Dual-band Frequency Selective Surface Research Articles

Higher Order Bandpass Single and Dual Band Frequency Selective Surfaces With Aperture Coupled Patch Resonators

Higher Order Bandpass Single and Dual Band Frequency Selective Surfaces With Aperture Coupled Patch Resonators

Novel Dual Band Frequency Selective Surface and its Applications on the Gain Improvements of Compact UWB Monopole Antenna

In this work, a highly directional ultra-wideband (UWB) microstrip patch antenna as a single-element is suggested. The proposed antenna’s gain is enhanced with a novel dual-band frequency selective surface (FSS) placed beneath it. The FSS design has a hexagonal structure with meander line inductances and a capacitance-like structure connecting all of the corners to the middle. There is no metallic layer on the other side of the substrate, which shows transmission zeros at 4.95 GHz and 12.7 GHz, and a modified U-shaped monopole antenna is developed. First, the performance characteristics of the antenna and FSS are analyzed from the simulation results, and they are validated experimentally after fabrication, followed by measurement. The compact configuration comprises an antenna loaded with the proposed FSS results S11 less than -10 dB from 3.15 GHz to 22.65 GHz, covering the UWB band together with the X, Ku-band with a bandwidth of 19.5 GHz (151.16% FBW). The antenna’s overall physical dimensions would be 38.8 mm×38.8 mm×25.2 mm (0.407λo×0.407λo×0.265λo), with λo denoting the lowest frequency’s free-space wavelength. The FSS loading results in a 9.9 dBi maximum gain at 10 GHz. The antenna’s small size increases bandwidth, and its high peak gain makes it ideal for use in real-time applications.

An optically transparent dual-band frequency selective surface for polarization independent RF shielding

This article reports on a compact dual band, Frequency Selective Surface (FSS) based spatial filter for Wi-Fi and WLAN shielding applications on a transparent glass surface with optical transparency of 70%. The unit cell comprises an outer square loop resonator with a disconnected and concentric annular ring resonator. To introduce frequency tuning and compactness T shape stubs are strategically loaded on these resonators and it is ensured that the mutual coupling remains minimal. The outer square resonator suppresses the 2.4 GHz band, and the inner circular ring resonator stops the 5.4 GHz band. The unit element is four-fold symmetric thus it offers complete polarization independence. A detailed parametric and electromagnetic field analysis has been conducted to elucidate the significance of different sections of the unit element. An equivalent lumped circuit model is also derived for the proposed unit element to better explain the underlying working mechanism. A finite prototype of 15 × 11 elements is fabricated on a soda lime float glass by using ordinary adhesive copper foils with a standard chemical etching process. Polarization independence and angular stability up to 45° are measured and compared with the simulated responses. The FSS shield offers frequency suppression up to 45 dB and 43 dB for 2.4 GHz and 5.4 GHz bands respectively. With high optical transparency, the design allows maximum light through it and causes no extra burden on energy consumption for indoor applications. The compact dual band design and the possibility of direct application on host surfaces like glass windows and doors make this design an excellent candidate for data security and privacy applications in secure installations with an esthetically pleasing outlook.

A single layer and very close band spacing frequency selective surface with enhanced isolation

An ultrathin and very closely located dual-band frequency selective surface (FSS) with enhanced isolation is proposed in this letter. The unit cell consists of two typical concentric hexagon rings, with several stubs loaded on each side of the inner ring. Through the stub-loaded configuration, the mutual coupling of adjacent resonators is highly decoupled and a very close band spacing FSS with better isolation can be achieved, and the ratio of the two operating bands can be as low as 1.06. Additionally, due to the independent resonant frequencies, the band ratio can be set over a wide range, from 1.06–2.43. Furthermore, the corresponding equivalent circuit model (ECM) is developed and analyzed for better comprehension of the underlying mechanisms of the proposed FSS. The validity of the design is then checked with a prototype, and the measured results show good agreement with the simulated ones.

