Characteristics Of Frequency Selective Surface Research Articles

Wideband Polarization Rotation Transmitarray Using Arrow-Shaped FSS at W-Band

Based on the passband characteristics of frequency selective surface (FSS), a wideband transmitarray (TA) with linear polarization rotation at W-band is proposed. The middle layer of the unit cell is a pattern of arrow-shaped structure, which can rotate the incoming wave by 90°. A pair of parallel strip polarizers is employed to enhance the polarization conversion efficiency. The prototype of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$25\times 25$ </tex-math></inline-formula> -element TA is fabricated by the standard PCB technology. Within the 3 dB gain bandwidth of 20%, the measured peak gain of 28.7 dB with the corresponding aperture efficiency of 38.2% is achieved. The error analysis is also conducted by comparing the simulation and measurement. The performance of the proposed TA demonstrates that it is a suitable solution for wideband and low-cost applications in the millimeter-wave spectrum.

Design of frequency selective surface comprising of dipoles using artificial neural network

&lt;span&gt;This paper depicts the design of Frequency Selective Surface (FSS) comprising of dipoles using Artificial Neural Network (ANN). It has been observed that with the change of the dimensions and periodicity of FSS, the resonating frequency of the FSS changes. This change in resonating frequency has been studied and investigated using simulation software. The simulated data were used to train the proposed ANN models. The trained ANN models are found to predict the FSS characteristics precisely with negligible error. Compared to traditional EM simulation softwares (like ANSOFT Designer), the proposed technique using ANN models is found to significantly reduce the FSS design complexity and computational time. The FSS simulations were made using ANSOFT Designer v2 software and the neural network was designed using MATLAB software.&lt;/span&gt;

Study on Tunable Magnetized Plasma Frequency Selective Surface Using JEC-FDTD Method

The tunability of traditional frequency selective surfaces (FSSs) is inconvenient using metal material patch as periodic element, utilizing genetic algorithms to model FSS layers obtaining desired filtering electromagnetic waves effect. However, plasma tube is used as an element of the frequency selection surfaces substituting traditional metal patch in this article. A 3-D finite-difference time-domain (FDTD) formulation for dispersive media called the JE convolution (JEC) method is derived using the convolution relationship between the current density $J$ and the electric field $E$ to simulate the interaction of incident wave and magnetized plasma FSS. Numerical experimental results show that the electron number density of magnetized plasma has a significant effect on the resonance frequency, which can be modulated to the desired filtering by varying the density in the magnetized plasma elements. Whereas the magnetized plasma FSSs behave exactly like a perfect electric conductor (PEC) increasing the electron number density to a certain degree. Thus, modulation based on the ionized electron number density of the magnetized plasma can be designed into a tunable plasma FSS. Both the collision model and the noncollision model of the magnetized plasma are proposed to research electromagnetic transmission characteristics of FSS. It shows that the collision frequency only affects the reflectivity while has no effect on the resonance frequency in the following numerical experiments. In addition, magnetization intensity of the plasma FSS is also taken into consideration. The users obtaining the desired resonance frequency and transmission characteristics of plasma FSS by simply tuning the plasma’s electron number density, collision frequency, and magnetization intensity. So the magnetized plasma FSS can not only improve the electromagnetic shielding effect but also facilitate the modulation and rapid response to achieve the desired filtering effect. What is more, the magnetized plasma FSS can be turned off to achieve transparency, which greatly expands the universality of magnetized plasma FSS.

A High-Gain Filtering Antenna Based on Folded Reflectarray Antenna and Polarization-Sensitive Frequency Selective Surface

In this letter, the concept of high-gain multifunctional antenna based on folded reflectarray antenna (FRA) and polarization-sensitive frequency selective surface (FSS) is proposed. Antenna with multiple functions can be realized by using a polarization-sensitive FSS as the subreflector of FRA instead of the traditional polarizing grid. To validate this concept, a high-gain filtering antenna designed at Ka-band is presented as a design example. Good filtering performance of the antenna has been achieved due to the frequency selective characteristics of FSS. Besides, the relationship between the focal-length-to-diameter (F/D) ratio of FRA and the size of FSS element has also been discussed.

