Polarization and Frequency-Selective Surface for Vehicular Beamforming Communications Requiring Near-Zero Profile

This letter presents the design and testing of a novel triple-layer frequency selective surface (FSS) with ultraminiaturization for electromagnetic shielding applications. The proposed unit cell is constructed using meandered lines running along the three layers and they are interconnected using metalized vias to increase the electrical length of FSS. The FSS is designed to offer band stop resonance at L-band frequency with a foot-print of 0.022 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> × 0.022 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> with a thickness of 0.006 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> and it provides at least 38% of miniaturization in comparison with similar literature. To validate the transmission performance, a prototype FSS with a periodicity of 6 mm is fabricated. The FSS consists of 2500 elements arranged in a 50 × 50 square lattice. The transmission performance of the proposed FSS is verified using simulation and experiment. The proposed FSS has rotational symmetry and hence it is polarization insensitive. Furthermore, the FSS offers excellent angular stability up to the maximum incidence angle of 60° under both transverse electric and transverse magnetic modes of operation. The proposed FSS can be used for shielding applications in global positioning systems tracking and aircraft surveillance systems.

Miniaturized frequency selective surfaces (FSSs) have been intensively investigated because of the space limitation in practical applications, such as wireless communication system working at low frequencies. Loading lumped capacitor is an effective miniaturization method to achieve the unit cell size as compact as λ 0 /15 (λ 0 refers to the resonant wavelength in free space) [1, 2]. But this approach requires bulk components which increase the complexity and cost of fabrication. Also, the tolerance of lumped elements makes it a challenge to maintain a stable resonant performance. Another effective method of reducing the unit cell size is to adopt convoluted elements which perform well in conforming to curved surface [3–5]. This method not only improves the angular stability of the frequency responses, but also moves the operating band away from the grating region which is determined by the periodicity of the array. The convoluted structures can reduce the FSS dimension because of their space filling property [5]. Therefore, their miniaturization potential will be restricted by the element area determined by the periodicity. To address this problem, the double layered convoluted structures, which make use of the element areas on both sides of substrate, are presented in this work to further miniaturize the FSS unit cell. Fig. 1 shows the geometry of the proposed bandpass FSS, which consists of a convoluted square slot loop and a convoluted capacitive element arranged on each side of the substrate. The top layer acts as a parallel LC resonator and the bottom layer acts as a capacitor. The LC resonator and the capacitor are connected in parallel. Therefore, the proposed bandpass FSS operating at 2.5 GHz provides the unit cell dimension as small as λ 0 /23 because of the increased capacitance of the unit cell. On the other hand, a double layered convoluted structure for the bandstop FSS is also proposed as shown in Fig. 2. It is seen that the top and bottom layers are connected by metallic via to construct a closed loop, which results in an increased inductance of the unit cell. Consequently, the element size of the presented bandstop FSS resonating at 2.5 GHz is only λ 0 /22. In addition, all the presented FSSs exhibit good performance of resonance stability with respect to different polarizations and incident angles.

본 논문은 결함 모드 특성을 갖는 주파수 선택적 표면에 의한 WCDMA에서 동작하는 안테나의 이득 향상을 위한 설계와 제작에 대해 다룬다. 제안된 결함 모드 특성을 갖는 FSS 단위 셀은 동일한 크기의 일반적인 단위 셀보다 낮은 주파수 대역에서 적용이 가능하므로 단위 셀의 크기를 66 % 정도 축소시키었다. 단위 셀의 최적화 된 배열 개수는 <TEX>$13{\times}13$</TEX>으로 하였으며, WCDMA 송신 대역과 수신 대역에서 동작하는 패치 안테나를 각각 설계하였다. 사각형 구조의 단일 패치 안테나를 사용하여 WCDMA 대역을 포함한 동작 특성을 나타내도록 하였다. 모의 실험한 결과, 송신 대역에서 제안된 FSS-1 복합체 구조(송신 대역의 패치 안테나와 FSS)의 이득은 9.98 dBi에서 13.28 dBi로 3.3 dB 향상되었다. 수신 대역에서 제안된 FSS-2 복합체 구조(수신 대역의 패치 안테나와 FSS)의 이득은 9.81 dBi에서 15.34 dBi로 5.53 dB 향상되었다 측정 결과 제작된 FSS 복합체 안테나는 약 337 MHz(<TEX>$1.87{\sim}2.21GHz$</TEX>)의 대역폭을 가지며 1.95 GHz에서 11.39 dBi, 2.05 GHz에서 13.11 dBi, 2.14 GHz에서 11.09 dBi의 이득을 나타내었고, 방사 효율은 81 %임을 확인하였다. 제안된 FSS 복합체 안테나는 높은 이득을 갖기 때문에 WCDMA 중계기 시스템에 응용될 수 있을 것으로 사료된다. In this paper, FSS(Frequency Selective Surface) using defect mode characteristic is proposed. The unit cell using defect mode characteristic of the proposed FSS is offered lower resonant frequency in the same cell size. The number of suitable array is optimized 13 by 13. Also, the patch antennas operated in WCDMA(Wideband Code Division Multiple Access) Tx band and Rx band are designed for the comparison. The gain value of proposed FSS-1 complex structure (the patch antenna of Tx band and FSS) is improved 3.3 dB from 9.98 dBi to 13.28 dBi in Tx band. The gain value of proposed FSS-2 complex structure(the patch antenna of Rx band and FSS) is improved 5.53 dB from 9.81 dBi to 15.34 dBi in Rx band. Also the measured impedance bandwidth(<TEX>$VSWR{\leq}2$</TEX>) of manufactured <TEX>$13{\times}13$</TEX> array antenna is from 337 MHz(1.87 to 2.21 GHz). The measured radiation gain is 11.39 dBi(1.94 GHz), 13.11 dBi(2.05 GHz), 11.09 dBi(2.14 GHz). The measured radiation efficiency is 81 %. Because the proposed FSS structure has more higher gain, it will be applied to antenna of WCDMA repeater system.

