Frequency Selective Surface Unit Cell Research Articles

Beam‐switching millimetre‐wave antenna using cantilever‐based FSSs

A beam-switching antenna for millimetre-wave applications at 30 GHz is presented in this study. The radiation reconfigurability for a cylindrical dielectric resonator antenna (DRA) is obtained by using a cantilever-enabled frequency selective surface (FSS). The proposed cantilever-enabled FSS provides reconfigurable bandpass and band-stop performance with good isolation between them. The investigation of designed FSS is performed using electromagnetic simulation and an array of the proposed FSS unit cell is fabricated and measured using the free-space measurement method, which shows a good agreement with the simulation results. Finally, six panels of the 1 × 5 array of the proposed reconfigurable FSS are arranged in a hexagonal configuration around a cylindrical DRA to obtain a reconfigurable radiation pattern in the azimuth plane. A prototype of the proposed radiation reconfigurable DRA is fabricated and the switching radiation patterns are measured at 30 GHz.

A sub-wavelength polarization sensitive band-stop FSS with wide angular response for X- and Ku-bands

A sub-wavelength second-order band-stop frequency selective surface (FSS) is presented. The single layer FSS has a band reject operating mode for TE- and TM-polarizations incidence. Miniaturization of the FSS unit cell is achieved by coupling two resonators separated by single FR4 substrate. The unit cell size of the proposed FSS is 0.25λ0 × 0.25λ0, which λ0 is the free space wavelength at the center frequency (10 GHz). As experimental results proved, the proposed FSS has a great angle independence up to 60°. An equivalent circuit model is illuminated the operating principle of designed FSS. The validity of FSS is obtained by comparing experimental results and full-wave simulations.

Polarization independent dual-bandpass frequency selective surface for Wi-Max applications

In this article, the performance of polarization independent dual-bandpass frequency selective surface (FSS) is investigated. The proposed design of FSS unit cell comprises of metallic structure is based on customized plus shape within plus ring inside a square ring and etched on one side of FR4 substrate. The geometrical dimensions of unit cell are optimized in such a way that the structure possesses the dual-bandpass characteristic for Wi-Max applications. The aspect dimensions of unit cell are 0.16 λ × 0.16 λ × 0.013 λ with respect to first resonant frequency. The FSS provide stable response for different angle of incidence in transverse electric and transverse magnetic polarization. An equivalent circuit model of FSS is established and its results are verified by Advanced Design System tool. A prototype of FSS is designed, fabricated and measured. Good agreement between simulated and measured results verifies the dual-bandpass FSS.

Dual‐layer partially reflective surface antennas based on extended size unit cells for 60 GHz band WLAN/WPAN

In this study, planar dual-layer partially reflective surface, also known as frequency selective surface (FSS), antennas have been presented for 60 GHz band (57.24–65.88 GHz) wireless local area network (WLAN) and wireless personal area network (WPAN) applications. The FSS is excited through a microstrip patch antenna array of two elements designed at 63.72 GHz with return loss (S11) bandwidth and gain of 5.55 GHz and 13.2 dBi, respectively. Both the FSS unit cell and the feeding patch elements are set to be the same and they are designed based on the patch antenna size improvement method to convince the fabrication limitations imposed by the conventional printed circuit board etching process. Then three double layers FSS antennas have been designed with 2-elements, 12-elements and 24-elements in each FSS layer and measured gains of 15.6, 19.1 and 19.75 dBi, respectively, are achieved. It has also been found that when more layers and number of FSS elements are employed to improve the antenna gain, the overall S11 and gain bandwidth is reduced. In all the cases the measured results agreed well with the simulated results.

A Gain Enhancement and Flexible Control of Beam Numbers Antenna Based on Frequency Selective Surfaces

This paper describes a beam-switching antenna with high gain and flexible control of beam numbers based on frequency selective surfaces (FSSs). The proposed antenna is composed of an omnidirectional monopole antenna, a hexagon FSS screen, and six metallic sheets that surround the monopole antenna. The hexagon FSS screen contains six columns, each is made up of two FSS unit-cells. The beam-switching antenna is divided into six equal portions by six metallic sheets, which are employed here to improve the gain of the antenna. The proposed FSS unit-cell consists of the two metallic crosses connected by a pin-diode. The transmission characteristics of the FSS unit-cell are investigated for different pin-diode states. Therefore, by changing the states of the pin-diodes in the hexagon FSS screen, the proposed antenna can sweep six directions with gain enhancement in the azimuth plane. Moreover, it can also flexibly operate at multiple beams modes, including two-beam mode and three-beam mode with low power. This proposed antenna is fabricated and measured, showing good performances at 5.2 GHz. The maximum enhancement of the antenna gain is up to 7 dB, which is achieved by using the metallic sheets and verified with simulated and measured results, which show good agreement.

