Miniaturized Unit Cell Research Articles

Miniaturized Low-Profile Circularly Polarized Metasurface Antenna Using Capacitive Loading

A miniaturized circularly polarized (CP) metasurface (MS) antenna using capacitive loading is investigated. First, one novel miniaturized MS unit cell is proposed. By introducing a pair of capacitive-loading strips inserted along the diagonal of a corner-truncated patch, 56% size reduction is achieved for this miniaturized unit cell. Accordingly, a compact CP MS antenna of a $4\,\,\times \,\,4$ array composed by the miniaturized unit cells is designed and fed by a slot structure. Compared with the conventional CP MS antenna without capacitive-loading strips, 63% overall size reduction can be achieved. Furthermore, the CP radiation mechanism of the CP MS antenna is revealed and explained clearly using the characteristic mode analysis (CMA). For demonstration, a prototype of the proposed CP antenna was fabricated and measured. The measured 3 dB axial ratio (AR) band is from 3.33 to 3.63 GHz, and the 10 dB impedance band is from 3.02 to 3.82 GHz, while 6.5 dBi gain is realized within the CP operating band.

Modified Minkowski Fractal Unit Cell for Reflectarrays with Low Sensitivity to Mutual Coupling Effects

A single-layer miniaturized reflectarray element with low sensitivity to mutual coupling effects of surrounding elements is presented in this paper. The configuration is proposed to preserve the effectiveness of the infinite array approach in those applications requiring reflectarrays with very small interelement spacing. The inherent ability of the proposed geometry to be adopted in highly miniaturized cells is demonstrated through an extensive analysis of mutual coupling effects on reflectarray phase design curves. In order to prove the independence of the proposed cell to mutual coupling effect, the phase curve variations due to the presence of different surrounding elements with respect to the case of identical cells are evaluated using the well-known extended local periodicity method. Small and negligible mutual coupling errors are retrieved for the proposed miniaturized unit cell, thus demonstrating lower sensitivity to mutual coupling adverse effects.

Design and equivalent circuit model extraction of a third-order band-pass frequency selective surface filter for terahertz applications

In this paper, a third-order band-pass frequency selective surface (FSS) filter is proposed for terahertz applications. The presented FSS filter is designed based on miniaturized unit cells and a fractional bandwidth of 72% around 0.775 THz is achieved. In addition, a high transmission magnitude is obtained with an acceptable flatness in comparison to previous reports. In order to verify the numerical results, an equivalent circuit model of the proposed spatial filter is introduced considering both normal and oblique incident angles. The sensitivity of the filter with respect to the incident wave angle is investigated in the range of 0–60° whereas the obtained performance is acceptable for various incident angles in the mentioned range. Moreover, the effects of altering different geometrical parameters are studied and justified based on the extracted equivalent circuit model.

Dual stop band frequency selective surface for C and WLAN band applications

A miniaturized unit cell design of Frequency Selective Surface (FSS) to produce stop band characteristics for two bands is presented. The presented unit cell structure is showing the band filtering characteristics for dual frequency band specifically C-band for satellite communication and Wireless Local Area Network (WLAN). The designed FSS structure is comprised of I shaped and modified I shaped metallic strips. The distinct unit cells of suggested are investigated for band filtering characteristics and finally integrated on a single unit cell for dual-band filtering applications. The I shaped and modified I shaped unit cell is producing band filtering properties at center frequencies like 4 GHz and 5.5 GHz respectively. The presented FSS design is modeled on an FR-4 substrate with dielectric constant of 4.4 and the dimension of the unit cell is 10 × 10 × 1.6 mm3. The fabricated FSS structure is simulated and measured for its characteristics verification like S11 and S21 and it has been found a satisfactory agreement in simulated and measured results.

