Dual-band Frequency Selective Surface Research Articles

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.

Miniaturized dual stop band frequency selective surface with broadband linear co to cross polarization conversion ability

This work presents a miniaturized angularly stable frequency selective surface (FSS) on a single layer substrate. Unit cell comprises of convoluted circular rings connected cross dipole and linear arrow headed dipole printed on both sides of the substrate. A closely spaced dual stop band resonances are obtained at 10 and 14.3 GHz with frequency ratio of 1.43. FSS shows a − 10 dB stopband bandwidth (BW) from 7.32 to 11.05 GHz (40.61%) and 12.68 to 15.97 GHz (22.97%) with >30 dB stop band rejection at center frequencies. FSS poses the features of stable performance under change in polarization and angularly stable response up to 60° incident angle. Later the proposed FSS is printed on grounded thick dielectric substrate and it shows broadband reflection type co to cross polarization conversion from 7.2 to 17.32 GHz (82.54%) with polarization conversion ratio >80% and oblique angle stability up to 35°. To the best of authors' knowledge, this is the first time in literature a single unit cell geometry with two different properties, spatial filtering on transmission and polarization conversion on reflection have been designed and analyzed in details. A finite array with size 25 × 25 of the proposed FSS is fabricated and the measured filter response shows a good agreement with simulated performance at normal and oblique incidences. The proposed FSS is used as a reflector of a dual band monopole antenna and the simulation results shows gain improvement of 5.51 and 3.8 dB at the two stopband frequencies.

Gain augmentation of a dual‐band dielectric resonator antenna with frequency selective surface superstrate

Gain augmentation of a dual-band antenna with different bandwidths using superstrate is presented in this paper. Initially, the dual-band radiator is designed using a rectangular dielectric resonator (DR). The fundamental mode TE111 of the rectangular DR resonates at 3 GHz over a narrowband (BW = 5.08%). The upper wideband (BW = 20% with center frequency 5.86 GHz) is obtained by the amalgamation of two hybrid modes with higher-order TE113 mode. The dielectric waveguide model is used for the theoretical analysis of two radiating modes of the rectangular DR. Further, a dual-band frequency selective surface with bandpass response is designed and loaded as a superstrate above the DR antenna for gain improvement in both the bands, which leads to a gain augmentation of 1.8 dBi and upto 3.5 dBi in the lower and upper band respectively. At last, the proposed design is implemented practically, and measurement results are portrayed to compare with simulation results that agree reasonably well.

A frequency selective surface with 3-D unit cells

This paper conceptualizes the development of a frequency selective surface (FSS) with 3-D unit cells. The FSS unit cells individually present a three-dimensional structure, whereas collectively these are more like planar FSS. The unit cell substrate has been printed using 3-D printing technique and metallized using copper paint. The 3-D printing offers a degree of freedom to fabricate substrate material in three dimensions. Various designs of unit cell have been studied by fabricating a dual-band FSS which highlights the significance of the dimensional change of the 3-D unit cell over FSS performance. The designed FSS has been fabricated and tested using VNA where test results are found as per desire. The main objective of the paper is to develop a comprehensive method for rapid prototyping of FSS in applications in the area of radar, satellite and navigation.

Miniature Convoluted FSS for Gain Enhancement of a Multiband Antenna

Convoluted elements on a frequency selective surface (FSS) allow for low frequency elements to be contained in physically smaller unit cells. Smaller unit cells give the FSS greater angular stability, especially where a curved FSS is required, and so unwanted grating effects are avoided. A convoluted element FSS with a frequency rejection band centred at 2 GHz and unit cell area of 15 mm by 15 mm ( $0.10\,\,\lambda \times 0.10\,\,\lambda$ ) has been developed. To test its usefulness, the full structure FSS is used as a parabolic reflector in a dual band FSS reflector antenna operating at 1 GHz and 2 GHz. Simulated and measured results are close at both bands. The reflector antenna has high gain at 2 GHz of 12.7 dBi (simulated) and 11.7 dBi (measured). To observe the angular stability of the FSS and therefore its effectiveness as a reflector, it was compared with a copper test reflector at both bands. Simulation of the reflector antenna with test reflector produced a 2 GHz gain of 13.3 dBi which is very close to that with the FSS reflector. The simulated 2 GHz gain plot of the reflector antenna with FSS reflector is very similar to that with the test reflector indicating that the FSS has good angular stability. The gain at 1 GHz is also high with 9.3 dBi (simulated) and 8.7 dBi (measured). Simulation of the reflector antenna with no FSS and only a rear test reflector produced a 1 GHz gain of 10 dBi which is very close to that with the FSS reflector in place indicating that the FSS causes no significant attenuation at that frequency. The convoluted element FSS would be useful as a curved reflector in the creation of high gain, multiband, conformal antennas.

