Dual Bandstop Research Articles

Design of a low profile and ultraminiaturized frequency selective surface with dual band-stop response

In this paper, a miniaturized dual-band frequency selective surface (FSS) for electromagnetic shielding applications is presented. The FSS unit cell provides band-stop response at the resonant frequencies of 0.95 GHz and 2.52 GHz. The FSS element is constructed by employing convoluted metal stripes that are positioned on both sides of the substrate. The proposed configuration enhances the electrical length of the resonator while maintaining its physical dimensions. Moreover, the unit cell of the FSS exhibits rotational symmetry, which enables polarization independent operation. The designed FSS structure demonstrates excellent miniaturization characteristics, with a cell size and thickness of 0.019 λ0 × 0.019 λ0, and 0.00048 λ0, respectively. The cell size and thickness are calculated at the lower resonating frequency of 0.95 GHz. In addition, the stability of the proposed FSS structure is observed for both the TE and TM polarizations across an incident angle range of 0° to 80°. The resonating behavior of the structure is elucidated with the help of electric field and surface current distribution. Experimental verification of the dual-band FSS is conducted through the fabrication of a prototype on a FR4 substrate. The measured transmission coefficients are in good agreement with the simulated response for both TE and TM modes. Compared with the dual-band FSSs previously reported, the proposed FSS has the significant advantages of low profile and miniaturization.

A modified Astable multi-vibrator-driven 3D chaotic circuit with Dual LC band stop filters

This work describes a proposed circuit design with three essential parts: an Astable Multi-vibrator (ASMV) source producing a square wave as the driving signal, a two-stage LC band stop filter selectively attenuating frequencies with a focus on suppressing high-frequency components, and an integrator combining outputs from the second and third stages. Using two extra feedback channels, a standard ASMV gains the ability to change the duty cycle of the square wave, effectively altering the amplitude and duty cycle of the ASMV output signal. The LC band stop filter is vital for reducing or blocking frequencies close to 650 Hz and allowing other frequencies to predominate in the signal. The output frequency of the proposed circuit is governed by its specific parameters and frequency response characteristics. The suggested three-dimensional chaotic circuit produces dynamic, complex chaotic attractors with a simple circuit complexity. The differential equations describing the circuit’s functioning were checked using MATLAB. Circuit working was verified using Keysight ADS simulation and validated by experimental measurement. The randomness of the state variables are verified using the NIST test.

A double-layered C-band frequency-selective surface bandstop filter for maritime communication

ABSTRACT In this paper, a dual-bandstop frequency-selective surface (FSS) implemented using a four-legged Minkowski square and s hexagonal ring is presented. The proposed FSS shows dual stopbands at 4.9 GHz and 7.1 GHz in the C band. The size of the unit cell is 0.36λ0 × 0.36λ0, which is designed on an FR4 substrate with a thickness of 1.6 mm and a loss tangent of 0.02. The frequency response of the bandstop FSS is verified using circuit simulation, and its optimised dimensions are determined at the desired frequencies of operation. The results reveal that the ratio of the two stopband frequencies can be adjusted over a wide range by properly selecting the geometrical parameters. The impedance bandwidths for S11< –10 dB of 0.9 GHz and 1 GHz have been realised at the lower and upper frequency bands, respectively. A prototype is fabricated and measurements show a reasonable agreement with the simulated results, thus validating the design concept. It has been shown that the proposed bandstop FSS exhibits excellent stability upto 60° at oblique incident angles in both TE and TM polarisations. This FSS is suitable for C-band maritime applications due to wide stopbands and highly stable angular operation.

Advances in the construction of photonic structures with dual stopbands and beyond

The advances in developing multiple stopband photonic structures are reviewed, which can help researchers to develop photonic structures with multiple stopbands and tackle the challenges to meet the demands for anticounterfeiting, etc.