A Dual-Band Composite Frequency Selective Rasorber With Broadband Absorption Performance

In this paper, a dual-band frequency selective rasorber(FSR) is proposed based on a composite absorption structure. The FSR is a three-tier structure composed of lossy layer I, lossy layer II and a dual-band frequency selective surface (FSS). The lossy layer I is composed of a lossy cross-shaped structure in which, dual-passband resonators are added and constructed by parallel interdigital capacitors and meandering strip inductors(PLC). The lossy layer II is composed of a hybrid circular strip resonator loaded with lossy elements. FSS is implemented in two Jerusalem slots. By combining the lossy layers I and II as a composite lossy structure, the absorption bands of lossy layers I and II are successfully connected in the frequency response, and the bandwidth of S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> under -10dB is extended from 3.1 to 20.6GHz. The proposed FSR integrate dual-band, dual-polarized, and broadband absorption performance simultaneously. Finally, a prototype of the composite FSR is fabricated to validate the simulated results.

Dual-Band Frequency Selective Surface with Different Polarization Selectivity for Wireless Communication Application.

This article proposes a dual-band, frequency- and polarization-selective surface. Multiple resonant modes are introduced using the U-shaped resonator with a ground via to achieve dual-band responses and polarization selectivity. Two symmetrically grounded U-shaped resonators are coupled through electrically coupled apertures in a common ground, resulting in a passband with two transmission zeros per polarization. A general design flowchart and additional examples at the S, X, and K-bands are presented as well. A prototype at X-band is analyzed, fabricated, and measured, showing the passband center frequencies of 9.68 GHz and 10.73 GHz, factional bandwidths of 3.45% and 3.48%, and insertion losses of 0.9 dB and 1.1 dB, respectively. Due to the high selectivity, small frequency ratio, low profile, and stable performance under oblique incidence, the proposed designs have application potential in wireless communication systems.

3-D Printed Dual-Band Frequency Selective Surfaces for Radome Applications

In this study, dual-band frequency selective surface (FSS) structures are designed by using 3-D printing technology for antenna radome applications. Four different configurations are studied to find the best alternative for FSS substrate not only for electromagnetic (EM) responses but also for its mechanical properties suitable for radomes. To ease the manufacturing process, a conductive paint is also studied instead of copper microstrip lines. In addition, graphite is also used for the comparison. Different 3-D printed configurations, various thickness values and three different materials for conductive part are examined and compared to find the most efficient radome structure.

Single-layer frequency selective dual-band reflectarray operating at 28 GHz and 39 GHz

We report a single-layer frequency selective dual band reflectarray operated at 28 and 39GHz simultaneously. The reflectarray consists of cross dipole and spiral elements aligned on the surface of a substrate and dual band frequency selective surfaces aligned on the rear side. We aligned the cross dipole and spiral elements that can control the reflection direction at 28 and 39GHz aligned on the same plane of the substrate, resulting in a simultaneous dual-band control of the reflection direction up to ±30° independently. Furthermore, the dual band reflectarray showed higher transmittance at frequencies except for the target frequencies, indicating the reflectarray function only at 28 and 39GHz and does not interfere with the other communication bands.

A Polarization-Insensitive Dual-Band FSS With High Selectivity and Independently Switchable Characteristics

The investigation of dual-band frequency selective surface (FSS) has attracted a great deal of attention over the past few decades. However, the existing reconfigurable dual-band FSSs exhibit first-order responses with poor frequency selectivity. In this letter, a polarization-insensitive dual-band FSS with a rotationally symmetrical receiver–transmitter unit-cell configuration that exhibits a second-order response is presented. p-i-n diodes are loaded on separate layers to achieve the independent switching of two passbands. The full-wave simulation results are presented, and an equivalent circuits model is also presented to analyze the operation principle of the proposed FSS. The measurement results of our fabricated prototype indicate that the device exhibits two independently switchable polarization-insensitive transmission bands centered at 3.06 and 4.33 GHz. The shape factors representing the selectivity of the transmission band are 2.44 and 2.46, respectively, which are approximately 1/4–1/2 times that of the existing reconfigurable dual-band FSSs. The proposed FSS exhibits angular stability up to 40 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ }$</tex-math></inline-formula> below 5 GHz. This work paves the way toward high selectivity reconfigurable dual-band FSS.

Dual-Band Ultrathin Polarization Converter for S-Band Microwave Transmission

In this letter, a low-profile dual-band frequency selective surface (FSS) is designed as a polarizer for satellite communication. This single-layered FSS with a meandered open loop intersected by a metallic strip behaves as a dual sense polarizer. It converts linearly polarized (LP) EM waves of frequency range 2.01–2.64 GHz into left-hand circularly polarized (LHCP) EM waves. Similarly, the LP waves in the frequency range of 3.26–3.68 GHz are converted into right-hand circularly polarized (RHCP) EM waves. The unit cell dimension of the compact polarizer is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.075\lambda _{0} \times 0.075\lambda _{0} \times 0.005\lambda _{0}$ </tex-math></inline-formula> , where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{0}$ </tex-math></inline-formula> stands for free space wavelength at the lowest cut-off frequency. This study explores the structural design evolution of the proposed polarizer and verifies the frequency behavior of the structure using a circuit model. The simulated performance of the dual-band polarizer is experimentally tested. Good concordance is observed between the simulated and measured results.