Miniaturized Angularly Stable Dual Band Frequency Selective Surface for K and Ka Band

A single layer novel compact frequency selective surface which is used in reflector antenna is designed and simulated. The proposed unit cell reflects electromagnetic waves in K and Ka band with maximum reflection occurring at 22.62 GHz and 35.44 GHz respectively. The designed FSS find its application in satellite communication. A crossed dipole structure in center and two-legged structure in corners with square loop in each quadrant makes the FSS unit cell structure. The FSS is designed with oblique incidence for transverse electric and transverse magnetic polarization with return loss 0.3 dB in 22.62 GHz and less than 0.5 dB in 35.44 GHz. The proposed work shows frequency independence against oblique angle of incidence. The simulated result from CST microwave studio is compared with other similar works.

A miniaturized flexible frequency selective surface for dual band response

AbstractIn this paper, a novel miniaturized and flexible dual band frequency selective surface (FSS) is presented. This FSS provides effective shielding in X-band and Ku- band, with a frequency response of 9.4 and 16.7 GHz, respectively. The proposed FSS provides 924 MHz bandwidth at X-band and 1.34 GHz bandwidth at Ku-band with an insertion loss of 20 dB. Moreover, the proposed design is polarization-independent and it provides stable frequency response at various angles of incidences for both transverse electric and transverse magnetic modes. More significantly, the proposed FSS analyzed the bandstop response of the selective frequency and also is suitable for conformal applications. A prototype of the proposed FSS is fabricated. The measured results and simulated results are good in agreement.

Miniaturized Dual-Band FSS Suitable for Curved Surface Application

Based on a single metallic layer printed circuit board (PCB), a miniaturized dual-band frequency selective surface (FSS) is proposed that could fulfill thin substrate design for curved application and provide stable resonant frequency. Due to the property that the element size can be altered by using different thicknesses of substrate, the FSS could either be designed for the compact size or in a very thin substrate. Two practical designs for dual-band wireless local area network (WLAN) are demonstrated featuring a flexible and straightforward design method. The compact one has an element size of only 5.2% of the free space wavelength at the lower resonant frequency, which is the smallest dual-band WLAN FSS by using only one metallic layer in published literature. Another thin substrate design (0.4 mm PCB) is fabricated and measured to confirm that the FSS exhibits stable resonant frequency on curved surfaces with different curvatures. The measured frequency shift is only 2.2%, which is among the smallest percentage in the literature.

Transforming single-band static FSS to dual-band dynamic FSS using origami

Frequency selective surfaces (FSSs) have been used to control and shape electromagnetic waves. Previous design approaches use complex geometries that are challenging to implement. With the purpose to transform electromagnetic waves, we morph the shapes of FSS designs based on origami patterns to attain new degrees of freedom and achieve enhanced electromagnetic performance. Specifically, using origami patterns with strongly coupled electromagnetic resonators, we transform a single-band FSS to a dual-band FSS. We explain this transformation by showing that both symmetric and anti-symmetric modes are excited due to the strong coupling and suitable orientation of the elements. Also, our origami FSS can fold/unfold thereby tuning (i.e., reconfiguring) its dual-band performance. Therefore, the proposed FSS is a dynamic reconfigurable electromagnetic structure whereas traditional FSSs are static and cannot change their performance.

Dual-Band Frequency Selective Surface Based on Shunted SIW Cavity Technology

The design of a hybrid frequency selective surface (FSS) is presented based on the substrate integrated waveguide cavity (SIWC) technology. The intended design combines two FSS slots (multiapertures) based on the SIWC by sharing the adjacent vias of the unit cell to exhibit unique features in terms of their cavity designs and performance. The design consists of a circular slot with a circular cavity (named as Cavity-A) and a cross slot with a shared cavity with an adjacent unit cell (named as Cavity-B). As a result, the structure shows the dual-bandpass response with sharp roll-off performance characteristics. One band possesses narrowband characteristics at 8.12 GHz. Whereas, the next band with wide bandpass characteristics from 9.5 to 11.5 GHz. Further, the structure has shown a very low insertion loss (IL) of better than 0.15 dB in its operating bands. For proving the concept, a physical prototype has been fabricated, and its functionality verified. A good agreement has been found between the estimated and experimental results.