A novel and compact ultra‐wideband printed monopole antenna with enhanced bandwidth and dual‐band stop properties

AbstractThis article introduces a novel and compact design of an ultra‐wideband (UWB) printed monopole antenna with an enhanced bandwidth and dual band‐stop performance. A modified π‐shaped slot has been inserted in the ground plane to exhibit a wide impedance bandwidth of 116% (ranging from 3.1 to 11.2 GHz), whereas dual stopband responses (at 3.5 and 5.5 GHz) are obtained by embedding three I‐shaped stubs and a pair of modified Γ‐shaped slits in the radiating patch. The proposed topology is highly compact having an overall dimension of 18 mm × 14 mm (which is equivalent to 0.7λg × 0.54λg, where λg is the guided wavelength corresponding to the lower resonance band), has a low fabrication cost, an ultra‐wide impedance bandwidth, and omnidirectional radiation patterns in the H‐plane, which make the antenna appropriate for wideband applications and integration into UWB system. To check the advantages of the proposed antenna, experimental verification has been carried out as well as the results are compared for UWB scenarios.

Double‐Sided Indium Tin Oxide Photonic Crystal Glazing for All‐In‐One Multifunctional Rigid and Flexible Windows

AbstractFuturistic and high‐performance windows are required to perform multiple functions, occasionally including photo‐ and electricity‐associated functions. For each function, suitable components must be added, but this might result in complicated window structures that can impede the basic window function: high visibility. Therefore, platform technology is necessary to simplify window structures with minimal components for basic functions while adding specific desirable functions. This study proposes non‐close‐packed indium tin oxide (ITO) photonic crystals coated on both sides of rigid and flexible windows. Their photonic bandgap frequencies (stopbands) are tunable through the modulation of the ITO thickness or lattice constant, thereby manipulating the window light transmittances. When the stopband lies in bluelight (400–500 nm), the window can simultaneously block the bluelight and exhibit high transmittance (antireflection function) at 500–1500 nm. The dual functions are enhanced with double‐sided photonic crystal windows: the optical contrasts in solar irradiance transmittances (ΔTsol) between 500–1500 and 280–500 nm are maximally 37.1% and 47.2% for the glass and polyimide windows, respectively. Additionally, the windows can have dual stopbands. Moreover, the window stopbands can enhance the photoluminescence intensities of quantum dot films. This simplistic window is applicable to houses/buildings, automobiles, electronics, displays, and energy industries.

An ultrawideband antenna with two independently tunable notch bands

This paper presents a planar CPW-fed Ultrawideband (UWB) antenna with two independently tunable notch bands. The proposed design consists of a modified Rhombus-shaped monopole structure that is integrated with a dual band-stop filter based on hexagonal split ring resonators (HSRR). The antenna is capable of suppressing multiple frequency bands within ultrawideband range (3.1–11 GHz) such as WLAN and X-band downlink satellite communication frequency bands with an independent tunable mechanism to fulfill the on-demand band rejection. The frequency reconfigurability of the two notch bands is obtained by loading the hexagonal filter arms with two varactor diodes (for each band). Details of antenna design steps and reconfigurability mechanism are illustrated. The notch band element is explained using equivalent circuit model and surface current distribution at lower and higher notch frequency bands. A prototype of the proposed design is printed on the RO4003C (ϵr = 3.55) substrate printed circuit board (PCB) and tested to authenticate the performance. The proposed antenna volume is 21.5 ▪ 48 ▪ 1.524 mm3 and demonstrates an omnidirectional radiation pattern in E and H planes with an average gain of 3.7 dBi across the operational passbands, while a sharp reduction in gain of -6.8 dBi and -3.5 dBi is achieved at the lower and higher notch bands, respectively. Continuous tuning is achieved experimentally from 5.08 to 5.77 GHz and 7.75 to 8.52 GHz for the lower and higher notch bands, respectively. Excellent agreement is observed between the simulated and measured results. Application areas include radio-frequency identifications, ground-penetrating radar, and wireless communications.

