Design of frequency selective surface based on Minkowski fractal and interdigital capacitance

A novel miniaturised frequency selective surface (FSS) unit cell is proposed based on the Hilbert fractal and 2.5-dimensional (2.5-D) metallic loop. For the increase of current path, both sides of substrate are used which are connected together by four vias. The dimension of FSS unit cell is obtained as 0.041λ0 × 0.041λ0 at the frequency of 2.47 GHz. The transmission coefficient is insensitive and independent of angle and polarisation of incident wave. A prototype model of the proposed FSS is fabricated and measured for the proof of concept. It is shown that it achieves better miniaturisation relative to the FSS reported in the literature.

This paper, proposed a frequency selective surface (FSS) with triple band-stop characteristics. The structure demonstrated can be effectively used to shield different scientific and technical applications from unwanted electromagnetic radiation. The compact unit cell consists of a cross-loop surrounded by a dodecagon. The overall dimensions of unit cell are 22 mm × 22 mm. The substrate material is RO-3003 with a dielectric constant (\(\varepsilon_{\text{r}}\)) 3 and thickness 60 mil. The dimensions of each unit cell have computed by the lowest cutoff frequency. This FSS structure is designed for the rejection of three frequency bands, 5.5 GHz, 3.5 GHz and 2.4 GHz, respectively. The proposed FSS structure provides preeminent electromagnetic shielding because of its polarization insensitivity and triple-band absorption.

This work proposes a frequency‐selective surface‐based radome structure to selectively allow the radar altimeter operating band and also minimize the interference from Sub‐6GHz 5 G frequency bands. A Jerusalem cross and combinational loop (JCL) based frequency selective surfaces (FSS) unit cell of overall dimension 0.37λ was synthesized using a thin flexible substrate for use in fuselage of airborne systems. The proposed FSS unit cell exhibits transmission zero at 3.61 and 6.025 GHz and highly selective pass band at 4.3 GHz. The effect of bends and angle of incidence on the frequency response of the synthesized FSS was studied in transverse electric and transverse magnetic modes. A lumped element‐based equivalent circuit model for the proposed design was also presented. Finally, the fabricated prototype was experimentally validated in an Anechoic chamber setup and the suitability of the proposed FSS layers for aviation radar systems was confirmed.

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.

Wave concept iterative procedure (WCIP) is used for the determination of scattering characteristics of single and double metallic ring frequency selective surfaces (FSS). In the WCIP method, the analysis of the FSS is reduced to that of the unit cell. Basically, the WCIP method consists of scattering the incident waves at the interface and the reflection of the scattered waves by the closing ends of the periodic wall box containing the FSS unit cell. The use of the two dimensional fast Fourier transform algorithm results in a reduction of the running time and memory space. FSSs based on single and double metallic rings are analyzed by the WCIP method. A good agreement is observed between the WCIP results and the experimental results. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 1324–1328, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23383

A patch-slot-patch frequency selective surface (FSS) exhibiting bandpass response is proposed in this paper. The FSS unit cell is composed of two cross-dipole shaped patches and a cross-dipole shaped slot in between. The proposed FSS exhibits bandpass response with two closely spaced transmission poles around 3 GHz and 3.5 GHz. A 3-dB transmission bandwidth of upto 20% is achieved for the FSS. The proposed design has a thickness on the order of 0.032 λ <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> . The paper presents with parametric studies how the poles can be tuned individually. The transmission phase of the FSS varies linearly towards zero with frequency that makes the FSS useful in designing Filter-Antenna when placed as a superstrate above a broadside radiator.

CPW-fed dual-element metamaterial inspired multiband antenna using simple FSS for gain enhancement

In this paper, frequency selective surface (FSS) with relative zero-phase shift is realized and characterized. The FSS unit cell is designed by adding cross aperture to the cross loop slot at its center, and the four ends are placed by Y-shaped slots. Compared with normal FSS, the FSS with the relative zero-phase shift avoid the aberrance of the main lobe direction on the radiation pattern of antenna, when the FSS is designed for the radome. Numerical simulations are carried out to validate wider bandwidth and better angle stability. It is a miracle that the epsilon-near-one(ENO) metamaterial properties are presented, so the screen of these FSSs have many properties similar to air. The near-field and far-field are almost not affected by the screen for the cylindrical wave.

