Frequency Selective Surface Screens Research Articles

A simple dual‐band frequency selective surface

AbstractDesign and experimental investigations are presented for a dual‐band frequency selective surface (FSS) with perfectly conducting rectangular patch elements. The work was developed in two steps. In the first step, two single‐band FSS screens were designed to obtain resonant frequencies at 9.5 GHz and 10.5 GHz, each one with about 1.5 GHz bandwidth. In the second step, these single FSS screens were cascaded and separated by an air gap layer to achieve a dual‐band response. The proposed dual‐band FSS screen is easy to analyze and to fabricate with low cost materials and exhibits a low weight and easy to handle structure. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 942–944, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24236

Concrete ingots covered with interdigital FSS screens as broadband microwave absorbers

This study investigates the construction and measurement of broadband microwave absorbers constructed of ‐shaped/comb‐shaped interdigital frequency selective surface (FSS) screens and concrete ingots to enhance frequency response. By applying the comparison decrement method, reflectivity (R) is determined from the return loss of the absorber and the conducting surface, such that R can recognize the characteristics of microwave absorbers. Experimental results indicate that 69.8% of the bandwidth's frequency responses are below ‐10dB when using copper concrete ingots, and 66.1% are below ‐10dB when using fiber concrete ingots in perpendicular polarization (A-) to the π‐shaped FSS absorber. Using the same measurements, 71.6%, and 66.1% of the bandwidth percentage are below ‐10dB with copper and fiber concrete ingots, respectively, for comb‐shaped FSS absorbers in the C‐band applications.

Directivity Enhancement of Printed Antennas Using a Class of Metamaterial Superstrates

In this paper, we present some applications of metamaterial superstrates for directivity enhancement of printed antennas. Three different types of superstrates, viz., multilayer dielectric slabs, electromagnetic band gap (EBG) materials, and frequency selective surfaces (FSSs) are discussed. We first present the design of a multilayer dielectric slab, consisting of high and low permittivity dielectric layers and air-gap tuners for suppressing the grating lobes of patch array antennas. Next, a dielectric-rod EBG-type superstrate with two defect frequencies is proposed for dual-band directivity enhancement of a patch antenna at a boresight. With this design we can increase the degrees of freedom that adjust the level of directivity enhancement and operating frequency location, relative to those of the multilayer dielectric slab type. Finally, an FSS superstrate consisting of two-layered FSS screens for dual-band directivity enhancement is introduced as an alternative to an EBG type of dielectric superstrate to reduce its height and facilitate the fabrication process.

EM characteristics of the RAS composed of E-glass/epoxy composite and single dipole FSS element

From the methods to reduce radar cross section (RCS) such as shaping of the target, radar absorbing material (RAM), and radar absorbing structure (RAS), the RAS composed of frequency selective surface (FSS) screens and low-loss composite materials is used widely because the FSS screen transmits or reflects electromagnetic (EM) waves selectively and the composite material withstands external loads. In this study, the RAS composed of the E-glass/epoxy composite and single dipole FSS element was fabricated by printed circuit board (PCB) manufacturing process, and their EM transmission characteristics, such as a resonant frequency, a minimum transmission loss, and a transmission bandwidth, were measured in the X-band frequency range by the free space method with respect to the size of dipole element and its periodicity of array.

Small periodicity FSS screens with enhanced bandwidth performance

A novel approach for obtaining small periodicity frequency selective surface (FSS) screens with enhanced bandwidth performance is proposed. The issue of miniaturising FSS unit cells has gained extreme importance in recent metamaterials applications. To this end several procedures have been suggested in the literature. However, such procedures usually result in a bandwidth degradation as long as miniaturisation is improved. On the contrary, the bandwidth performance of the structures here presented is enhanced as the FSS periodicity gets smaller. Application of such structures to the synthesis of artificial magnetic conductors are also presented.