A low RCS wideband high gain CP slot antenna loaded with frequency selective surface

ABSTRACTIn this paper, a compact wideband circularly polarized slot antenna consisting of two L-shaped resonators is proposed. The slot antenna is loaded with a band-stop frequency selective surface (FSS) reflector to improve the gain of the antenna and to reduce the profile of the antenna. The radiation and scattering characteristics of FSS loaded slot antenna are compared with the metallic reflector loaded slot antenna, and the proposed antenna shows improved impedance bandwidth of 1.75–2.65 GHz. The measured results show that the peak gain of the slot antenna with FSS is enhanced by 4 dB. The proposed antenna with FSS also exhibits 3-dB ARBW of 2.2–2.65 GHz, and the scattering performance shows an average RCS reduction of 7.34 dB is achieved by slot antenna with FSS as compared to slot antenna with metallic reflector with peak RCS reduction of 24 dB at 1.2 GHz.

Reflection and transmission characteristics of frequency selective surface embedded within a thick plasma layer

In this paper, the reflection and transmission characteristics of frequency selective surface (FSS) embedded within a thick plasma is studied. The plasma layer is lossy and dispersive medium and the embedding of the FSS will change the electromagnetic wave propagation very much. The reflection and transmission coefficients of a square patch FSS layer embedding in plasma is calculated utilizing finite-difference time-domain (FDTD) method. Auxiliary differential equation (ADE) is utilized to simulate the dispersion of the plasma. The influence of the plasma and slab's parameter to the reflection and transmission coefficients is investigated. Various parameters of collision frequency, plasma frequency and thickness of plasma are involved to study the influence of these factors. The reflection and transmission coefficient values of different parameters are plotted to compare their effects. The results show that collision frequency reduces the reflection and transmission coefficient. Plasma frequency changes the FSS from low pass filter to band pass filter. Thick plasma slab makes the transmission coefficient oscillate as the variation of incident frequency.

Passive sensor frequency selective surface for structural health monitoring

Structural health monitoring (SHM) technologies have attained attention to monitor civil structures. SHM sensor systems have been used in various civil structures such as bridges, buildings, tunnels and so on. However the previous sensor for SHM is wired and encounter with problem to cover large areas. Therefore, wireless sensor was introduced for SHM to reduce network connecting problem. Wireless sensors for Structural Health monitoring are new technology and have many advantages to overcome the drawback of conventional and wired sensor. This project proposed passive wireless SHM sensor using frequency selective surface (FSS) as an alternative to conventional sensors. The electromagnetic wave characteristic of FSS will change by geometrical changes of FSS due to mechanical strain or structural failure. The changes feature is used as a sensing function without any connecting wires. Two type of design which are circular ring and square loop along with the transmission and reflection characteristics of SHM using FSS were discussed in this project. A simulation process has shown that incident angle characteristics can be use as a data for SHM application.

Tunability Study of Plasma Frequency Selective Surface Based on FDTD

This paper is focused on using plasma as element of a frequency selective surface (FSS). FSSs have been used for filtering electromagnetic waves for many years. Conventional FSSs use metal patch pattern as periodic element. This paper takes the plasma tube as a substitution for metal patch. The 3-D finite-difference time-domain method with periodic boundary condition is utilized to simulate the interaction of incident wave and plasma FSS. Numerical calculation results in that electron number density of plasma can dominate the resonance frequency obviously. The resonance frequency increases as the increasing of electron number density of plasma to the limit of that of perfectly electric conductor. Thus, the FSS can be designed to be tunable by changing the ionized electron number density. Both of the noncollision and collisional plasma model are introduced to study the FSS characteristics. The numerical calculation results show that the collision frequency only influences the reflectivity while has no effect on the resonant frequency. The resonant frequency and transmitted power ratio can be tuned by assigning the plasma’s electron number density and collision frequency. Thus, plasma elements offer the possibility of improved shielding effect along with reconfigurability. Plasma FSS can also be made transparent by tuning the plasma off which makes the use of FSS more versatile.

