 3D 109.7% 4.2 
22  0.081λ0 0.139λ0 Dual 40° 3D 116.6% 6.2 
23  0.090λ0 0.033λ0 Dual 30° 60.0% 5.4 
24  0.147λ0 0.019λ0 Single NA 66.7% 3.5 
This work 0.054λ0 0.014λ0 Dual 45° 143.0% 9.4 
ReferenceUnit element sizeThicknessPolarizationAngular stabilityNumbers of layersRelative bandwidthBR
19  0.072λ0 0.034λ0 Single 45° 3D 116.7% 5.0 
20  0.083λ0 0.045λ0 Single 40° 3D 109.7% 4.2 
22  0.081λ0 0.139λ0 Dual 40° 3D 116.6% 6.2 
23  0.090λ0 0.033λ0 Dual 30° 60.0% 5.4 
24  0.147λ0 0.019λ0 Single NA 66.7% 3.5 
This work 0.054λ0 0.014λ0 Dual 45° 143.0% 9.4 

This paper presents a miniaturized and polarization insensitive FSS filter with large BR. The proposed FSS offers significant advantages, including a large BR, polarization insensitivity, ultra-wideband characteristics, simple fabrication, and high durability. The measurement results of the fabricated FSS are generally consistent with the simulation results within the margin of error, demonstrating stable performance at large frequency band separations. This type of FSS with large BR holds substantial application potential in wideband communication and stealth technology.

The authors would like to thank the reviewers for their valuable comments and suggestions. This work was supported by the Postdoctoral Fellowship Program of CPSF (No. GZC20232050), Fundamental Research Funds for the Central Universities (No. 20106244406), and Aeronautical Science Foundation of China (No. 20240025081001).

The authors have no conflicts to disclose.

Yi Li: Conceptualization (equal); Data curation (equal); Funding acquisition (equal); Investigation (equal); Methodology (equal); Software (equal); Supervision (equal); Validation (equal); Visualization (equal); Writing – original draft (equal); Writing – review & editing (equal). Ruize Xu: Conceptualization (equal); Data curation (equal); Funding acquisition (equal); Investigation (equal); Methodology (equal); Software (equal); Supervision (equal); Validation (equal); Visualization (equal); Writing – original draft (equal); Writing – review & editing (equal). Peng Ren: Conceptualization (equal); Formal analysis (equal); Methodology (equal); Project administration (equal); Resources (equal); Supervision (equal); Writing – review & editing (equal). Baoyi Xu: Conceptualization (equal); Funding acquisition (equal); Resources (equal); Writing – review & editing (equal). Minrui Wang: Conceptualization (equal); Data curation (equal); Funding acquisition (equal); Investigation (equal); Project administration (equal); Resources (equal); Validation (equal); Writing – review & editing (equal). Chen Chen: Data curation (equal); Investigation (equal); Software (equal); Validation (equal). Keqing Chen: Data curation (equal); Investigation (equal); Software (equal); Validation (equal); Visualization (equal). Zheng Xiang: Conceptualization (equal); Funding acquisition (equal); Investigation (equal); Project administration (equal); Resources (equal); Validation (equal); Visualization (equal); Writing – review & editing (equal).

The data that support the findings of this study are available from the corresponding author upon reasonable request.