Analysis of multiple FSS screens of unequal periodicity using an efficient cascading technique

In this paper, we present an efficient cascading procedure for analyzing frequency selective surface (FSS) systems consisting of multiple FSS screens of unequal periodicity embedded in multiple dielectric layers. In this procedure, we first find a global period for the FSS system by studying the composite in its entirety. Next, we compute the scattering matrix [S] of each of the FSS subsystems for the global Floquet harmonics by applying a relationship we establish that maps the [S] matrix of the subsystem for the individual Floquet harmonics to that for the global harmonics. This mapping-cum-filling process substantially reduces the effort needed to compute the [S] matrix of a subsystem. Finally, we compute the [S] of the entire system by applying a modified cascading formulation, in which one matrix inversion step is eliminated, resulting in a reduction in the total computing resource requirement as well as time. Two numerical examples are given to illustrate the efficiency and effectiveness of the technique.

Application of the differential-evolution strategy to the design of frequency-selective surfaces

An optimization approach based on the diffential evolution strategy (DES) is applied to the design of frequency-selective surfaces (FSS). The spectral Galerkin method is used to analyze the electromagnetic scattering from a FSS screen while DES is used to tune the FSS unit-cell dimensions and dielectric properties in order to achieve the prescribed frequency responses. The DES is compared to the real-coded genetic algorithm. The simulated results of FSS dipole arrays are presented, which demonstrate that DES is a more simple, yet more efficient and more robust, method for the design of FSS. © 2005 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2005.

The design synthesis of multiband artificial magnetic conductors using high impedance frequency selective surfaces

This paper introduces several different design methodologies for multiband artificial magnetic conducting (AMC) surfaces. The paper begins by investigating the multiband properties exhibited by a conventional electromagnetic bandgap (EBG) AMC that consists of a frequency selective surface (FSS) on top of a thin dielectric substrate with a PEC back plane. The higher-order resonances associated with these surfaces have not been discussed in detail to date, as previous research has been concerned only with exploiting the primary resonant frequency. However, it will be shown that by understanding and making appropriate use of these higher order resonances, it is possible to design multiband AMC surfaces that work for nearly any desired combination of operating frequencies. The first multiband AMC design approach that will be considered is based on the introduction of FSS screens that have fractal or nearly fractal unit cell geometries. This is followed by a more general and robust genetic algorithm (GA) technique for the synthesis of optimal multiband AMC surfaces. In this case, a GA is used to evolve multiband AMC surface designs by simultaneously optimizing the geometry and size of the FSS unit cell as well as the thickness and dielectric constant of the substrate material. Finally, several examples of multiband AMC surfaces are presented, including some practical dual-band and tri-band designs genetically evolved for operation at GPS and cellular frequencies, as well as an example illustrating the success in creating a multiband AMC surface with angular stability.

Design of double-square-loop frequency-selective surfaces using differential evolution strategy coupled with equivalent-circuit model

The design of frequency-selective surfaces (FSSs) with double-square-loop patch elements using the differential evolution strategy coupled with an equivalent circuit model (ECM) is proposed in this paper. A very efficient optimization algorithm, the differential evolution strategy is employed to tune the FSS unit-cell dimensions. In the fast computational method, the equivalent-circuit model is also employed to analyze the electromagnetic scattering from the FSS screen. The simulated results are in good agreement with the measured results. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 44: 159–162, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20575

Design of a frequency selective surface (FSS) with very low cross-polarization discrimination via the parallel micro-genetic algorithm (PMGA)

We discuss the design of a frequency selective surface (FSS) with low cross-polarization discrimination. In the past, FSS screens have been employed to improve the cross-polarization performance. The objective of this paper is to synthesize an FSS subreflector with low cross-polarization via the application of a parallel binary coded micro-genetic algorithm (PMGA). The PMGA optimizes the metallization pattern and the periodicity of the FSS screen in both the x- and y-directions to maintain a low cross-polarization level for a wide band of frequencies and a range of incident angles.

Technique for analysing cascaded frequency selective surface screens with dissimilar lattice geometries

The paper presents an efficient technique for analysing cascaded frequency selective surfaces (FSS) with non-commensurate periodicities by using an iterative approach based on the discrete plane wave spectrum (PWS) expansion. In this method, the tangential electric fields at the interfaces of the screens are first expanded in a set of transverse electric and transverse magnetic waves, and the responses of the individual FSS screens are derived for each of these waves. The transmission and reflection characteristics of the composite structure are then computed in an iterative manner, circumventing the need for matrix inversions. Such inversions can be extremely expensive in terms of CPU time and memory for non-commensurate FSS, because the analysis of the structures can no longer be reduced to that of a single cell by invoking Floquet's theorem. Representative numerical examples are presented to illustrate the computational advantage gained by using the proposed approach as apposed to a conventional scattering matrix cascading technique, which is strictly valid only for composites with commensurate periodicities.