Optimal Design of Miniaturized Reflecting Metasurfaces for Ultra-Wideband and Angularly Stable Polarization Conversion

An ultra-wideband linear polarization converter based on a reflecting metasurface is presented. The polarizer is composed by a periodic arrangement of miniaturized metallic elements printed on a grounded dielectric substrate. In order to achieve broadband polarization converting properties, the metasurface is optimized by employing a genetic algorithm (GA) which imposes the minimization of the amplitude of the co-polar reflection coefficient over a wide frequency band. The enhanced angular stability of the polarization converter is due to the miniaturized unit cell which is obtained by imposing the maximum periodicity of the metasurface in the GA optimization process. The pixelated polarization converter obtained by the GA exhibits a relative bandwidth of 102% working from 8.12 GHz to 25.16 GHz. The analysis of the surface current distribution of the metasurface led to a methodology for refining the optimized GA solution based on the sequential removal of pixels of the unit cell on which surface currents are not excited. The relative bandwidth of the refined polarizer is extended up to 117.8% with a unit cell periodicity of 0.46 mm, corresponding to λ/20 at the maximum operating frequency. The performance of the proposed ultra-wideband polarization metasurface has been confirmed through full-wave simulations and measurements.

건물 내 주파수 선택적 공간 구현을 위한 인쇄전자 기술 기반 필름형 주파수 선택 표면구조 설계

In this paper, a frequency selective surface(FSS) with bandstop operation for radio-frequency spectrum management is presented. The proposed FSS is composed of patterns of fractal-based miniaturized unit cells for stable performance for angles of incidence and polarizations. For practical applications requiring high productivity and environmental compatibility, we fabricated a film-type FSS by screen-printing using Ag ink, rather than a conventional manufacturing method using a printed circuit board. To validate this study, we measured the transmission characteristics of the proposed FSS using the free-space measurement method, and observed the received strength of signal penetrating the FSS film applied to a wall.

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°).

An Angularly Stable Dual-Band FSS With Closely Spaced Resonances Using Miniaturized Unit Cell

A novel miniaturized-element dual-band frequency selective surface (FSS) with closely spaced resonance is presented in this letter. The proposed FSS comprises of meander lines printed on a single-layer dielectric substrate to provide dual stopband characteristic. Compared to previously published spatial filters, the proposed FSS has better miniaturization characteristic having the unit-cell size of $0.065\lambda _{0} \times 0.065\lambda _{0}$ , where $\lambda _{0}$ corresponds to free space wavelength of the lower resonance frequency. In addition, the operating bands are closely located exhibiting the frequency ratio as low as 1.29. The surface current distribution and the equivalent circuit model are illustrated to explain the resonance behavior of the designed FSS. Furthermore, the proposed structure is polarization-independent and angularly stable for both TE and TM polarizations. A prototype of the dual-band FSS is fabricated and measured, which validates the simulated responses under normal and oblique incidence.

An Ultrathin Bandpass Frequency Selective Surface With Miniaturized Element

An ultrathin bandpass frequency selective surface (FSS) with miniaturized unit cell is proposed in this letter. A significant coupling capacitance can be introduced by the large overlapping areas between the two metallic layers of the structure; therefore, the dimension of the unit cell can be decreased to only 0.050λ × 0.050λ, where λ represents the free-space wavelength corresponding to the resonant frequency. The dimension of the proposed FSS can be further miniaturized to 0.034λ × 0.034λ as three more ultrathin patch array layers are added symmetrically. In addition, the proposed FSS exhibits excellent stability for different incident angles and different polarizations. A prototype of the proposed FSS is fabricated and measured, and the measured results agree well with the simulated results.

An FSS Structure With Geometrically Separable Meander-Line Inductors and Parallel-Plate Capacitors

