A Miniaturized Dual-Band Frequency Selective Surface (FSS) With Closed Loop and Its Complementary Pattern

The miniaturized frequency selective surface (FSS) obtained by connecting a number of limbs with two flexible adjustable transmission zeros is proposed in this paper. The proposed FSS has two transmission zeros on both sides of the passband. The effects of the geometrical parameters on the bandwidth of transmission zeros and pole are analyzed. Adjusting the numbers of the limbs in the FSS can make a great difference to the ratio of the frequencies of the two working transmission zeros, and the coupling between the adjacent FSS unit cells is used to adjust the ratio of the frequencies of the two working transmission zeros slightly. The simulated results show that the ratio of the frequencies of the two working transmission zeros has wide adjustable range. The effects of the ways to connect the limbs on the ratio of the frequencies of the two working transmission zeros are analyzed. The prototype of the FSS with two limbs is fabricated and tested to verify the feasibility of the proposed method. The measured results show that the FSS designed by the proposed method has good polarization and angel stabilities, and this proves the proposed way is effective. This FSS is a good candidate to isolate the communication systems with two working bands.

A low-profile broadband bandpass frequency selective surface (FSS) with two rapid band edges is proposed in this paper for 5G near-field applications. The overall structure consists of three metallic layers, separated by two thin substrates with a thickness of 0.07λ. In addition, some centro-symmetric miniaturized slots are introduced in the middle metallic layer to further improve its stability and reduce its physical dimensions. A corresponding equivalent circuit model (ECM) is also proposed to better analyze the principles of the proposed FSS. Finally, an FSS prototype working at the center frequency of 27.5 GHz with a relative -3 dB bandwidth of 20.5% is fabricated and measured. More than 25 dB shielding effectiveness can be obtained out of the passband for a bandwidth of 1.46 GHz in this experiment. Both 3-D full-wave simulations and ECM results are in good agreement with the experimental results, having a maximum deviation of only 2.257% in the transmission zeros and poles. These results demonstrate that the proposed FSS is a good candidate for 5G near-field EMI shielding.

Single-layer dual-band frequency selective surface for coverage-enhancing applications in millimeter-wave 5G

In this paper, a low-profile tunable bandstop frequency selective surface (FSS) is presented for S-band applications. The FSS consists of square loops connected through varactor diodes across the diagonals. By controlling the reverse voltage of the varactors, the resonance frequency can be tuned for a wide frequency range. Full-wave simulation shows 21% tuning range from 2.31 GHz to 2.79 GHz with respect to lower resonance frequency. The novelty of the design lies in its four-fold symmetry, which makes the structure polarization-insensitive. The FSS is also angularly stable under oblique incidence for both TE and TM polarizations. Additionally, an equivalent circuit model has been introduced to explain the resonance mechanism of the proposed FSS. The structure is also fabricated and measured, where good agreement is observed between simulated and measured responses.

Purpose The purpose of this paper is to present the results of a particle swarm optimization (PSO) method applied in the design of a square-loop frequency selective surface (FSS) via the equivalent circuit model (ECM), considering the dielectric effective permittivity as a variable in the optimization problem. Design/methodology/approach In the optimization process considered, besides the FSS square loop geometric parameters, the thickness and relative permittivity of dielectric material used as support are included as variables in the search space, using for this a model of dielectric effective permittivity introduced by the authors in a previous work. Findings Square loops were designed and the obtained results were compared with designs reported in literature for applications in wireless local area network and long-term evolution 4G systems. The low computational cost is remarkable as well as the acceptable accuracy obtained with the proposed approach. The PSO method results were implemented with the ECM and compared with those obtained via Ansys – high frequency structure simulator commercial software simulations. Originality/value The lack of a model of dielectric effective permittivity for the ECM causes a restricted search space in the stochastic FSS design process limited to only geometric parameters, as it is reported in the available literature. The proposed approach simplifies and makes more flexible the design process, and allows guiding the FSS design to unit cell surface and/or dielectric thickness of small dimensions.