Dual mode modified double square ring resonator structure at 76 GHz

AbstractDual mode modified double square ring resonator (MDSRR) operating at 76 GHz millimeter‐wave has been simulated, and experimentally verified. MDSRR structure operates in two modes, metamaterial (MTM) mode and frequency selective surface (FSS) mode, depending on the direction of the electric field. The MDSRR in the MTM mode performs well at the desired frequency region by providing the highest insertion loss, S21, as reported in the literature with a loss of −0.5 dB. The electromagnetically induced transparency principle is applied to explain the loss reduction mechanism. The low losses MTM structure has the potential to enhance the performance of the radiating elements of the automotive radar systems. Conversely, in the FSS mode, the FSS characteristics of the proposed structure are numerically simulated and verified experimentally by changing the direction of the electric field along the x‐direction, in which the structure shows opposite behavior compared to the MTM performance. To demonstrate the validity of the FSS characteristics, the MDSRRs structure was tested using a waveguide measurement facility. The experiment results match well with that of the simulation, and wideband‐stop characteristics are introduced in the range of 74 GHz to 80.3 GHz.

Frequency Selective Surface for Structural Health Monitoring

Structural health monitoring (SHM) technologies have attained attention to monitor civil structures. SHM sensor systems have been used in various civil structures such as bridges, buildings, tunnels and so on. However the previous sensor for SHM is wired and encounter with problem to cover large areas. Therefore, wireless sensor was introduced for SHM to reduce network connecting problem. Wireless sensors for Structural Health monitoring are new technology and have many advantages to overcome the drawback of conventional and wired sensor. This project proposed passive wireless SHM sensor using frequency selective surface (FSS) as an alternative to conventional sensors. The electromagnetic wave characteristic of FSS will change by geometrical changes of FSS due to mechanical strain or structural failure. The changes feature is used as a sensing function without any connecting wires. Two type of design which are circular ring and square loop along with the transmission and reflection characteristics of SHM using FSS were discussed in this project. A simulation process has shown that incident angle characteristics can be use as a data for SHM application.

Residual stress and electromagnetic characteristics in loop type frequency selective surface embedded hybrid structures

Residual stresses occur in frequency-selective surface (FSS)-embedded composite structures after co-curing due to differences between the coefficients of thermal expansion between composite skins and FSSs. Furthermore, the electromagnetic characteristics may be affected by the deformation of the FSS pattern by residual stresses. Therefore, we studied the changes in electromagnetic characteristics due to the deformation of FSS, using residual stresses to deform loop-type FSS-embedded hybrid composites. We considered the effects of loop-type FSS patterns of equal dimension as well as the stacking sequences of composite laminates on the electromagnetic characteristics of FSSs: Square loop, triangular loop and circular loop. The stacking sequences of composite laminates considered in this study were [0]8, [0/90]4, [±45]4 and [0/±45/90]2. The FSS was located between composite laminates in the middle plane. To determine the residual stresses and deformations in the FSS embedded laminate structures, the thermal loading condition in the finite element analysis was induced by cooling the hybrid structures from 125°C to 20°C based on the cure cycle of the composite. Also, the electromagnetic reflection characteristics of the hybrid structures were predicted using deformed models by residual stresses, considering the effects of stacking sequence of composite laminates. The results showed that the maximum residual stresses and deformations were produced in the [0]8 composites with all three loop-types of FSS pattern. However, the maximum resonance frequency shifts occurred in the square and triangle loop-types with stacking sequence of [0]8, while the maximum resonance frequency shift occurred in the circular loop-type with stacking sequence of [0/±45/90]2.