A frequency selective surface (FSS) structure with geometrically separable meander-line inductors (MLIs) and parallel-plate capacitors (PPCs) is proposed. For this FSS structure, the filtering responses for different polarizations and resonance frequencies are realized through separate subcells. For example, to achieve a single-band bandpass performance, two subcells, acting as parallel LC resonators for transverse-electric and transverse-magnetic polarizations, respectively, are implemented by MLIs and PPCs. Because the MLIs and PPCs provide increased equivalent inductance and capacitance, respectively, this FSS provides a miniaturized unit cell size of $\lambda _{0}/20 (\lambda _{0}$ refers to the resonance wavelength), and its −3 dB bandwidth can be designed by independently adjusting the equivalent inductance and capacitance. A design example shows the easy control of −3 dB bandwidth ranging from 13.6% to 49% with respect to the center frequency. Furthermore, because of the separable subcells, the FSS performances for different polarizations are independently controllable, and it can be readily extended to achieve dual-band bandpass performance with a band ratio ranging from 1.35 to 3.8. In addition, to model the FSS frequency performance precisely, equivalent circuits and closed forms are developed, which serve as a substitute for commercial software for efficient FSS design. Finally, some prototypes are fabricated and measured. All the measured results show that the proposed FSS designs exhibit stable performance under different polarizations and incidence angles (up to 60°), and they exhibit good consistency with those from the full-wave simulations.

Angular- and Polarization-Insensitive Metamaterial Absorber Using Subwavelength Unit Cell in Multilayer Technology

In this letter, we propose a novel metamaterial absorber with angular and polarization insensitivity using multilayer technology. The miniaturized unit cell of the proposed absorber consists of a split-ring-cross resonator (SRCR) on the middle layer with a metallic ring on the top layer and meander line on the bottom layer. Because additional capacitance and inductance are generated by metallic patterns on the top and bottom layers, the resonance frequency is shifted to a lower frequency and the electrical size of the unit cell dramatically decreases. The principle of miniaturizing the unit cell is described in detail by a parametric study, and the performance of the proposed absorber is demonstrated by full-wave simulation and measurement. The proposed absorber can achieve a high absorptivity at 10.28 GHz and maintain it for different polarizations and incidence angles.

X-band Band-pass Frequency Selective Surface for Radome Applications

A low profile multi layer miniaturized unit cell frequency selective surface (FSS) with second-order band-pass response is design. The metallic layers in the form of capacitive patches and inductive grids are separated by dielectric substrates. The non-resonant sub-wavelength unit cells with unit cell dimensions and periodicities on the order of 0.15λ. The overall thickness of approximately 0.03λ is designed which is useful at lower frequencies with long wavelengths. The FSS exhibit a stable frequency response to different angles of incidence and polarizations. The analysis and synthesis of the FSS is done using equivalent circuit method and simulated using CST microwave studio at X-band.

X-band Band-pass Frequency Selective Surface for Radome Applications

A low profile multi layer miniaturized unit cell frequency selective surface (FSS) with second-order band-pass response is design. The metallic layers in the form of capacitive patches and inductive grids are separated by dielectric substrates. The non-resonant sub-wavelength unit cells with unit cell dimensions and periodicities on the order of 0.15λ. The overall thickness of approximately 0.03λ is designed which is useful at lower frequencies with long wavelengths. The FSS exhibit a stable frequency response to different angles of incidence and polarizations. The analysis and synthesis of the FSS is done using equivalent circuit method and simulated using CST microwave studio at X-band.

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.

Silver Nanoparticle-Based Inkjet-Printed Metamaterial Absorber on Flexible Paper

In this letter, a novel, flexible inkjet-printed metamaterial absorber is proposed. The unit cell consists of a miniaturized Jerusalem-cross resonator and a completely conductive bottom. Because the conductive patterns are inkjet-printed using silver nanoparticle inks on paper, the proposed metamaterial absorber is flexible. It is also eco-friendly because it does not produce any chemical waste. In this letter, the working principle of the proposed miniaturized unit cell is explained, and parametric simulations are described. The inkjet-printing process is delineated, and the silver nanoparticle inks and paper used are characterized. The performance of the proposed absorber is demonstrated with a full-wave simulation and measurements at the X-band. The experimental results show that the absorption rate at 9.09 GHz is greater than 99% at the normal incidence. Angular and polarization insensitivity are also experimentally demonstrated.