An efficient technique for analyzing multiple frequency‐selective‐surface screens with dissimilar periods

AbstractThis Letter presents an efficient technique for analyzing multiple frequency‐selective surfaces (FSSs) with noncommensurate periodicities based on the discrete plane‐wave spectrum (DPWS) expansion method. In this method, the tangential electric fields at the interfaces of the screens are first expanded in a set of transverse electric and transverse magnetic waves, and the responses of the individual FSS screens are derived for each of these waves. The transmission and reflection characteristics of the composite structure are then computed in an iterative manner, circumventing the need for matrix inversions, which can be extremely expensive in terms of CPU time and memory for noncommensurate FSSs. Representative numerical examples are presented to illustrate the computational advantage gained by using the proposed approach as opposed to the conventional generalized scattering matrix technique. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 35: 23–27, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10506

Application of a microgenetic algorithm (MGA) to the design of broadband microwave absorbers using multiple frequency selective surface screens buried in dielectrics

Over the years, frequency selective surfaces (FSSs) have found frequent use as radomes and spatial filters in both commercial and military applications. In the literature, the problem of synthesizing broadband microwave absorbers using multilayered dielectrics through the application of genetic algorithms (GAs) have been dealt with successfully. Spatial filters employing multiple, freestanding, FSS screens have been successfully designed by utilizing a domain-decomposed GA. We present a procedure for synthesizing broadband microwave absorbers by using multiple FSS screens buried in a dielectric composite. A binary coded microgenetic algorithm (MGA) is applied to optimize various parameters, viz., the thickness and relative permittivity of each dielectric layer; the FSS screen designs and materials; their x- and y-periodicities; and their placement within the dielectric composite. The result is a multilayer composite that provides maximum absorption of both transverse electric (TE) and transverse magnetic (TM) waves simultaneously for a prescribed range of frequencies and incident angles. This technique automatically places an upper bound on the total thickness of the composite. While a single FSS screen is analyzed using the electric field integral equation (EFIE), multiple FSS screens are analyzed using the scattering matrix technique.

On the application of the microgenetic algorithm to the design of broad-band microwave absorbers comprising frequency-selective surfaces embedded in multilayered dielectric media

In this paper, we present a procedure for synthesizing broad-band microwave absorbers incorporating frequency-selective surface (FSS) screens embedded in dielectric media using a binary coded genetic algorithm (GA). The GA simultaneously and optimally chooses the material in each layer, thickness of each layer, FSS screen periodicity in the z- and y-directions, its placement within the dielectric composite, and the FSS screen material. Additionally, the GA generates the cell structure of the FSS screen. The result is a multilayer composite that provides maximum absorption of both TE and TM waves for a prescribed range of frequencies and incident angles. This technique automatically places an upper bound on the total thickness of the composite.

The use of domain decomposition genetic algorithms exploiting model reduction for the design of frequency selective surfaces

The application of domain decomposition genetic algorithms to the design of frequency selective surfaces (FSSs) is discussed. The analysis of FSS screens is briefly reviewed, along with a method of accelerating their characterization with a rational Krylov model order reduction technique. Using this technique, a hybrid genetic algorithm (which is a type of domain decomposition genetic algorithm that incorporates a local optimization scheme for real-coded quantities) is applied to the optimization of frequency selective surfaces. Several designs of frequency selective surfaces are presented, and the applicability of the algorithm to other types of problems is discussed.

Dichroic design for the orbiting VLBI earth station antenna

The design and performance of a single screen frequency selective surface (FSS) with gridded square loop patch element are described for diplexing the Xand Ku-band signals in an orbiting very long baseline interferometer (OVLBI) earth station reflector antenna system. The FSS grids were designed using an analysis code incorporating the accurate integral equation technique. The effects of the dielectric substrate and superstrate are accurately evaluated by this technique. Excellent agreement is obtained between the predicted and measured results. This validates the FSS design using the gridded square loop element. If the grid is sandwiched between two 0.889 mm thick Teflon slabs, the resonant frequency drift is noticeably reduced as the incident angle steered from normal to 40 degrees . >