In this paper, the Minkowski fractal is used to design the geometry of a frequency selective surface (FSS) unit cell, which resembles the shapes found in nature. The proposed FSS unit cell has both angular and polarization stabilities of incident wave. For the miniaturization of FSS and decrease of resonance frequency, interdigital capacitances (IDCs) are devised in the FSS structure, which do not eliminate angular and polarization stabilities. The dimensions of the unit cell are 5 mm × 5 mm and miniaturized 0.095λ0×0.095λ0. The resonance frequency is specified as 5.75 GHz with 155 MHz bandwidth. An equivalent circuit is derived for the unit cell to evaluate its frequency responses. The effects of variations of the geometrical dimensions of the FSS unit cell on its performance are studied. A prototype model of proposed FSS is fabricated and measured. The performance of its full-wave computer simulation results and measured data are compared and are shown to be in good agreement.

This paper describes a millimeter-wave thin lens that exhibits different beam-shaping characteristics depending on the polarization of the incident waves. The proposed unit cell topologies, which use multiple rectangular patches and rectangular-slotted grids, enable thinner (= 0.05λ 0 ) and smaller (= 0.168λ 0 ) features than in previous polarization-dependent lenses. An appropriate set of the proposed unit cells is shown to cover a tunable phase range of 180° with respect to one polarized wave but have an almost-zero tunable range of phase shifts with respect to another polarized wave. Thus, using this unit cell set for x-polarized incident waves, the proposed lens operates as a convex lens, whereas for y-polarized incident waves, the lens operates as a frequency selective surface. This confirms that gain variations of 13 dB or more can be differentiated according to the polarization of the incident waves on the lens, supporting polarization-dependent beam-shaping capability as a function of the polarization of incident waves.

Frequency Selective Surface (FSS) is a specialized structure used in the field of electromagnetic waves and radio frequency (RF) engineering. It is designed to exhibit selective transmission or reflection properties based on the frequency of the incident electromagnetic waves. This article describes the design, construction, and analysis of a textile-based band-stop frequency selective surface for use in the highly EM-polluted GSM, Wi-Fi, LTE, and WiMAX bands. A full-wave EM solver called CST Microwave Studio was used to develop and simulate the unit cell of the proposed FSS at the relevant frequency. In this study, embroidered and screen-printed textile based FSSs were designed. According to the results of this study, it was demonstrated that both embroidery and screen printing FSSs exhibit resonance at a frequency of 3.5 GHz. The screen printing method yielded the best results in terms of resonance frequency sensitivity, while the embroidery method showed a resonance frequency shift. It was observed that the stitch directions and density are important parameters in the embroidery method. Gaps between the embroidery paths in the production of embroidered FSSs resulted in differences from simulations due to the disruption of the structural integrity of the unit cell. Consequently, textile-based FSSs offer advantages over traditional FSSs. This study highlights the potential of textile FSSs as an effective means of reducing electromagnetic pollution, and suggests that further improvements in the design and production processes of textile FSSs can be made.