A Circuit Model for the Design of Self-Excited EBG Resonator Antennas With Miniaturized Unit Cells

A circuit model based on Bloch theory is introduced to simplify analysis and design of antennas composed of thick metal electromagnetic band-gap (EBG) cells with large intercell coupling capacitance. The cells are composed of thick metal patches periodically deployed on a metal-backed dielectric slab. Two versions of cells are presented that provide large intercell capacitance, one with narrow high aspect ratio (HAR) gaps between cells and the other with interdigitated gaps between cells. This large capacitance reduces the antenna resonance and dramatically miniaturizes the EBG cells. Three cascaded unit cells are used to demonstrate the applicability of the circuit model to characterize the recently introduced self-excited EBG resonator antenna. Full-wave numerical analysis and experimentation validate the robustness and accuracy of the model over large variations in electrical/physical cell dimensions.

A Low-Profile Third-Order Bandpass Frequency Selective Surface

We demonstrate a new class of low-profile frequency selective surfaces (FSS) with an overall thickness of lambda/24 and a third-order bandpass frequency response. The proposed FSS is a three layer structure composed of three metal layers, separated by two electrically thin dielectric substrates. Each layer is a two-dimensional periodic structure with sub-wavelength unit cell dimensions and periodicity. The unit cell of the proposed FSS is composed of a combination of resonant and non-resonant elements. It is shown that this arrangement acts as a spatial bandpass filter with a third-order bandpass response. However, unlike traditional third-order bandpass FSSs, which are usually obtained by cascading three identical first-order bandpass FSSs a quarter wavelength apart from one another and have thicknesses in the order of lambda/2 , the proposed structure has an extremely low profile and an overall thickness of about lambda/24 , making it an attractive choice for conformal FSS applications. As a result of the miniaturized unit cells and the extremely small overall thickness of the structure, the proposed FSS has a reduced sensitivity to the angle of incidence of the EM wave compared to traditional third-order frequency selective surfaces. The principles of operation along with guidelines for the design of the proposed FSS are presented in this paper. A prototype of the proposed third-order bandpass FSS is also fabricated and tested using a free space measurement system at C band.

Design and negative refraction investigation of a compact left‐handed metamaterial

AbstractA compact left‐handed metamaterial (LHM) with miniaturized unit cell and broad bandwidth is proposed. By optimization of design, the relative bandwidth is up by 21.1%, and the unit cell electrical length is only 0.072 at the central frequency where the LHM is available. The negative refraction characteristics of the wedge‐shaped LHM are investigated using full‐wave simulation, and it is shown that the designed LHM exhibits negative refraction in a broad band range of 8.5–10.5 GHz, and hence the existence of the LHM is proven. Copyright © 2008 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Design and double negative property verification of C band left‐handed metamaterial

AbstractIn this article, a left‐handed (LH) metamaterial with miniaturized unit cell and broad bandwidth is designed. Its relative bandwidth is 56.4%, and the unit cell electrical size is 0.067 at the central frequency where the LH metamaterial is available. The effective permittivity and effective permeability are extracted from the transmission and reflection data at normal incidence for the LH metamaterial proposed here. The double negative (DNG) property is shown by the simultaneously negative effective permittivity and effective permeability and is confirmed by the equivalent circuit. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 1732–1736, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21763

Design and modeling for 1.7—2.7 GHz broad-band left-handed material with miniaturized unit cell and its characterization

An 1.7—2.7 GHz broad-band left-handed (LH) metamaterial with miniaturized unit cell is designed. The relative bandwidth of designed metamaterial is up to 45.5%， the electrical length of its unit cell is less than 0.035，and the transmission loss per unit cell is less than 0.75 dB in the whole operational band of the LH metamaterial. In this paper, the reflection and transmission characteristics of a semi-infinite LH metamaterial plate consisting of LH metamaterial cells is simulated, and the wave number, phase velocity, refraction index, effective permittivity and effective permeability are calculated. The results show the real part of the wave number and the refraction index and the velocity are negative while the real part of the effective permittivity and effective permeability are both negative in the 1.7—2.7 GHz band range.