Dual-Band Frequency Selective Surface With Compact Dimension and Low Frequency Ratio

In this paper, frequency selective surface (FSS) with low profile, miniaturized structure and closely located dual-band is proposed based on the fractal technology. The FSS is designed by etching the conductive pattern on a single layer substrate. Two fractal slots are designed to increase the spatial efficiency of the pattern and provide two isolated resonances. For the dual-band FSS, the miniaturization should work for both of the resonances to keep the frequency ratio. Therefore, the slots are convoluted as different principles and twisted with each other to keep the miniaturization and isolation. With the third-order fractal pattern, two pass-bands are achieved at 1.04 GHz and 1.49 GHz with the frequency ratio of 1.42. The dimension of the element is as compact as 0.039λ× 0.039λ where λ is the wavelength of low frequency resonance. Moreover, benefiting from the miniaturized element, the angular stability is very good that the resonances keep stable when the incident angle increasing from 0° to 60°. In order to get insight of the mechanism of the proposed element, an equivalent circuit model is established and studied. A prototype is fabricated and all the proposed performances are verified by simulations and measurements.

S/X dual-band real-time modulated frequency selective surface based absorber

Frequency selective surface (FSS) is of great research interest for its wide applications in radome, absorber, electromagnetic filters, and artificial electromagnetic bandgap materials. In order to achieve a multifunctional FSS with real-time manipulated radar cross-section (RCS), there are mainly three ways, i.e. to design reconfigurable FSS unit cell, reconfigurable screen, and a combination of reconfigurable unit cell and screen. In this work, a combination design of both the reconfigurable unit cells and FSS screen is proposed to realize a dual-band FSS absorber with real-time manipulated RCS. For the reconfigurable unit cell, an angular ring and a meander cross dipole are combined to obtain a dual-band absorption. The dual-band resonance frequencies are reconfigurable by switching the PIN diodes embedded in the unit cell. When switching the PIN diodes, the resonance frequencies of the unit cell would be changed due to the variation of the effective capacitance and inductance of the unit cell. For the reconfigurable FSS screen, a novel biasing network is introduced, then the scattering field from each unit cell is modulated independently by switching the “on/off” state of the PIN diode through using a programmable field programmable gate array (FPGA). The total scattering far field is expressed as the superposition of the scattering field from each unit cell, and the far field scattered by the unit cell which is evaluated under an infinite periodic boundary condition. The scattering field of the FSS absorber can be predicted by considering the working states of all the unit cells on the screen. We define the unit cell as state “0”, when all the PIN diodes are at the states of “off”, and as state “1” when the PIN diodes are all at the states of “off”. The entire screen of FSS absorber is thus pixelated, which can be expressed by a binary coding matrix. The real-time scattering fields from the FSS absorber are manipulated perfectly by optimizing the states matrices showing “on/off” of each unit cell with genetic algorithm (GA). The FSS absorber is fabricated and measured. The ranges of 33dB and 25dB reconfigurable monostatic RCS at 3.2 GHz and 10.3 GHz are achieved by coding the states of unit cells on the FSS absorber screen. Both full-wave and analytical simulations demonstrate the effectiveness of the proposed optimization procedure. Compared with the reported FSS absorber, the proposed design is validated to possess good performance.

Dual-Band Frequency Selective Surface on Aperture-Coupled Patch Resonators With Different Polarization Rotation

In this letter, a dual-band frequency selective surface (FSS) based on aperture-coupled patch resonators is proposed to achieve different angles of polarization rotation, that is, 90° and 0°. The dual-band response is achieved by periodically arranging two independent subelements consisting of back-to-back patch resonators with coupling apertures etched on the middle metallic layer. Herein, the first passband is realized by the crossed patch resonators with a pair of rectangular apertures etched beneath the edges of the crossed patches. It can produce 180° phase difference between the two orthogonal components of a linearly polarized incident wave oriented to the diagonal of the FSS elements, thus rotating the incident polarization to its orthogonal one in this first passband. The second passband is caused by the square patch resonators with crossed apertures etched beneath the center of the square patches, thereby maintaining the incident polarization unchanged in this second passband. The operation principle is, then, extensively analyzed and discussed. To validate the design concept, the proposed FSS is designed, fabricated, and measured. A good agreement between the measured and simulated results is achieved to reveal the attractive dual-band and dual-polarization features of the proposed FSS.