In this paper, a modified frequency selective surface (FSS) is proposed for cloaking of a dielectric cylinder. To this end, the needed value of surface reactance (X <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> ) of the FSS structure to eliminate scattering coefficient of the dielectric cylinder, is analytically calculated; the obtained value is 195 Ω. The modified double slot square loop unit cell, is designed to realize the calculated value of z <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> . A dielectric cylinder with radius 12.45mm and height 180mm is covered with the array of the designed unit cell. Scattering width and electric field distribution of the dielectric cylinder with and without the designed FSS structure are obtained by CST software. Based on the simulation results, the total (SW) of the dielectric cylinder with the proposed FSS structure is about 0.88, which is about 10 units lower than that of value in uncloaked cylinder. The designed FSS is a suitable structure in dielectric cylinder cloaking applications.

In this paper, we present three ultra-thin frequency selective surface (FSS) microwave absorbers on a single layer, that have three remarkable features. First, the various absorbing bandwidths can be obtained in our absorber by adjusting the two absorbing peaks, which are produced by two different resonance effects on the FSS. By manipulating the dimension parameters, we design the dual-band, 3-dB and 10-dB band absorbers. We achieved the absorber's thickness of $0.039\lambda_{\rm g}$ with the single layer due to high loss of inter-digital capacitor patterns on the FSS. Additionally, the proposed absorbers are insensitive to polarized electromagnetic (EM) waves because of the symmetric structure of the FSS. In this study, the absorber mechanism and transmission line (TL) modeling for the absorber design are studied. Each of the proposed absorbers is analyzed by using the TL equivalent circuit model and full-wave analysis. The loss factor is studied in order to demonstrate the origin of losses, and a parametric study is conducted to explain how to vary the absorbing bandwidths. The performances of each proposed absorber are also experimentally demonstrated.

In this study, the frequency selective surface (FSS), absorbance and sensing applications of new unit cells comprised of single, double and quad U‐shaped metallic elements are numerically and experimentally investigated. The numerical results are realised by using finite integration technique‐based electromagnetic simulation software, CST Microwave Studio. Experimental results are obtained by means of Agilent N5234A PNA‐L vector network analyser. The simulated and measured results of U‐shaped FSSs are carried out by using two different ways; periodic unit cell and waveguide boundary conditions. The single and quad U‐shaped FSS elements show a single band‐stop filter property, whereas the double U‐shaped FSS shows a dual‐frequency band‐stop filter behaviour. Absorber and sensor applications of the proposed U‐shaped FSSs are illustrated both numerically and experimentally. The three types of U‐shaped FSS structures show a narrowband absorbance which has potential in biomedical and sensing applications. Single and dual absorber characteristics are observed with a 90% absorbance. For the sensor configuration, 800 MHz bandwidth is obtained for sensing different materials showing that it is possible to realise different microwave sensor studies in industries of food and agriculture. Simulated and measured results are compared for FSS, absorber and sensor configurations, and the results show a good agreement with each other.

Raman scattering is a powerful technique for quantitatively probing high temperature and high speed flows. However, this technique has typically been limited to clean hydrogen flames because of the broadband fluorescence interference which occurs in hydrocarbon flames. Fluorescence can also interfere with the Raman signal in clean hydrogen flames when broadband UV lasers are used as the scattering source. A solution to this problem has been demonstrated. The solution to the fluorescence interference lies in the fact that the vibrational Q-branch Raman signal is highly polarized for 90 deg. signal collection and the fluorescence background is essentially unpolarized. Two basic schemes are available for separating the Raman from the background. One scheme involves using a polarized laser and collecting a signal with both horizontal and vertical laser polarizations separately. The signal with the vertical polarization will contain both the Raman and the fluorescence while the signal with the horizontal polarization will contain only the fluorescence. The second scheme involves polarization discrimination on the collection side of the optical setup. For vertical laser polarization, the scattered Q-branch Raman signal will be vertically polarized; hence the two polarizations can be collected separately and the difference between the two is the Raman signal. This approach has been used for the work found herein and has the advantage of allowing the data to be collected from the same laser shot(s). This makes it possible to collect quantitative Raman data with single shot resolution in conditions where interference cannot otherwise be eliminated.

This paper presents a wide incident angle metasurface unit cell element applied to a reconfigurable intelligent surface (RIS) for beamforming and beam-steering applications in the 26 GHz frequency band from the fifth generation of mobile communications (5G) frequency range 2 (FR2). Each metasurface unit cell is based on a printed frequency selective surface (FSS) loaded with a varactor diode. The FSS-based structure is based on a circular loop at the top and a slot-based ground plane at the bottom resulting in a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\boldsymbol{0.25 \mathrm{x} 0.25 \lambda_{0}}$</tex> total area. The complete unit cell element encompasses four conducting layers, in which the first two ones form the FSS. RF chokes are printed at the middle layer to isolate the DC circuit, and the bias lines are routed at the fourth layer. The unit cell has been conceived using the full-wave electromagnetic solver ANSYS HFSS. Its numerical results demonstrate a reflection phase shift up to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$180^{\circ}$</tex> and reflection magnitude higher than 0.4 at the 26 GHz frequency band for incident wave angle from 0 to <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$50^{\circ}$</tex> . The proposed reconfigurable intelligent surface might be applied to future wireless communication systems, planar antenna reflectors, and vortex beam generation.

