Miniaturized Unit Cell Research Articles

Design of 2.5-D miniaturized frequency selective surface with enhanced oblique stability

This paper presents a miniaturized 2.5-D frequency selective surface (FSS) that exhibits a band stop response at frequency of 1.5 GHz. In the unit cell, the meander patterns on both side of the substrate are connected in series by four vias. Moreover, the meandered pattern in each quadrant is also connected with one of the meander patterns of the adjacent unit cell. In this manner, a 2.5-D closed loop is created with large perimeter. The enlarged perimeter amplifies the effective inductance and leads to a decrease in both the resonant frequency and the dimensions of unit cell. Subsequently, the proposed FSS demonstrates excellent miniaturization with an overall size of 0.038 λ 0 × 0.038 λ 0. Moreover, the frequency response is highly stable up to 86° for both TE and TM polarization. The resonance mechanism of the designed FSS is explicated through distribution of surface current and electric field. The testing board of the proposed FSS has been fabricated for the verification of the design. The measured frequency response of the prototype are congruent with the simulation results. The distinguished features of the constructed structure are enhanced angular stability, miniaturized unit cell, low profile, simple geometry and easy fabrication.

Design a Compact and Miniaturized Unit Cell in Substrate Integrated Plasmonic Waveguides

This paper presents a novel procedure to design a compact and miniaturized unit cell in the substrate integrated plasmonic waveguide (SIPW) structures. The slot of the unit cell is automatically obtained in this method without needing any prior knowledge of its shape. The method is based on topology optimization through pixelization of the slot surface in the unit cell and uses a combination of binary particle swarm optimization (BPSO) and commercial electromagnetic (EM) software. With this method, first, the shapes of the two unit cells are engineered to arbitrarily reduce the high cut-off frequency. Then, two low-pass filters consisting of the proposed unit cells are designed and simulated. To further verify the proposed procedure, one of the filters is fabricated, whose measurement results are in good agreement with the simulation results. This filter provides a pass band of 5.6 to 6.3 GHz and has dimensions of 0.82λg×0.22λg. The proposed method has the potential to minimize microwave and terahertz devices.

Polarization-Insensitive and Oblique Incident Angle Stable Miniaturized Conformal FSS for 28/38 GHz mm-Wave Band 5G EMI Shielding Applications

This letter presents a miniaturized conformal dual-band mm-wave frequency selective surface (FSS) for fifth-generation (5G) electromagnetic interference (EMI) shielding applications. Two back-to-back resonators are separated with a 0.254 mm thin dielectric substrate. The proposed FSS exhibits two wide stopbands (S21<-10 dB) in the mm-wave 5G frequency spectrum. The stopband bandwidths (BW) are 42.8% at 28 GHz and 24.2% at 38 GHz. The periodicity of the unit cell is 0.26 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , where λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> is the wavelength of the lower stopband. The key features of the proposed FSS include a miniaturized unit cell structure for 28 GHz and 38 GHz frequency bands with a high oblique incident angle (OIA) stable filter behavior up to 60°. The proposed FSS also features polarization insensitivity and conformality. The simulated and measured results show good agreement for EMI shielding applications.

A miniaturized quintuple-band frequency selective surface based on enclosed cross slots

Abstract This article presents a low-profile quintuple-band frequency selective surface (FSS) that is designed as a sub-reflector for applications including satellite systems (C band), EPR (electron paramagnetic resonance) spectrometers, motion and traffic light crossing detectors (X band), Direct Broadcast Satellite and broadcasting satellite service (Ku band), and shortrange applications (K band). The dimensions of the miniaturized unit cell 0.08λ0×0.08λ0×0.012λ0, where, λ0 is the free-space wavelength corresponding to the lower cut-off frequency. There are five stop bands, and frequencies at which they resonate are 6.3, 7.06, 9.30, 11.2, 14.0, and 18.64 GHz. The fractional bandwidths (FBW) of these bands are 62.6, 7.5, 9.2, 11, and 11.69%, respectively. Additionally, as a result of the structure’s four-fold symmetry, it exhibits a good polarization-insensitive response as well as a stable response in both the TE and TM modes. Full-wave simulation is performed on the structure, after which an equivalent circuit model is constructed.