Design of Dual-Band Frequency-Selective Rasorber

A novel frequency-selective rasorber (FSR) with dual-band transmission and wideband absorption property is proposed in this letter. The FSR is a two-layer structure composed of a lossy resistive sheet at the top and a lossless bandpass frequency-selective surface (FSS) at the bottom, separated by an air spacer. The element of the resistive sheet is a lumped-resistor-loaded metallic dipole with a dual-resonance structure inserted in the center. The dual-resonance structure is realized by three different series LC structures in parallel, based on the Foster reactance theorem. There are two impedance poles between the three impedance zeros of the series LC circuits, where two transparent windows can be obtained for the lossy resistive sheet. The bandpass FSS is a simple dual-band FSS by etching two slots with different shapes and dimensions in a metallic plane. The FSR has realized two transmission bands at 7.7 and 12.6 GHz, and the band with | S 11| < −10 dB is 3.7–11.1 GHz. The design has been validated by full-wave simulation and experimental measurement.

Multi-Semicircle-Based Single- and Dual-Band Frequency-Selective Surfaces: Achieving Narrower Bandwidth and Improved Oblique Incidence Angular Stability

This article proposes two new frequency-selective surface (FSS) designs based on specific combinations of a multiple number of semicircles. One of the proposed designs makes use of four semicircles, yielding a single-band frequency response. The other consists of a combination of eight semicircles arranged in a square-like shape, producing a dual-band frequency response. The proposed designs were simulated with commercial electromagnetic simulation software.

Polarization Insensitive Dual Band Frequency Selective Surface for RF Shielding Through Glass Windows

This paper reports on a dual-band, polarization-insensitive frequency-selective surface (FSS) directly realized on window glass for Wi-Fi and WLAN shielding applications. The design incorporates an annular ring and modified flower-shaped geometry to suppress 2.45 and 5.5 GHz bands, respectively, while acting ineffective to the rest of the frequency spectrum. The proposed design is completely insensitive to incoming wave polarization owing to its symmetry. The FSS also offers excellent incident wave angular stability up to 45°. Additionally, a wide rejection bandwidth (−10 dB) of more than 630 and 1430 MHz for lower and higher bands, respectively, is obtained suffice to cover the WLAN spectrum. Unlike conventional screen-printed FSS for glass applications, the conducting patterns of the proposed FSS are realized with copper foil directly laminated and etched on the glass substrate while maintaining 86% transparency for sufficient light passage. The detailed analysis of all parameters has been carried out, and their effect on the performance of FSS is reported. An equivalent lumped circuit model is also generated for the proposed design to better understand the physical phenomena of electromagnetic (EM) wave suppression. A finite prototype containing 13 × 10 elements is fabricated and tested. The measured results are in good agreement with the simulated ones. The FSS offers measured suppression of 43 and 40 dB at 2.45 and 5.5 GHz bands, respectively. The design has excellent potential for EM field suppression, WLAN isolation, and security applications in indoor environments.

Spurious-Free Dual-Band Bandpass Frequency-Selective Surfaces With Large Band Ratio

Frequency-selective surfaces (FSSs) are widely employed in antenna's radar cross-sectional reduction, which plays a key role in improving survivability and penetration ability of future military systems. In practical, dual-band bandpass FSSs with large band ratio (BR) are urgently needed for some military equipment, such as homing head, that can detect both middle and far range targets. In this paper, a novel method for designing dual-band bandpass FSS with large BR is proposed. The method can provide a large BR response, by utilizing a spurious-free structure and combing resonant and nonresonant elements. The detailed analysis is presented with the aid of equivalent circuit model as well as closed-form equations to reveal the operating mechanism. A design example is simulated, fabricated, and then measured. Two excellent passbands are obtained with a large BR value of 15.3 in experiment. Moreover, a -10 dB fractional bandwidth of 164.3% is realized from 1.31 to 13.35 GHz, without observing any spurious transmission windows. In conclusion, our proposed method fills the gap of the existing dual-band FSSs to obtain a large BR value of more than 6 and could be a good guidance for designing the future multiband FSSs.

A compact angularly‐stable frequency selective surface for GSM 900/1800‐MHz shielding using cascaded 2.5‐dimension structure

In this article, a novel compact dual-band frequency selective surface (FSS) with stable response is proposed for GSM shielding. This FSS is designed using 2-layer cascaded 2.5-dimension structure of which element is composed of two via-based modified swastika unit cells. The proposed structure has created two stop bands around frequency 900 and 1800 MHz, respectively, with maximum attenuation value close to 70 dB. Besides, this FSS performs an excellent miniaturization characteristic with overall size of 0.048λ0 × 0.048λ0, where the λ0 represents the free space wavelength of the lower resonance frequency. More important, this FSS exhibits a very stable frequency response up to 80° for TE and TM polarization. To understand the structure better, the design procedure of this FSS is introduced in detail. Since the proposed FSS has an excellent comprehensive performance, this FSS has great potential in shielding GSM signal for small electronic devices. Finally, a prototype of proposed FSS is fabricated and measured. The measurement results prove the validity of simulation results.