1.
B. A.
Munk
,
Frequency Selective Surfaces: Theory and Design
(
John Wiley & Sons
,
2005
).
2.
E. M.
Materon
,
H. R. D.
Filgueiras
,
E. C.
Vilas Boas
,
F. R.
Gómez
,
F. R. P.
Cavalcanti
,
Y. C. B.
Silva
,
A.
Cerqueira S
,
F.
de Figueiredo
,
L. L.
Mendes
,
O. N.
Oliveira
et al., “
Flexible metasurfaces as sub-6 GHz frequency selective surfaces for 5G applications
,”
J. Appl. Phys.
134
,
145304
(
2023
).
3.
A.
Bhardwaj
,
A.
Anand
,
D.
Tiwari
,
K.
Mehendiratta
,
V.
Jha
,
U. N.
Mishra
, and
M. G.
Siddiqui
, “
Frequency selective surface (FSS) based ultra-wideband (UWB) antenna for frequency filtering applications
,”
AIP Conf. Proc.
3131
,
030011
(2024).
4.
Y.
Jia
,
H.
Zhai
,
C.
Guo
, and
L.
Song
, “
A dual-band composite frequency selective rasorber with broadband absorption performance
,”
IEEE Antennas Wirel. Propag. Lett.
22
,
1992
1996
(
2023
).
5.
M.
Khodzitsky
,
A.
Tukmakova
,
D.
Zykov
,
M.
Novoselov
,
I.
Tkhorzhevskiy
,
A.
Sedinin
,
A.
Novotelnova
,
A.
Zaitsev
,
P.
Demchenko
,
E.
Makarova
et al., “
THz room-temperature detector based on thermoelectric frequency-selective surface fabricated from Bi 88Sb 12 thin film
,”
Appl. Phys. Lett.
119
,
164101
(
2021
).
6.
K.
Naik
and
K.
Naik
, “
An analysis of dual slot antenna using frequency selective surface for ultra wideband applications
,”
AIP Conf. Proc.
2494
,
050005
(2022).
7.
F.
Zhao
,
J.
Wang
,
D.
Feng
,
Q.
Wu
, and
X.
Liu
, “
Time-modulated active frequency selective surface absorber/reflector for spectrum conversion
,”
J. Appl. Phys.
131
,
035101
(
2022
).
8.
P.
Xu
,
L.
Li
,
R.
Li
, and
H.
Liu
, “
Dual-circularly polarized spin-decoupled reflectarray with FSS-back for independent operating at Ku-/Ka-bands
,”
IEEE Trans. Antennas Propag.
69
,
7041
7046
(
2021
).
9.
S. N.
Azemi
,
N. A.
Ibrahim
,
A.
Amir
,
R. C.
Beson
, and
M. E.
Abdul Aziz
, “
Design of passive RFID tag using frequency selective surface with polarization insensitive
,”
AIP Conf. Proc.
2579
,
020008
(2023).
10.
Z.
Huang
,
Y.
Liu
,
Q.
Cao
,
Y.
Zhao
,
Z.
Cao
,
S.
Guo
,
L.
Miao
, and
J.
Jiang
, “
Partition layout loading of frequency selective surface absorbers on the curved surfaces for the significant RCS reduction
,”
IEEE Trans. Microwave Theory Tech.
70
,
2948
2954
(
2022
).
11.
C.
Du
,
H.
Chen
,
S.
Wang
,
Y.
Pang
,
T.
Zhou
,
S.
Xia
, and
D.
Zhou
, “
Dual-polarized angle-selective surface based on double-layer frequency selective surface
,”
Appl. Phys. Lett.
124
,
111701
(
2024
).
12.
P.
Chomtong
,
P.
Krachodnok
,
K.
Bandudej
, and
P.
Akkaraekthalin
, “
A multiband FSS director using aperture interdigital structure for wireless communication systems
,”
IEEE Access
10
,
11206
11219
(
2022
).
13.
W.
Gong
,
W.
Zhang
,
X.
Chen
,
G.
Han
,
L.
Han
,
J.
Su
, and
R.
Yang
, “
A low-profile energy selective surface with ultra-wide absorption band
,”
IEEE Trans. Microwave Theory Tech.
71
,
1348
1355
(
2023
).
14.
L.
Murugasamy
and
R.
Sivasamy
, “
A novel fractal inspired iterated four-legged loaded loop elements based 2.5-D miniaturized frequency selective surface
,”
IEEE Trans. Electromagn. Compat.
63
,
2164
2167
(
2021
).
15.
D.
Wang
,
W.
Che
,
Y.
Chang
,
K.-S.
Chin
, and
Y.-L.
Chow
, “
Combined-element frequency selective surfaces with multiple transmission poles and zeros
,”
IET Microwaves, Antennas & Propagation
8
,
186
193
(
2014
).
16.
M. A.
Al-Joumayly
and
N.
Behdad
, “
Low-profile, highly-selective, dual-band frequency selective surfaces with closely spaced bands of operation
,”
IEEE Trans. Antennas Propag.
58
,
4042
4050
(
2010
).
17.
Z.-F.
Wang
,
M.-F.
Pan
,
Z.-Y.
Zong
,
W.
Wu
, and
D.-G.
Fang
, “
A novel dual-band frequency selective surface using the element combined with left-handed unit and capacitive grid
,”
IEEE Antenna Wirel. Propag. Lett.
11
,
1198
1201
(
2012
).
18.
M.
Idrees
,
Y.
He
,
S.
Ullah
, and
S.-W.
Wong
, “
A dual-band polarization-insensitive frequency selective surface for electromagnetic shielding applications
,”
Sensors
24
,
3333
(
2024
).
19.
B.
Li
and
Z.
Shen
, “Dual-band frequency selective structure with large frequency band ratio,” in 2013 IEEE MTT-S International Microwave Workshop Series on RF and Wireless Technologies for Biomedical and Healthcare Applications (IMWS-BIO) (IEEE, 2013), pp. 1–3.
20.
B.
Li
and
Z.
Shen
, “
Dual-band bandpass frequency-selective structures with arbitrary band ratios
,”
IEEE Trans. Antennas Propag.
62
,
5504
5512
(
2014
).
21.
D.
Li
,
Z.
Shen
, and
E.-P.
Li
, “
Spurious-free dual-band bandpass frequency-selective surfaces with large band ratio
,”
IEEE Trans. Antennas Propag.
67
,
1065
1072
(
2019
).
22.
P.
Jiang
,
W.
Jiang
,
W.
Hu
, and
S.
Gong
, “
An interlaced grid dual-band dual-polarized bandpass FSS with a large band ratio
,”
IEEE Antenna Wirel. Propag. Lett.
21
,
1027
1031
(
2022
).
23.
Z.
Zhao
,
G.
Wan
, and
X.
Huang
, “Design of dual-band frequency selective surface with large band ratio for 5G communication,” in 2020 IEEE 3rd International Conference on Electronics Technology (ICET) (IEEE, 2020), pp. 756–759.
24.
K.
Kaur
and
A.
Kaur
, “
Frequency selective surfaces (FSS) for S and X band shielding in electromagnetic applications
,”
AIP Conf. Proc.
2576
,
030015
(2022).
25.
J.-S. G.
Hong
and
M. J.
Lancaster
,
Microstrip Filters for RF/Microwave Applications
(
John Wiley & Sons
,
2004
).
26.
L.
Murugasamy
and
R.
Sivasamy
, “
A single layer interdigitated loop elements-based miniaturized frequency selective surface for WLAN shielding
,”
IEEE Trans. Consumer Electronics
70
,
617
626
(
2024
).
27.
A.
Kapoor
,
P.
Kumar
, and
R.
Mishra
, “
Modelling of wideband concentric ring frequency selective surface for 5G devices
,”
Comput. Mater. Continua
75
,
341
361
(
2023
).