Convoluted Meander Line-Inspired Metallic Surface Filter for Bluetooth and WLAN Bands

A convoluted meander line integrated cross dipole metallic structure with a dual-bandstop feature is presented in this manuscript. The investigated frequency-selective surface (FSS) exhibits the bandstopping characteristics for the Bluetooth (2.4 GHz) and WLAN (5.5 GHz) applications with a miniaturized unit cell size of 9.7 × 9.7 mm2. The proposed design has a polarization insensitivity feature for the TE and TM polarized waves’ incidents at 0°–60° with an interval of 15° angle. The equivalent circuit model of the presented FSS unit cell is also discussed and their limped element values are presented. The FSS design has a compact size which makes it favorable for low-profile band-filtering systems and multipath EM wave’s insensitivity. The suggested FSS configuration has good correspondence with modelled and measured results.

Low-cost laser cutting fabricated all-metallic metamaterial near-field focusing lens

In this work, a low-cost all-metal metamaterial near-field lens based on laser cutting technology is proposed. A novel spiral-slot structure is proposed to achieve miniaturized unit cells with an adjustable 360-degree phase shift at a length smaller than 0.2 times the operating wavelength. Since the unit is entirely constructed of stainless steel, it is resistant to high temperatures and high pressures compared to existing results. Moreover, a four-layer structure is used to increase the transmission coefficient. The final L-band near-field lens is constructed of 20 × 20 units. Simulation and measured results show that the half-power beamwidth of the focus is less than 211 mm from 1.52 GHz to 1.68 GHz at the focal spot observation plane of 500 mm from the lens. Since numerically controlled machine tools and three-dimensional printing are prohibitively expensive for machining large metal components, a low-cost all-metallic lens was manufactured using laser cutting technology. The measured results are in agreement with the simulation results.

Design of a Compact Single-Layer Frequency Selective Surface With High Oblique Stability

In this article, a compact single layer band stop frequency selective surface (FSS) with superior resonant stability is presented. The proposed FSS unit comprises of a symmetrically modified square loop. The square loop has been modified in order to increase the perimeter. Moreover, modified square loop is arranged in C4 rotational symmetry to ensure the polarization independence. The designed FSS exhibits highly stable response for the incident angle variation from 0° to 86°. At the resonant frequency of 5.54 GHz, its miniaturized unit cell size is 0.09 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ₀</i> × 0.09 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ₀</i> and the thickness is only 0.007 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ₀</i> . The operating phenomenon of this FSS is explicated by analyzing the equivalent circuit model, electric field and surface current distributions at resonant frequency. A test sample of the designed FSS has been constructed for the validation purpose. The transmission coefficients response of the proposed FSS has been measured and found to be congruent with the simulated responses. The salient features that distinguish the proposed FSS design over others are low complexity, low thickness, compact unit cell and excellent angular stability.

Via-based miniaturized rasorber using graphene films

In this work, we present a miniaturized wideband rasorber with good angular stability using via-based metal–graphene structure. The rasorber consists of a compact lossy layer, a frequency-selective surface layer, and an air spacer in the middle. The metal–graphene structure in the lossy layer achieves a tiny period due to multiple metal vias connected with meander lines and open stubs. The graphene resistive films printed on the surface by screen-printing technology realize omnidirectional planar resistors for broadband absorption. The 1-dB transmission band of the rasorber is from 7.27 to 8.01 GHz and the 10-dB reflection band is from 2.54 to 8.58 GHz. Due to its miniaturized unit cell, both the transmission and absorption performance is stable with a large-angle incident wave. The ultra-miniaturized rasorber is fabricated and measured, which demonstrates a wide bandwidth of 108.6% and a small period of 0.05λL with great angular stability, making it a good candidate for bi-station stealth radome applications.