Design of Dual-Band Frequency-Selective Surfaces With Independent Tunability

A design approach for dual-passband frequency-selective surface (FSS) with independent tunability is proposed and implemented. The principle of the proposed design approach is elaborated based on an equivalent circuit model, and it is demonstrated that the construction of FSS unit cell with two independently controlled transmission poles plays a decisive role. Referencing to the proposed approach, a varactor-based polarization-insensitive dual-passband FSS with independent tunability is demonstrated experimentally for the first time. In this prototype, a shunted substrate integrated waveguide cavity (SIWC) like structure is designed to realize electromagnetic isolation and serve as the dc ground for varactors to simplify the dc bias feed network. Simulated and measured results show that both passbands located in L-band and S-band can be tuned independently, and the transmission characteristic of the designed tunable FSS (TFSS) possesses good angle stability.

Arbitrary polygon shape optimization applied to multiband frequency selective surface inverse design

An arbitrary polygon shape optimization method is proposed for multiband frequency selective surface (FSS) inverse design in this paper. Different from the traditional deterministic methods, our approach uses the relationship between lumped parameter of equivalent circuit model (ECM) and distribution parameter which can readily determine the search direction. Meanwhile, the iteration step size is determined by the normalized current density. Polygon representation of FSS element can improve the degree of freedom of structural optimization to a great extent compare with parameterized method. This approach has the ability to avoid the conflict of multi-objective optimization and optimize multiband FSS effectively and accurately. A dual-band FSS is taken as a case to verify the method. The simulation results of optimized structure meet the expectation and are basically coincident with measurement results, thus verifying the feasibility of the optimization method.

Effectively Optimized Dual-band Frequency Selective Surface Design for GSM Shielding Applications

Nowadays, global system for mobile communication (GSM) systems are widely used. Therefore, the impact of mobile GSM signals on human health is one of the current research topics. Furthermore, electromagnetic interference caused by GSM signals can be a significant threat to electronic devices today. To overcome these problems, the surfaces of electronic equipment and exterior or interior walls of buildings can be covered with frequency selective surface (FSS) that stops unwanted GSM signals and passing the other signal. This work presents a novel dual-band FSS that attenuates the 900 MHz and 1800–2170 MHz GSM bands by at least 10 dB in the transmission direction. At the design stage, nested geometries are used to achieve multi-stop band frequency response. The proposed design is effectively optimized by utilizing the equivalent circuit geometries and current and electric field distribution diagrams. So, minimum of 10 dB attenuation is achieved in targeted GSM bands for all polarizations and up to 60 degrees (except TM 60 degrees) of incidence angles.

Design of Dual-Stopband FSS With Tightly Spaced Frequency Response Characteristics

This letter proposes a dual-stopband frequency selective surface (FSS) with tightly spaced frequency response characteristics. The metal layer of this FSS structure is composed of a metal strip of a bow-type ring and a metal strip of a square ring type, which forms the center symmetric ring structure. This dual-band FSS can achieve reflection characteristics at 6.29 and 8.35 GHz, which belong to C-band and X-band, respectively. In addition, two resonant frequencies can be independently controlled for good flexibility. This structure has excellent polarization stability and angular stability. Furthermore, a prototype sample of the proposed structure in this letter is processed and produced, and the test results are highly consistent with the simulation structure after being measured in a microwave anechoic chamber.

A miniaturized angularly stable dual‐band FSS based on convoluted structure and complementary coupling

A miniaturized dual-band frequency selective surface (FSS) with high angular stability is proposed. The unit cells of the proposed FSS have a convoluted pattern and hexagonal contour, which are arranged into array compactly. The FSS is implemented on single substrate with two metallic layers which has a low profile. The top and bottom patterns are complementary which generate two passbands separated by a transmission zero. A high out-of-band suppression is obtained, and the two bands can be tuned simply and flexibly. The FSS is highly stable with respect to different incident angles and polarizations due to the rotationally symmetric structure. An equivalent circuit model is developed, and a prototype working at 2.15 GHz and 3.8 GHz is fabricated, whose dimension is only 0.05λ0 at the lower band. The simulated results agree with measured results very well.