Equivalent Circuit Model for the Design of Frequency-Selective, Terahertz-Band, Graphene-Based Metamaterial Absorbers

Microwave absorbers have a wide range of potential applications at L, S, C, X, and Ku bands. But the development of a broadband absorber at terahertz frequencies has been a challenge. Here, an equivalent-circuit model is used to design and analyze a graphene-based frequency-selective surface (FSS) terahertz metamaterial absorber in the range of 0.1 to 4.0 THz. The effects of the chemical potential of the graphene layer, dielectric layer thickness, and FSS unit cell dimensions (i.e., periodicity, strip width, gap, etc.) on the absorption capability were determined for the proposed structure. An optimum absorber with negative permeability has a peak reflection coefficient of –37.9 dB at 1.2 THz, with a graphene chemical potential of 0.35 eV. A −10 dB absorption bandwidth of 0.68 THz (0.79 to 1.47 THz) is predicted. The metasurface behavior of the device is demonstrated in terms of frequency-dependent impedance, effective permittivity, and permeability. The results demonstrate the effectiveness of the structure for practical applications in the terahertz regime.

2.4/5.8 GHz WLAN Filtering in Secure Electromagnetic Applications: A Single Layer Frequency Selective Surface

This paper aims to propose a novel frequency selective surface (FSS) sketch for 2.45 and 5 GHz WLAN protection applications. The proposed FSS unit cell is printed on 10 × 10 mm2 FR4 substrate with thickness of 1.6 mm. Simple conductive elements are printed on top and bottom sides of the single substrate layer. Wise inclusion of elements and precise tuning of their dimensions yields in rejection of two frequency bands in 2.45 and 5 GHz WLAN frequency bands. The presented structure exhibit stable response against different angles of TE and TM polarized waves. Suitable performance of the designed FSS makes it a suitable choice for use in secure electromagnetic buildings, and communication filtering applications.

An FSS Structure Based on Parallel <italic>LC</italic> Resonators for Multiband Applications

An frequency selective surface (FSS) structure based on parallel LC resonators is proposed to achieve multiband bandpass filtering responses. The parallel LC resonator, implemented by a via-connected metallic line and a parallel-plate capacitor (PPC), serves as the basic element for intentionally constructing FSS unit cell, which exhibits a single-band bandpass filtering response. As a result, the proposed FSS structure can provide a multiband performance by introducing multiple VCMLs and PPCs with different resonance frequencies. Because of the compact resonator resulting from a PPC, the proposed FSSs feature miniaturized unit cell size inherently, for example, the single-band FSS element is as compact as 4.8% of the operating wavelength. Moreover, this kind of FSS structure is also beneficial for independent control of the frequency performance under different polarizations, efficient optimal design of desired resonance frequencies, and easy realization of multiband response with wideband ratio range (e.g., 1.13 to 3.32 for the dual-band FSS). Equivalent circuits of these FSSs are established for explaining the resonating mechanisms and precisely modeling the frequency performances. Finally, prototypes of the dual- and tri-band FSSs are fabricated and measured. The measured results exhibit stable filtering performance under different polarizations and incidence angles (up to 60°).

Tunable antenna radome based on graphene frequency selective surface

In this paper, a graphene-based frequency selective surface (FSS) is proposed. The proposed FSS exhibits a tunable bandpass filtering characteristic due to the alterable conductivity of the graphene strips which is controlled by chemical potential. Based on the reconfigurable bandpass property of the proposed FSS, a cylindrical antenna radome is designed using the FSS unit cells. A conventional omnidirectional dipole can realize a two-beam directional pattern when it is placed into the proposed antenna radome. Forward and backward endfire radiations of the dipole loaded with the radome is realized by properly adjusting the chemical potential. The proposed antenna radome is extremely promising for beam-scanning in terahertz and mid-infrared plasmonic devices and systems when the gain of a conventional antenna needs to be enhanced.

A novel FSS for gain enhancement of printed antennas in UWB frequency spectrum

AbstractThis paper presents a novel compact unilayer frequency selective surface (FSS) for ultra‐wideband (UWB) applications particularly for gain enhancement of printed antennas. The proposed FSS unit cell consists of simple metallic patterns printed on both sides of 14 mm × 14 mm FR4 substrate. The proposed FSS has very low transmission co‐efficient and linearly decreasing reflection phase over the bandwidth of 9 GHz in 3–12 GHz range, which makes it suitable candidate to provide in‐phase reflection for UWB antennas. For the validation of gain‐enhancement capability, the FSS is paired with a general monopole UWB antenna demonstrating an average gain improvement of 4 dB. The antenna composite has a maximum gain of 8.9 dBi.