Multi beam scanning programmable metasurface using miniaturized unit cells for 5G applications

This paper proposes a programmable reflective metasurface with a miniaturized unit cell that actively controls the scattered waves for achieving steerable multibeam radiation in sub-6 GHz 5G communication systems. The design uses array theory to provide the required phase shifts for various multibeam radiation patterns. The reconfigurability of the metasurface phase profile is attained by voltage-controlled varactor diodes embedded in the structure. Then, different unit cell arrangements are employed to achieve multibeam functionality where Pianoboard and Chessboard configurations provide one and two-dimensional multi beams, respectively. It turns out steerable multibeam radiation is achieved by dynamically change the dimension of the super unit cells. The reliability of the results is verified through analytical and numerical approaches. Moreover, the comparisons show that the proposed unit cell has more miniaturized size rather than the conventional cells, resulting in a better approximation for the ideally continuous phase profile identified by the generalized Snell’s law.

A Miniaturized Frequency Selective Rasorber With Independently Regulated Selective Dual-Transmission Response

In this letter, a miniaturized-element dual-polarized frequency selective rasorber (FSR) with independently regulated dual-transmission response has been presented. The proposed FSR is made of two cascaded layers separated by an air spacer, where the top lossy layer provides wideband absorption along with in-band transmission and the bottom lossless layer exhibits a dual bandpass filter. The novelty of the proposed design lies in the use of lumped capacitors in the top layer to realize the independently controlled highly selective transmission frequencies as well as attain a miniaturized unit cell topology (having dimensions of 0.08 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> × 0.08 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> , λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</sub> being the lowest operating frequency). In addition, convoluted slot geometries are patterned in the bottom layer to obtain the transmission bands appearing at the same frequencies as that of the top layer. The proposed structure has an operating range of 1.87–7.97 GHz, whereas two distinct transmission responses are located at 3.52 and 5 GHz having insertion losses of 1.2 and 0.82 dB, respectively. Furthermore, the geometry exhibits an angularly stable performance upto 40° for both TE and TM polarizations. A prototype of the proposed FSR was fabricated and measured to validate the simulated responses under normal incidence.

A Simultaneous Beam Steering and Polarization Converting S-Band Transmitarray Antenna

In this paper, a multi-functional transmitarray antenna consisting of miniaturized unit cells for S-band radar applications is proposed. The unit cell size is 0.4λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> × 0.4λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> , and it is composed of a receiving (Rx) antenna, a miniaturized inductively-loaded reflection-type phase shifter, a PIN diode switch for polarization conversion, and a dual-polarization transmitting (Tx) antenna. The types of Rx and Tx antennas are coupled-fed stacked patch antennas. The designed reflection-type analog phase shifter has a 36 % smaller area than the conventional reflection-type hybrid coupler-based phase shifter. It has a 3-bit phase-shifting capability realized with a 0 ~ 330° analog phase shifting. The designed SPDT PIN diode switch can select the polarization of the transmitted wave and accept a high input RF power of 23 dBm. The proposed 8 × 8 transmitarray antenna with F/D of 0.33, made from its unit cell, has a gain of about 7.9 dBi and performs 90° 2D beam steering for vertical-to-horizontal and vertical-to-vertical polarization conversions at the center frequency.

S-대역 레이다용 소형 다기능 투과형 메타표면 단위셀 설계 및 검증

In this study, miniaturized unit cell design and verification of multi-functional transmissive meta-surface for S-band radar are presented. The proposed unit cell comprises a receiver (Rx) antenna, a miniaturized reflection-type phase shifter, a PIN diode switch for polarization selection, and a dual-pol transmitter (Tx) antenna. The Rx/Tx antennas are stacked patch type antennas, and the reflection-type phase shifter, which has a smaller area of 36 % than a conventional hybrid coupler, controls the phase shifting from 0 to 330°. The PIN diode switch uses a −5 V reverse DC voltage bias to handle high input radio frequency (RF) power of 23 dBm. Moreover, a 1×2 unit cell array was fabricated to verify the unit cell performance. The array antenna freely converted polarized waves (horizontal/vertical) and exhibited beam steering performance in a range of approximately 50°.