A Dual-Frequency Miniaturized Frequency Selective Surface Structure Suitable for Antenna Stealth

A tiny dual-band frequency selective surface structure is proposed in this paper. With dual-band rejection characteristics at the corresponding frequency points of the S-band and C-band, suitable for antenna stealth. To achieve miniaturization, the unit-cell architecture resembles the shape of a “S.” First of all, the author describes the parameters of the surface element, and then, the transmission characteristics of the surface element are analyzed by the equivalent circuit method. By maintaining a constant response to TE and TM polarization patterns and oblique incident angles, the suggested device ensures angular independence. The measured findings from the constructed FSS are used to validate the computed results. Finally, a new unit structure is provided for the application of FSS in antenna stealth.

Frequency selective surface based on Ti3C2Tx MXene for dual band Wi-Fi applications

A dual-band frequency selective surface (FSS) employing Ti3C2Tx deposited on a polyethylene terephthalate (PET) layer is proposed for Wi-Fi applications. The structure can afford dual-frequency passbands with central frequencies of 2.4 GHz and 5.5 GHz and realize large bandwidths covering 1.7-2.9 GHz and 4.9-6 GHz for -3 dB reference, which are bands of Wi-Fi communication. Featured by the use of 4.3 μm-thick Ti3C2Tx, the FSS reduces the thickness by 16% compared to that using 35 μm thick copper, which renders it preferable for flexible and ultrathin applications. Moreover, the proposed FSS has the advantages of polarization and incident-angle insensitivity as well as the ease of fabrication. The proposed FSS based on Ti3C2Tx MXene for the first time may provide a further step in the development of ultrathin, lightweight and flexible devices for wireless communication, such as filters, absorbers and modulators.

Dual-Band Single-Layer Fractal Frequency Selective Surface for 5G Applications

Due to the global growth in popularity of Fifth Generation (5G) cellular communications, the demand for shielding against it has risen for a variety of applications, mainly related to cybersecurity but also to isolation, calm areas and so on. This research paper aims to provide a suitable dual-band fractal FSS (Frequency Selective Surface) for the 5G lower band frequencies: 750 MHz and 3.5 GHz. The unit cell is in the shape of a bow tie, where each of the triangular parts are Sierpiński triangles. One major addition to the unit cell is a central metal strip to make the manufacturing of the FSS more feasible and to tune the operation frequencies and bandwidths. As with each different stage of a fractal antenna, the different stages of the fractal FSS design behave differently. For this application, stage 2 is sufficient, as we are able to cover frequency bands among those included in the FR1 5G spectrum. Some equations were derived using linear regression in order to provide specific design tools for building an FSS. These equations have high accuracy and can be used to adapt the proposed design to other frequencies. Some other parameters, which are not represented in the aforementioned equations, can also be adjusted for minor tweaking of the final design. This design performs well except under large incidence angles. This should be taken into account when proposing the installation of a structure based on it. A good agreement between simulation and measurement results is observed.

Design of miniaturized dual-band frequency selective surface with spiral arrangement of meander lines

Design of miniaturized dual-band frequency selective surface with spiral arrangement of meander lines

Metamaterial-inspired optically transparent active dual-band frequency selective surface with independent wideband tunability.

This paper presents an optically transparent active bandstop frequency selective surface (FSS) with wideband tunability of two resonance frequencies using the concept of miniaturized element FSS (MEFSS). The proposed design consists of metallic square loop arrays on a new optically transparent substrate as the top layer, a glass interlayer, and periodic patterns of cross dipoles on the substrate as the bottom layer. Two kinds of resonant elements loaded with varactors and the designed bias networks achieve two independent tunable stopbands. The proposed FSS has two large tuning ranges, one is from 1.20 GHz to 2.63 GHz and another is from 2.0 GHz to 5.9 GHz (75% and 99% with respect to the center frequency, respectively). The wideband dual-tuning mechanism is theoretically analyzed and demonstrated by deriving its equivalent circuit (EC) model. The experiment results exhibit reasonable agreement with the numerical simulation responses. This proposed design, with low profile, angular stability, polarization insensitivity, optical transparency, and wideband dual-tunability can play an important role in manipulating electromagnetic wave propagation for manifold applications.