This paper presents a multi-functional frequency selective surface (FSS)based on varactor diode and PIN diode loading. It can be realized that when the varactor diode is not loaded with voltage and the PIN is in the on state, the frequency selective surface(FSS) exhibits strong transmittance at 4 GHz, and when the PIN is in the off state, the frequency selective surface(FSS) exhibits strong reflectivity at 4 GHz. In addition, when the PIN is turned on, stable transmission of electromagnetic waves in a wide frequency range from 1.37GHZ-5.66GHZ can be achieved by changing the capacitance of the loaded varactor diode.

The authors are thankful for the useful comments [1] on their letter [2]. The presented artificial magnetic conductor (AMC) is not composed of square but hexagonal unit cells. The referenced first paragraph of [2, Section II], “Planar AMC Design,” makes reference to a general behavior based on a very simple LC model for the unit-cell geometry. Generally, the unit cell can be considered a frequency selective surface (FSS) backed by a dielectric slab with metallic ground plane. To increase the bandwidth of an AMC, it is necessary to reduce the total capacitance C. When the distance between unit cells increases, the gap capacitance decreases. If this is the main capacitive element contributing to the total C, the bandwidth increases. This happens, for example, for the patch unit cell in [3, Table I], a work referenced by [1]. In [3], only one capacitive element is used to model the unit cell, and the objective is to maximize the bandwidth while preserving the resonance frequency. The point is that the total C of the unit-cell model has to be expressed as a series or parallel combination of capacitive elements (gap, parallel plates, fringing effects, etc.), which obviously depends on the geometry of such a unit cell. However, the geometry of the presented unit cell (formed by dipoles) is mainly inductive due to the narrow strips. The behavior of the presented unit cell is described in the third paragraph of [2, p. 616]. It is clearly mentioned that there are two main capacitive elements that contribute to the total C: coplanar C (or gap C) and parallel plates C. Moreover, it is stated that “in sum, the wider AMC operation bandwidth for smaller unit-cell size (W) of this novel design is due to both slightly increased L and more significantly C decreased values of the parallel LC equivalent circuit.” This does not contradict [1] since, according to Fig. 3 and Table I of [2], for smaller unit cell W, the distance between cells 2d (the gap) decreases, and so the gap capacitance.

Fractal geometries have been extensively implemented in the design of multiband antenna and frequency selective surface (FSS). For example, convoluted and Hilbert patch elements were first proposed to reduce the unit cell size of FSS (Parker and El Sheikh, IEE Proc.-H, 138, 19–22, 1991.) A fractal FSS with self-similar Sierpinski dipole array was shown to have two stop bands (J. Romeu and Y. Rahmat-Samii, IEEE Trans., AP-48, 1097–1104, 2000). However, its resonant frequencies are rather sensitive to incident angles and polarizations. Minkowski patch FSS and Sierpinski carpet fractals have been shown to provide two or three stop bands with dual polarization capability (J.P. Gianvittorio, et. al., IEEE Trans., AP-51, 3088–3096, 2003.) Recently miniature band-pass FSS with fractal antenna-filter-antenna arrays was designed and demonstrated with good frequency selectivity (S. Zheng, et. al., IEEE AWPL, 11, 240–243, 2012.) A dual band fractal FSS with a 3:1 reflection to pass band ratio and significantly improved resonant frequency stability was proposed by the author (T.K. Wu, Microwave Optical Tech. Letters, 54, 833–835, 2012).

The miniaturized frequency selective surface (FSS) obtained by connecting a number of limbs with two flexible adjustable transmission zeros is proposed in this paper. The proposed FSS has two transmission zeros on both sides of the passband. The effects of the geometrical parameters on the bandwidth of transmission zeros and pole are analyzed. Adjusting the numbers of the limbs in the FSS can make a great difference to the ratio of the frequencies of the two working transmission zeros, and the coupling between the adjacent FSS unit cells is used to adjust the ratio of the frequencies of the two working transmission zeros slightly. The simulated results show that the ratio of the frequencies of the two working transmission zeros has wide adjustable range. The effects of the ways to connect the limbs on the ratio of the frequencies of the two working transmission zeros are analyzed. The prototype of the FSS with two limbs is fabricated and tested to verify the feasibility of the proposed method. The measured results show that the FSS designed by the proposed method has good polarization and angel stabilities, and this proves the proposed way is effective. This FSS is a good candidate to isolate the communication systems with two working bands.