A Novel Fractal Inspired Iterated Four-Legged Loaded Loop Elements Based 2.5-D Miniaturized Frequency Selective Surface

This letter presents a 2.5-D frequency selective surface (FSS) based on four-legged loaded loop elements of third-order iteration inspired by fractal geometries. This FSS design strives to harness the efficacy of the space-filling property of fractals and an additional degree of freedom associated with the use of metal vias in planar structures to obtain a miniaturized unit cell by enhancing the electrical length altogether. The proposed FSS provides a band-stop response with resonance at 1.056 GHz and demonstrates identical transmission curves for transverse-electric and transverse-magnetic modes of polarization of the incident wave. The unit cell of the proposed FSS achieves a figure-of-merit <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$({{{\rm{\lambda }}_{0}}/{\rm{P}}{\boldsymbol{\ }}}){\rm{\ = \ 29}}$</tex-math></inline-formula> , where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{\rm{\lambda }}_{0}}$</tex-math></inline-formula> is the free space resonant wavelength and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> is the periodicity exhibited by the unit cell, and offers an excellent angular stability up to 75° for oblique incidence. The measured results advocate the real-time shielding effectiveness of the fabricated prototype.

2.5-D Partially Reflective Surface for Resonant Cavity Antennas: Design and Synthesis

A new concept of 2.5-D partially reflective surface (PRS), with its potential applications in the design of resonant cavity antennas (RCAs), is presented. The proposed structure is in the form of a closed circular loop in which a pair of orthogonally split circular rings, printed on both sides of a substrate, is connected in series by four vertical vias to constitute the 2.5-D PRS unit cell. The 2.5-D PRS has a miniaturized unit cell size, in terms of wavelength, enabling the placement of a large number of unit cells in a given small area, and offers the flexibility of arranging those unit cells in different configurations. The unit cells are arranged in this work in a tapered configuration to construct the PRS. Based on the tapered 2.5-D PRS, a circular aperture RCA with an aperture area of 2.04λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ( λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> being wavelength at the center frequency of 4.2 GHz) is designed, fabricated, and measured for its input reflection coefficient and radiation patterns. The prototype antenna yields a peak realized gain, 3 dB gain bandwidth overlapping with the impedance bandwidth, and an aperture efficiency, respectively, of 13.7 dBi, 26.2%, and 91.6%.

Polarization insensitive multilayered broadband absorber for L and S bands of the radar spectrum

AbstractDesigning a low frequency broadband absorber is a nontrivial task in terms of establishing a trade‐off between overall absorber thickness, wide absorption bandwidth, and miniaturized unit cell size. To address the issue, we propose a novel broadband absorber design based on multilayered configuration, which covers the lower bands of the radar spectrum. The design is implemented using resistive ink patterns that are printed on an economical FR4 substrate. The reflectivity response of the proposed broadband absorber is less than −10 dB in the frequency range 1.26 to 4.38 GHz, covering the L and S bands of the radar spectrum with a fractional bandwidth of 110.63%. Furthermore, the structure has a miniaturized unit cell of dimension 0.057λL and a notable small thickness of 0.079λL. The implementation of the equivalent circuit model further validates the proposed design. The design is fabricated and experimentally verified. The simulation and measured results are in good congruence with each other.

Generation of Multiple Pseudo Bessel Beams with Accurately Controllable Propagation Directions and High Efficiency Using a Reflective Metasurface

In this paper, a generation method procedure based on a reflective metasurface is proposed to generate multiple pseudo Bessel beams with accurately controllable propagation directions and high efficiency. Firstly, by adjusting the miniaturized unit cell of the reflective metasurface to modulate the electromagnetic waves using the proposed method, some off-axis pseudo Bessel beams with different propagation directions are generated. Then, by achieving the large-angle deflection and comparing the results with previous existing methods, the superiority of the proposed method is demonstrated. Based on the generated single off-axis pseudo Bessel beam and the superposition principle of the electromagnetic wave, a reflective metasurface with 47 × 47 elements is designed and fabricated at 10 GHz to generate dual pseudo Bessel beams. Full-wave simulation and experimental measurement results validate that the dual pseudo Bessel beams were generated successfully. The propagation directions of the dual pseudo Bessel beams can be controlled accurately by the reflective metasurface, and the efficiency of the beams is 59.2% at a propagation distance of 400 mm. The energy of the beams keeps concentrating along the propagation axes, which provides a new choice for wireless power transfer and wireless communication with one source to multiple receiving targets.