Scattering characteristics of FSSs with triangular conducting elements

In this paper, scattering characteristics of dielectric backed frequency selective surfaces (FSSs) having triangular conducting elements are investigated for both transverse magnetic and transverse electric incident plane waves. Since triangular conducting elements are etched periodically on such a surface, incident and scattered fields are expressed as Floquet modes. Using Floquet’s theorem and satisfying the required boundary conditions an integral equation is obtained for the induced current density on the surface of a triangular conducting element in one periodic cell. This induced current density is expressed as a finite sum of piecewise triangular basis functions having unknown coefficients. The resulting integral equation is then converted to a linear matrix equation by using the Method of Moments. Taking the inverse transform of the matrix equation yields the unknown current coefficients which are finally used to compute the reflection and transmission coefficients. Since there are no theoretical or experimental results for FSSs comprising of triangular conductors, verification of the algorithm developed is carried out by comparing the numerical results obtained using this algorithm with the experimental and theoretical results in the literature for FSSs composed of strips and L-shaped conductors. For this, in the algorithm, appropriate arms of the triangles are removed to conform them into strips or L-shaped conductors. Results obtained for strips and L-shaped apertures by using this algorithm are in excellent agreement with the results in the literature.

The influence of dielectric truss on transmission characteristics of frequency selective surface

In order to analyze the influence of dielectric truss structure on frequency selective surfaces (FSS) transmission characteristics, as an example, the FSS of Y ring unit and the truss made of polyimide are investigated by the finite difference time domain method. The relevant physical model is developed and pore blocking rate is defined. Through the analysis it is proved that the variations of truss period and rib width will affect the FSS, so they become the main parameters to measure dielectric truss structure, and that the improvement of the aperture stop ratio will increase transmission loss. When truss period changes from infinity to 80 mm the transmittance of passband is reduced by more than 0.9 dB on an average; when the ribs width increases from 0 to 10 mm, the transmittance of passband is reduced by more than 0.6 dB on an average. When aperture stop ratio is lower than 12.11%, the passband produces no shipt. When aperture stop ratio is less than 4.12%, the influence of the truss on FSS is negligible. The FSS specimens is fabricated by coating and lithography process, the dielectric truss is machined by numerically controlled machine, and the microwave measurement is carried out in a dark room. The experimental results and the calculation results are verified to be in good agreement with each other. Therefore the present study presents an experimental and theoretical reference for designing the FSS stealth radar with the dielectric truss structure.

Simple prediction of FSS radome transmission characteristics using an FSS equivalent circuit model

We propose a simple method for predicting the characteristics of Frequency Selective Surface (FSS) radome using an equivalent circuit model. The required material properties, such as the permittivity and permeability of the FSS, were extracted from a FSS equivalent circuit model using a transmission and reflection method. These parameters were then used to calculate the transmission characteristics of FSS radome. We designed a sandwich radome using a square loop FSS for a 23GHz band application. In order to demonstrate the validity of our approach, we also performed a simulation to obtain the characteristics of the FSS radome using commercial full-wave software. The results from the two approaches are in good agreement. The method proposed herein could be used for the simple and rapid calculation of the design and fabrication of a FSS radome. The FSS radome is that a square loop FSS that has a stop band at 23GHz is insulated between two dielectric materials. A simple analysis of a FSS radome requires the material constants, the permittivity and permeability of the square loop FSS, which we extracted using transmission/reflection. Using the material constants derived from a FSS equivalent circuit model, the characteristics of the FSS radome were calculated for a simple 2-D case. The results were verified using a commercial full-wave three-dimensional electromagnetic wave simulator. The resulting characteristics of the FSS radome agreed with those obtained using a full-wave simulation. We show herein that the characteristics of a FSS radome can be analyzed and predicted with relative ease using an approximate FSS to achieve a simple 2-D construction. Our method can be applied to the analysis of FSS radome for use with various communication systems and electrical instruments.

RESONANT CHARACTERISTICS OF FREQUENCY SELECTIVE SURFACES ON FERRITE SUBSTRATES

The resonant characteristics of frequency selective surfaces (FSSs) on in-plane biased ferrite substrates for the TE polarization are described. An approximate formula for evaluating the resonant frequency is presented. The tunable property of the resonant frequency of a dipole FSS is flrstly demonstrated by the results obtained from the moment method (MM) and the waveguide simulator measurement. Then the approximate formula is validated by the MM as well as measured results already published in a previous paper. It is interesting to note that two separate resonances occur at any magnetic bias fleld, and both increase as the magnetic bias fleld increases. The fractional tuning range is investigated based on the approximate formula. The results show that it increases as the saturation magnetization increases and decreases as the center frequency increases.