A method for designing miniaturized frequency selective surface (FSS) using equivalent circuit model (ECM) and multi-objective particle swarm optimization (MOPSO) algorithm is proposed in this paper. In the proposed method, ECM describing the desired frequency response is established, and parameters of the ECM are determined using the MOPSO algorithm. Combining the ECM analysis and the MOPSO algorithm, the requirements of desired frequency response can be converted into the constraints of equivalent circuit parameters, which simplifies the optimization process of FSS design. For verification, a single-layer bandstop-bandpass FSS composed of convoluted elements with the unit cell size of 0.073λ 0 × 0.073λ 0 is designed. Simulation results show that the −15 dB bandwidth is from 2.62 to 2.83 GHz, and the −0.5 dB bandwidth is from 3.84 to 5 GHz. Meanwhile, the resonant frequency is stable at different incident angles (up to 80°) under TE and TM polarization. Finally, the proposed FSS prototype is fabricated and measured. The measured results agree well with the simulated ones.

In this paper, a dual-band Frequency Selective Surface (FSS) absorber is presented for Wireless Local Area Network (WLAN) security. The FSS absorber is designed for two frequencies of interest, i.e., 2.45 GHz (lower band) and 5.25 GHz (upper band), respectively. FSS design consists of two layers; first layer consists of conducting square-loop elements while second layer consists of resistive square-loop elements, placed in-front of a conducting FSS layer. The proposed FSS design provides good frequency stability for oblique incidences for perpendicular (TE) and parallel (TM) polarizations. It provides better absorption rate for 2.45 GHz and 5.25 GHz frequency bands and allow the transmission of other microwave frequencies. Also, the proposed FSS design reduces multipath fading of additional WLAN signals which occurred due to the placement of conducting FSS layer. Presented results demonstrate that the proposed FSS design has a stable frequency response for the desired frequency bands for TE and TM polarizations with good absorption rate when the incident wave angle varied from 0<SUP>0</SUP> to 45<SUP>0</SUP>.

This paper proposes a fractal square loop frequency selective surface (FSS) with dual-band stop behavior. The FSS elements are etched on FR-4 substrate to attenuate signals at GSM900, GSM1800 and IMT2000 frequency bands while transmitting other microwave signals. The unit cell geometry is a modification of the conventional square loop which shows an improvement in stability for oblique incidence up to 45° for both TE and TM polarizations. The proposed FSS shifts the onset of a grating lobe to the outside of the frequency of interest without compromising the target resonant frequencies. The measured results are shown to be in a very good agreement with the simulated results.

A second-order bandpass frequency selective surface (FSS) for terahertz applications is experimentally demonstrated in this paper. The proposed FSS is designed using miniaturized element unit cells that enable analysis of their frequency by an equivalent circuit model. A transmission zero is introduced in the upper stopband of the transmission response for improving the out-of-band performance. Numerical and experimental results show a harmonic-free response up to three times the passband center frequency.

In this paper, a frequency selective surface (FSS) element has been presented based on substrate integrated waveguide (SIW) technology for improved EM performance. The SIW cavity results in the generation of additional resonance, which combines with the resonance of FSS shows a relatively wider bandwidth (BW). Furthermore, the FSS based on SIW exhibits a sharp roll-off performance with flat transmission characteristics. The FSS element is designed to operate in Ku-band near 15.0 GHz for satellite application. Two design examples have been reported for the dual band and broadband response. The estimated results have proven the superiority of the SIW cavity FSS over its conventional form.

A simple analysis technique for a concept in frequency selective surfaces (FSSs) basis from Babinet's principle, of two closely coupled conducting elements is presented. A layer of conducting patch elements and a layer of slot elements are designed on either side of a substrate, named as complementary FSS (CFSS). An equivalent circuit (EC) model in conjunction with transmission line (TL) model is employed to analyze the response of the structure. This method can predict the scattering parameters with high accuracy at a normal and oblique angle of incidence for both parallel and perpendicular polarizations. A parametric study of CFSS array aimed at their EC model optimization is presented. The CFSS exhibits a highly stable passband for normal and oblique incidences. The validity of the proposed method is verified with commercial simulation software package. It is observed that the results obtained by both methods are very good in agreement.