Angularly Stable Frequency-Selective Surface Using Shifted Double-Sided Screens

In this letter, a shifted double-sided frequency selective surface (FSS) with miniaturized unit cells is proposed to achieve superior performance in angular insensitivity. Two identical FSS screens mounted on both sides of a thin substrate have lateral displacement relative to each other. We shed light into effect of shifting by investigating current and field distributions, and present the operating principles of the proposed FSS along with the equivalent circuit model. The whole structure has a lower profile (a thickness of 0.001 λ , where λ represents the resonant wavelength in free space) as well as a small size (0.043 λ × 0.043 λ ). This FSS as a bandpass spatial filter is stable with respect to different polarizations, polarized angles, and incident angles of the illuminating waves. A prototype of the proposed FSS is fabricated and tested. The measured frequency responses agree well with the simulated results.

High-$Q$ Terahertz Absorber With Stable Angular Response

This article presents a narrow-band terahertz absorber using miniaturized unit cells. The absorber is made of three metallic layers separated from each other using low-loss cyclic olefin copolymer as dielectric spacers. A high quality factor ( $Q$ ) is obtained using a first-order resonating structure with additional capacitive loading formed by the top two metallic layers. A circuit model is developed for the analysis and design of the proposed absorber. The designed absorber shows $\text{1}\%$ fractional bandwidth for more than $\text{90}\%$ absorption around a center frequency of 0.5 THz under normal incidence angle. This is equivalent to a quality factor of $Q=31$ , calculated at $\text{50}\%$ absorbance. The structure shows a highly stable absorbance over a wide range of oblique incidence angles. The designed absorber has been fabricated using a microfabrication process. The measured results of the fabricated prototype are in good agreement with the simulations.

Ultrathin and Miniaturized Frequency Selective Surface With Closely Located Dual Resonance

Ultrathin and miniaturized frequency selective surface (FSS) with closely located dual bands is proposed in this letter. The proposed FSS comprises parallel patches and meandering lines that construct parallel LC resonators. Then, two independent passbands can be achieved and adjusted by only changing corresponding structure parameters of the element. Through a catercorner arrangement, the structure avoids the effect introduced by the unnecessary inductance. The proposed FSS resonates at 1.59 and 1.96 GHz with a low resonant frequency ratio of 1.23. The proposed FSS provides a low profile of 0.13 mm and a miniaturized unit cell size as compact as 0 . 042λ × 0 . 042λ. A simplified equivalent circuit model is established, which provides good insight into the operation mechanism. Finally, a prototype of the proposed structure is fabricated and measured. All the results present excellent resonant stability with respect to different polarizations and incident angles up to 60°.

Single layer miniaturized ultra-thin FSS with five closely spaced bands

AbstractThis Paper reveals a novel single layer five band frequency selective surface (FSS). Novelties of the proposed FSS lie in its five closely spaced stop bands at 2.4, 3.38, 4.82, 6.32, and 7.75 GHz as well as the reduced single layer structural thickness (0.0016 λ0) and the miniaturized unit cell size (0.0656 λ0) at lower resonant frequency as compared to the existing multiband FSS. The unit cell structure consists of six octagonal concentric interconnected loops. Adjacent loop interconnection technique reduces the cell size by more than 44%. Furthermore, arrow-shaped rings are also introduced on each corner of the outermost octagonal loop, and using this technique approximate 23% cell miniaturization can be achieved. In addition, the proposed FSS exhibits excellent angular stability.