Miniaturised bandstop frequency selective surface based on quasi‐lumped inductor and capacitor

A novel frequency selective surface (FSS) based on quasi-lumped inductor and capacitor is proposed to miniaturise FSS unit cell size. The quasi-lumped inductor and capacitor, implemented by meander line and parallel-plate capacitor, respectively, are connected in series to achieve a bandstop filtering response. This FSS provides the advantages of small unit cell size, independent control of the filtering response for different polarisations, and easy optimal design of desired resonant frequency and bandwidth. To validate the proposed design concept, a bandstop FSS operating at 2.42 GHz was designed, fabricated, and measured. Its unit cell size is only (λ 0/28) × (λ 0/28), where λ 0 refers to the resonant wavelength in free space. Both the simulated and measured results exhibit stable filtering performance under different polarisations and incident angles (up to 60°).

Tunable square slot FSS EC modelling and optimisation

An equivalent circuit model for tunable square slot frequency selective surfaces (FSS) is proposed. Tuning is achieved with the inclusion of a discrete capacitance element, at key points within the FSS unit cell. The equivalent circuit model takes into account the FSS physical attributes. The performance of the proposed equivalent circuit model was evaluated against results obtained from appropriate electromagnetic simulations. Results demonstrate the validity of the proposed equivalent circuit model, in which good estimations of the frequency response of FSS structures were obtained. A RMSE value of 190 MHz was extracted from the complete parametric simulation set. The model was further validated against measurements performed on a tunable active FSS prototype inside an anechoic chamber. Tuning of the FSS was achieved by means of bias voltage to modify the varicaps capacitance value. A relatively good agreement was verified between equivalent circuit model, electromagnetic simulations and measurements. Finally, this work is sought to be a useful contribution to the literature on this topic, by improving on the elementary models of such FSS structures and be useful as a good and fast first approach to determine approximate FSS unit cell dimensions.

A Bandpass Frequency Selective Surface With a Low Cross-Polarization Based on Cavities With a Hybrid Boundary

A novel low cross-polarization bandpass frequency selective surface (FSS) with low passband ripples and a steep roll-off at both sides of the passband is proposed. Different from available substrate integrated waveguide FSSs in which the boundary of every unit cell is electrically conducting, the proposed FSS unit cell is composed of two specially designed cavities with mixed electrically and magnetically conducting boundaries. These boundaries are formed by an array of shorting vias and complementary slots etched on both the top and bottom metallic patches, respectively. A bandwidth enhancement is achieved by properly merging three individual resonances excited in the two hybrid cavities and the slots within the required frequency range. An FSS centered at 4.58 GHz is fabricated and its near- and far-field performances are measured, with the results in good agreement with the prediction. The characteristics, including a steep roll-off, low passband ripples, a low cross-polarization, and stability at oblique incidence angles, are verified by the measurement.

Reconfigurable frequency selective surface for beam‐switching applications

A novel design for a beam-switching antenna based on a new reconfigurable frequency selective surface (FSS) is presented at 2.1 GHz operating frequency. The antenna system consists of an omnidirectional antenna and a cylindrical FSS for controlling its radiation pattern characteristics. The discontinuous split-ring resonator (SRR) cross-shape FSS is composed of 12 FSS unit cells with 4 active elements in each one. To reconfigure the radiation pattern of the antenna, a PIN-diode is specifically placed in the discontinuity of the FSS hybrid element for its switching functions. The antenna radiation sector is determined by the off-state diodes. This design is used to realise a beam-switching active antenna covering all azimuth angles. The measurement results are in line with the simulation and confirm the proposed configuration of the antenna. The measurement of the proposed design at the operating frequency resulted in a gain of 8.1 dBi. This antenna can be used in the base station of the wireless communication systems.

High Gain Compact Microstrip Patch Antenna for X-Band Applications

This paper present a design of a Frequency Selective Surface (FSS) to improve gain and efficiency of a micro-strip patch antenna operating in X-band at 10 GHz. The band-stop frequency selective surface (FSS) designed at the operating frequency of the antenna is used. FSS structure is configured as a super-strate for the micro-strip patch antenna. The main goal of this paper is design a compact micro-strip antenna module (micro-strip patch and FSS structure). Simulation results using CST studio showed that high gain (54 % increment) and efficiency is increased to 97% have been achieved by the proposed antenna module (MS and FSS). The equivalent circuit of proposed FSS unit cell in ADS software has been evaluated and compared to simulation results (CST studio) to improve characteristics of the antenna. The proposed antenna module is extremely compact high gain and it can be used for X-band applications.