Improvement of Bonding Characteristics Between the Frequency Selective Surface and E-Glass/Epoxy Composites for Stealth Radomes

Radomes of weapon systems such as aircraft, warships, and missiles have been manufactured using FSS (Frequency Selective Surface) for the stealth performance and E-glass/epoxy composite to protect the radar antenna from weather and mechanical impact and to minimize the loss of EM (electromagnetic) waves transmitted through the radome. In this work, the FSS was manufactured from an FCCL (Flexible Copper Clad Laminate) composed of a copper foil of 20 μm thickness and a polyimide film of 40 μm thickness. The bonding characteristics between the FSS and E-glass/epoxy composite were determined for different surface treatments of copper such as atmospheric pressure plasma treatment and nitric acid/ferric chloride treatment. The EM transmission characteristics of the FSS were also measured by the free space measurement system before and after surface treatments. Nitric acid/ferric chloride treatment of the FSS was found to be a promising method to enhance the bonding characteristics between the FSS and the E-glass/epoxy composite without change in the EM transmission characteristics of FSS.

Scattering characteristics of FSS comprised of L-shaped and one-turn helix shaped conductors for TE and TM excitation

The boundary value problem of doubly infinite periodic conductor arrays of L-shape and one-turn helix shape frequency selective surfaces (FSSs) backed by dielectric substrate are investigated by using modal expansion method. The moment method is employed by expressing the current induced on the metallic surfaces in terms of Piecewise Sinusoidal (PWS) functions. The variation of the reflection and transmission coefficients versus frequency for dielectric backed FSS is investigated for both transverse electric and transverse magnetic wave excitations at normal incidence. Reflection coefficients of dielectric backed FSS at normal and oblique incidence are plotted against frequency. The correctness of the algorithm is ensured by comparing the numerical results with the experimental results in the literature for an FSS composed of strips and proved to be as good.

Analysis of Frequency Selective Surfaces on Electrically and Magnetically Anisotropic Substrates

A full-wave analysis of frequency selective surfaces (FSS) supported by both electrically and magnetically anisotropic substrate is presented. The analytical procedure is based on Galerkin's method applied in the spectral domain, and the spectral Green's function for the considered structure is formulated based on Maxwell's equations directly. A series of FSS with different medium parameters, due to the rotation of the principal axes in the transverse plane, are computed efficiently, the effects of the rotation of principal axes on the resonance of the FSS are examined as functions of the rotation angle. Numerical results exhibit the influence of the electrical and magnetic anisotropy on the electromagnetic characteristics of FSS.

Scattering characteristics of FSS on two anisotropic layers for incident co‐polarized plane waves

AbstractA full‐wave analysis is presented for the scattering problem from a frequency‐selective surface (FSS) comprised of a periodic array of conducting patch elements on two dielectric layers. The formulation is carried out in the spectral domain, where the convolution form of the integral equation for the induced current is reduced to an algebraic one. This equation is then solved with the use of the immittance approach and the moment method in the spectral domain. A set of entire‐domain basis functions is included in the expansion for the unknown induced current. This analysis is computationally efficient. Numerical and experimental results are presented. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 33: 57–61, 2002; DOI 10.1002/mop.10231

Fundamental Constraints on the Electrical Characteristics of Frequency Selective Surfaces

This paper presents analytical constraints for the values which the reflection coefficient of any Frequency Selective Surface (FSS) can assume. This includes both patch and slot type FSS. The main assumption in this paper is that the FSS is a planar periodic surface constructed of infinitesimally thin conductors with a finite number of dielectric substrates and superstrates. In addition, only one periodic screen can be present, and it must be infinite in extent. Other than infinitesimal thickness, no assumptions are made on the shape of the periodic scatterer. The analysis presented in this paper includes the effects of dielectric layers, angle of incidence, and polarization. The results of the analytical constraints is the development of charts which can help one better understand fundamental FSS behavior. This includes a fundamental limit on how much power a lossy FSS can dissipate. This fundamental limit also applies to the amount of power that can be redistributed to grating lobes.