Design and characteristic analysis of uniplanar multiband frequency selective surface for GSM, LTE, WLAN, ISM, WiMAX and X‐band applications

AbstractThe uniplanar compact, affordable, and unique slot‐based multiband frequency selective surface (FSS) of periodic cell size 0.14λc × 0.14λc (λc is wavelength at the initial stopband resonance) is presented in this article. The quadband FSS is analyzed using full‐wave simulation, circuit simulation (ECM), and experimental measurement where good agreement is attained. The FSS offers polarization independence with steady responses for all angular variations in the TE plane and up to 45° in the TM plane. The FSS offers dual stopbands at 2.75–4.15 and 9.45–12.48 GHz and dual passbands at 0.001–0.8 and 4.74–5.6 GHz that includes spectrum coverage of GSM, LTE, WLAN, ISM, WiMAX, and most part of X‐band communication.

Design of Dual-Stopband Rectangular Waveguide Slot Array Antennas

A dual-stopband rectangular waveguide slot array antenna is presented in this paper. Firstly, a rectangular filtering waveguide with dual stopbands is realized by periodically loading a row of T-type resonators and a row of Π-type resonators on the bottom broad wall of the rectangular waveguide, and its dual-stopband characteristic is verified by analyzing the equivalent circuit and dispersion curve. Secondly, a dual-stopband rectangular waveguide slot array antenna is obtained by etching radiation slots on the top broad wall of the filtering waveguide. To verify the proposed concept, a dual-stopband rectangular waveguide four-slot array antenna is designed, fabricated, and measured. The measured results are in good agreement with the simulation ones. The results show that, compared with the conventional waveguide slot antenna, the proposed waveguide slot antenna has almost the same radiation performance in the –10 dB impedance bandwidth of 5.51–5.95 GHz, and achieves additional suppressions of greater than 24.5 dB in 6.6–7.1 GHz and 34.6 dB in 8.4–9.3 GHz, respectively, without occupying extra space.

Highly Angularly Stable Dual-Band Stop FSS for Blocking Satellite Downlink Frequencies

High angular stability dual-band (C- and X-band) stop frequency selective surface based spatial filter is proposed in this article for blocking the satellite downlink frequencies. The unit cell of the structure consists of vertical and horizontal dipoles having two folded arms. The transmission coefficient of the filter in the designated satellite frequency bands, i.e., 3.7–4.2 GHz and 7.25–7.75 GHz has been obtained less than −10 dB. The current distribution and the equivalent circuit model of the unit cell have been illustrated to explain the resonance behavior and response of the filter. The proposed structure gives a stable response up to 85° of oblique incidence for both TE and TM polarizations. A prototype of the proposed structure has been fabricated, experimentally tested, and validated with simulation results.

C/ X‐Band sub‐harmonic mixer using single oscillator and its design flow

This article describes the concept of designing a dual-band subharmonic mixer for C-band (4.3–5.3 GHz) and X-band (9.8–11.2 GHz) applications. This mixer exploits a single local oscillator (LO) (with a frequency of 2.6GHz) with two harmonics (second and fourth), in contrast to the two LOs, utilized in a conventional dual-band mixer. This configuration results in reduced system complexity and noise. The proposed mixer utilizes two signal interference technique (SIT)-based bandstop filters at the LO port, and a dual bandstop stub at the IF port to get good isolation. A prototype of the proposed configuration is fabricated on flexible Rogers' substrate RO5880B with 0.8 mm thickness. The total implementation area of the circuit is 43 mm × 32 mm. Circuit performance is validated by measurement. Based on the measured result, the mixer performs equally well in both bands with the conversion loss (CL) in the range of 6.1–10.9 dB. The measured LO-to-IF and LO-to-RF isolations are better than 25 dB, whereas the measured RF-to-IF isolation for both bands is better than 15 dB. Further, the measured value of 1 dB compression point is found to be − 8 dBm and − 7 dBm at 5.3 and 11.2GHz, respectively.