Uniformity improvement of microwave heating with switchable frequency selective surface

In this paper, a new geometrical shape of the bandpass modified circular ring frequency selective surface (FSS) structure with significant electrical response such as angular stability up to $$50^{\circ }$$50? of the angle-of-incidence (AOI) for both the perpendicular (TE) and parallel (TM) polarized waves has been discussed. The geometrical parameters of the proposed bandpass FSS is obtained by the transformation of bandpass single square loop FSS structure parameters. To achieve the frequency response of the proposed bandpass structure, commercially available 3D electromagnetic simulators such as CST Microwave Studio and Ansoft HFSS are used. The proposed bandpass FSS structure provides significant angular (i.e., up to $$50^{\circ })$$50?) and polarization (i.e., perpendicular and parallel) stability as compared to that of various other reported literatures. In addition to this, one of the important characteristics of the resonant structure is the quality factor (Q-factor), which has also been discussed for the proposed bandpass FSS structure at different AOI.

The design, analysis, and measurement of a 90° polarization converting frequency selective surface (FSS) are implemented for incident wave polarized in arbitrary azimuth angle. The FSS unit cell is achieved by two orthogonally arranged monopole-coupler-monopole (MCM) module pairs. The incident linearly polarized (LP) wave is polarized along $u$ -axis of the local orthogonal coordinate system ( $\boldsymbol{u}, \boldsymbol{v}, \boldsymbol{z}$ ), it can be effectively converted into a wave polarized along $\boldsymbol{v}$ -axis, where the azimuth angle between ${\boldsymbol{u}-}$ and $\boldsymbol{x}$ -axis of ( $\boldsymbol{x}, \boldsymbol{y}, \boldsymbol{z}$ ) coordinate system is arbitrary. The polarization conversion mechanism is explained by the fact that the decomposed components along ${\boldsymbol{x}-}$ and $\boldsymbol{y}$ -axis of the incident wave are independently converted into ${\boldsymbol{y}-}$ and $\boldsymbol{x}$ -axis, respectively, by the co-orientated MCM modules, and then combined into a wave polarized along $\boldsymbol{v}$ -axis in the outgoing wave space. A prototype of the polarization FSS is fabricated and measured. The measured results have good agreement with the simulated ones.

This communication presents a hybrid frequency selective surface (FSS) and rectenna design for wireless power harvesting. To this extent, the center of the original FSS structure acts as a probe-fed patch antenna and an additional layer was added to the rear of FSS structure to mimic the required antenna ground plane, while minimizing its impact on FSS performance. The proposed hybrid solution yields a bandpass frequency response at GSM 900-MHz frequency band, with band reject behavior at 2.4 GHz and, on the other hand, act as a energy harvesting system through the antenna element at the 2.4-GHz ISM band, e.g., for recycling ambient Wi-Fi energy. The developed prototype, consisting of an array of 12 unit cells, was able to power a 56-mW LED at a 2-Hz rate from an incident power level of -10 dBm, resulting in an average output power of 300 μW and an unit cell RF-DC conversion efficiency of 50%.

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 wideband frequency selective surface (FSS) absorber implementing lossy ink layer for electromagnetic absorption is presented in this paper. The absorber is designed on a metallic ground plane which acts as reflector. A thin layer of lossy ink material is used in the form of double square loops which serves as an absorber at the top surface of the substrate. The FSS unit cell has an overall size of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$18\mathbf{mm x }18\mathbf{mm x }0.8\mathbf{mm}$</tex> with outer and inner square loops whose dimensions are 15mm and 10 mm, respectively. The results show that the proposed absorber operates between 8 GHz to 14 GHz covering X and lower Ku bands. It is shown that this design provides a fractional bandwidth of 54.5% and 98% absorptivity in the whole band. The wideband and high absorptivity of the proposed FSS absorber demonstrates its potential for electronic warfare and other strategic applications.

In this article, a novel and compact Frequency Selective Surface (FSS) with dual-band pass characteristics is proposed. The proposed design of the FSS unit cell is composed of two concentric rings with slotted stubs connected to the outer side of each. The proposed FSS structure provides a dual band-pass characteristic with operating frequencies of 7.5 GHz and 9.8 GHz having a bandwidth of 1.4 GHz for both bands. Both operating bands can be controlled independently by varying the design parameters of the structure. The structure is insensitive to oblique incidence angles up to 60 degree. Further, the geometry is low profile and angular stability and polarization are stable. The proposed design finds very promising applications in C and X bands.