Circularly polarized inverted stacked high gain antenna with frequency selective surface

ABSTRACTIn this work; the novel design of dumbbell shaped frequency selective surface (FSS) is demonstrated as superstrate. The array of this designed FSS structure is incorporated on two different antennas; (1) Microstrip Patch Antenna (MPA), and (2) Inverted Stacked Microstrip Patch Antenna (ISMPA). The FSS unit cell reflection magnitude is nearly 0.95 in the vicinity of both antennas resonance frequencies. Based on the ray tracing phenomenon multiple reflections occur between superstate and ground plane. So by this phenomenon the gain of circular patch and the ISMPA is enhanced by 6.02 dBic and 5.1 dBic respectively. In the measured results, the impedance bandwidth of MPA and ISMPA are 6.66% (5.8–6.2 GHz) at 6 GHz center frequency and 5.3% (5.53–5.83 GHz) at 5.67 GHz center frequency respectively. The corner truncated dumbbell shaped FSS layer also acts as a polarizer. The axial ratio 3 dB band width of MPA and ISMPA are 8.66% (5.64–6.16 GHz) and 12.6% (5.52–6.24 GHz). Here simulation results are shown good agreement with measured results. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:732–740, 2016

Modeling and Analysis of Miniaturized Frequency-Selective Surface Based on 2.5-Dimensional Closed Loop With Additional Transmission Pole

The 2.5-dimensional closed loop is investigated to constitute a novel miniaturized frequency-selective surface (FSS) whose electric size of one unit cell is as small as $0.048\,{\lambda_0} \times 0.048\,{\lambda_0}$ . For miniaturization, two pairs of orthogonal split square rings are connected in series by four vias array in the FSS unit cell. Thus, this FSS exhibits polarized insensitivity for different incident angles. An equivalent circuit model is implemented to give a physical insight of the working mechanism of the proposed miniaturized FSS. Moreover, the transmission zero and transmission pole are discussed by the full-wave simulations and equivalent circuit model. The additional transmission pole can be used to improve the sharp frequency-selective performance of the proposed miniaturized FSS. The results show a good consistency between the simulation, modeling, and measurement.

High Gain Compact Microstrip Patch Antenna for X-Band Applications

This paper present a design of a Frequency Selective Surface (FSS) to improve gain and efficiency of a micro-strip patch antenna operating in X-band at 10 GHz. The band-stop frequency selective surface (FSS) designed at the operating frequency of the antenna is used. FSS structure is configured as a super-strate for the micro-strip patch antenna. The main goal of this paper is design a compact micro-strip antenna module (micro-strip patch and FSS structure). Simulation results using CST studio showed that high gain (54 % increment) and efficiency is increased to 97% have been achieved by the proposed antenna module (MS and FSS). The equivalent circuit of proposed FSS unit cell in ADS software has been evaluated and compared to simulation results (CST studio) to improve characteristics of the antenna. The proposed antenna module is extremely compact high gain and it can be used for X-band applications.

Angularly Stable Frequency Selective Surface With Miniaturized Unit Cell

A new type of Frequency Selective Surface (FSS) with miniaturized resonator element is proposed. The FSS structure is shown to have a FSS unit cell dimension that is miniaturized to 0.067 $\lambda_{{{0}}}$ . Miniaturization of the FSS unit cell is achieved by coupling two meandered wire resonators separated by single thin substrate layer. The capacitance due to the small separation between the meandered wire elements results in a lowering of the resonant frequency. To demonstrate the validity of the design, the meandered wire resonator FSS was fabricated and tested using a free space measurement facility. The FSS produces a stable angular response up to 80 degrees for TE and TM incident angles.

X-Band Tunable Frequency Selective Surface Using MEMS Capacitive Loads

A tunable frequency selective surface (FSS) based on slotted ground is presented. Tuning of the resonance frequency is achieved by using a metallic MEMS bridge over the slot. The bridge acts as a capacitive load, increasing the equivalent capacitance, and so decreasing the resonance frequency. Electromagnetic and electromechanical simulations are performed to investigate the designed FSS. S-parameter measurements of the FSS unit cell are performed in a waveguide simulator, showing more than 1.7 GHz frequency shift in the X-band, achieved by using only one MEMS bridge. A measured bandwidth of 400 MHz at the resonance frequency of 9.59 GHz is achieved. The designed MEMS bridge benefits from an unconventional method of using SU-8 as the sacrificial layer, resulting in low loss at high frequencies (3.2 dB loss at the resonance frequency of 9.59 GHz). Devices with different heights of the MEMS bridge were fabricated to study the variation in the resonance frequency. The MEMS bridge was tested at fixed heights. Simulated and measured results show excellent agreement. An FSS array is designed based on the FSS unit cell results. The design procedure to maximize the quality factor and controllable frequency range, and improve the radiation characteristics of the FSS array is discussed. Further simulations are performed to examine the performance of the FSS array with regards to grating lobes, oblique incidence and tunability.