In the paper, a tri-band angularly stable frequency selective surface (FSS) with controllable resonances for electromagnetic shielding is proposed. Different from traditional single-layer structure, the FSS proposed is based on cascaded structure that creates three adjustable blocking bands around frequency 5.93 GHz, 7.33 GHz and 9.17 GHz, respectively. The designed FSS has a low profile with thickness of λ0/100, where the λ0 represents wavelength of the first band-stop resonance frequency. Besides, the proposed FSS exhibits stable frequency response up to 70° with respect to different polarizations. Therefore, this FSS is flexible and can be used in electromagnetic shielding field where needs conformal screen. To investigate and understand the operating mechanism better, a equivalent circuit model (ECM) is deduced and given in the Section 2, the calculated results match the full-wave EM simulation results perfectly. Finally, a prototype of this FSS is fabricated and measured, the measurement results are in accordance with the simulation results.

A novel bandpass frequency-selective surface (FSS) with high selectivity and angular stability is presented. In the skirts of the narrow passband, two transmission zeros (TZs) are generated, leading to the steep roll-offs at both left and right skirts. The realization of two TZs using a single piece of a printed circuit board facilitates the fabrication. The current distribution and equivalent circuit model are given to illustrate the generation mechanism of the TZs. The proposed FSS can achieve good stabilities of polarization and angle. The size of this FSS is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.15\lambda $ </tex-math></inline-formula> . The prototypes of the proposed FSS are fabricated, and good performance is obtained.

In this paper, a rectangular metallic ring FSS (Frequency Selective Surfaces) with parallel metallic strips for multi band applications are characterized by the WCIP (Wave Concept Iterative Procedure) method. The proposed FSS structures are made of metallic elements that are simultaneously independent in the spatial domain and uncoupled in the spectral domain. Thus the FSS multiband behavior can be achieved only by a building process based on independent metallic elements in both domains. The resonant characteristics of the proposed FSS are determined. The structure shows three resonant frequencies when the incident wave is x-polarized and three resonant frequencies when the source is polarized in the orthogonal direction. A variation in the length of the strips and the rectangular ring allows a fine tuning in the FSS resonant frequencies to give raise to tuned bandwidths. The suppression of a resonant frequency can be insured either by the elimination of the responsible metallic strip or by the insertion of a PIN diode switch. Three FSS structures are manufactured and characterized. The FSS bandwidth can be enhanced in both perpendicular FSS exciting source directions by only varying the strips lengths and the ring dimensions to the corresponding resonant frequencies. A good agreement is obtained when the WCIP results are compared with the simulations of COMSOL Multiphysics software and experiment.

In this article, a novel conformal frequency selective surface (FSS) with dual reflection bands located at X and Ku bands and a transmission window near 12 GHz is proposed, which brings little aberration in the far-field pattern. The unit cell consists of double flower-shaped strips on an ultrathin dielectric slab. The equivalent circuit model is established by the field distributions to illustrate the resonant mechanism, the parameters of which are calculated. The planar and elliptic cylindrical samples are fabricated and tested. The test results are consistent with simulation data. The two samples’ averages of shielding effectiveness are no less than 16 dB. The insertion losses of the planar and the curved FSS are less than 1 dB in the passband. The near-field distributions in three concerned bands are scanned. The conformal FSS excites slight distortion in the passband but stirs the distributions into a mess, the electric field intensity of which drops by 20 dB in the stopbands. Moreover, the absolute gains in the passband are tested in compact antenna test range. The far-field pattern is also evaluated by near-field to far-field method. The data obtained by two methods is consistent with the simulation. Little aberration by the FSS occurs in the passband, and the average gain's deviation is no more than 0.64 dB.