Reconfigurable Voltage Controlled Single-Band and Multiband Bandstop Filters With High Selectivity and Wide Tuning Range

This paper presents fully reconfigurable voltage controlled single-band and multiband bandstop filters (BSFs). Distributed coupling half-wavelength resonators and multimode resonators (MMRs) loaded by varactor diodes are applied to design the proposed fully reconfigurable BSFs. A MMR is equivalent to multiple single-mode resonators and its resonant characteristics are analyzed based on the even-odd-mode method. The frequencies, bandwidths, and the number of stopbands can be independently controlled by bias voltages. The frequency and bandwidth tuning ranges can be adjusted by geometrical dimensions. Moreover, the stopband suppression level is proportional to the number of resonators. For demonstration, six pairs of half-wavelength resonators with two sets of sizes are applied to design a fully reconfigurable BSF with single, dual, triple, and quadruple stopbands. Then, three pairs of MMRs with a uniform size are applied to design a fully reconfigurable BSF with single and dual stopbands. The proposed BSFs have merits of high selectivity, wide frequency and bandwidth tuning ranges, independent controls of frequencies and bandwidths, and reconfigurable number of stopbands.

Construction of compact two‐port throne‐shaped antenna with dual stopbands and high isolation for Ultrawideband Multiple‐Input Multiple‐Output wireless communication systems

SummaryA throne‐shaped compact ultrawideband (UWB) two‐port multiple‐input multiple‐output (MIMO) antenna operating from 2.9 to 11.5 GHz is introduced. Dual‐band rejections are created at the center frequency of 5.5 and 7.5 GHz by embedding U‐slot on the feedline and split ring resonator (SRR) on the ground plane to eliminate interference with narrowband systems of these frequencies, respectively. Low mutual coupling of −22 dB is obtained almost throughout the full band by etching a rectangular slot in a cone‐shaped stub. Procedures for achieving the UWB band as well as two stopbands are discussed in detail. Current distribution, gain and radiation pattern for the proposed antenna are also studied. Peak gain of 2.51 dBi and radiation efficiency greater than 73% is obtained. Diversity parameters confirming the MIMO characteristics are also investigated. Experimental results are obtained through a practical model in the anechoic chamber to validate the simulations.

Highly-Oxidized Graphene Oxide for Achieving Low-Loss Hybrid Waveguide Gratings on SOI

In this study we fabricated highly oxidized graphene oxides (GO) to reduce the optical bulk absorption, and to achieve a low-loss GO/silicon hybrid optical waveguide. The highly oxidized GO was fabricated using triple amount of oxidants and elongated oxidizing time via a modified Hummers’ method, together with post ozone treatment to effectively break down the C = C pi-conjugation network. The high oxidation degrees of GO were confirmed by a wide interlayer spacing (1.26 nm) in XRD patterns and a high fraction of oxygenated carbon (61.57%) observed in XPS spectra. Integrating a GO thin film on top of a silicon ring resonator revealed an extra optical loss of 1.2 dB/cm, while this value reduced to 0.8 dB/cm in a GO grating covered silicon strip waveguide. The resulting GO/silicon hybrid waveguide grating provided an extinction ratio of up to 35 dB at Bragg wavelength. We further demonstrated GO/silicon hybrid waveguide moiré gratings to provide dual stopbands with a controllable stopband interval from 2.5 to 20 nm. All results validate the promising optical properties of such GO material for low-loss heterogeneous integration on silicon-on-insulator.

Compact Dual Bandstop Filter Using Folded Lines and Genetic Algorithm

A novel method for creating a dual band bandstop filter with a meandering architecture is presented. Proposed bandstop filter shows two notch bands, one at 5.6 to 7.2 GHz and the other at 8 to 11 GHz. The designed filters simulated on HFSS software and fabricated on FR-4 substrates, filter dimensions have been optimized using GA. Filter shows S11 of 1dB and S21 of -18 dB at notch frequency 6.4 GHz and S11 of 1.2dB and S21 of -38 dB at notch frequency 9 GHz. The suggested filter has two pass bands one is up to 5 GHz for wireless communication and another is from 7.4 to 7.9 GHz for C band applications.

Dual Bandstop reconfigurable (Switchable) frequency Selective surface for WLAN applications at 2.4 and 5 GHz

This work reports on an Active Meta-Surface (AMS) that is capable of switching between the two WLAN bands at 2.4 GHz and 5.0 GHz. The switching is carried out in real-time electronically with the help of PIN diodes. The unit element of the surface is built out of a vertical strip resonator with circular extensions on both edges. A section of the design is connected or disconnected from the main resonator with the help of PIN diodes to realize the switching mechanism. The design is highly miniaturized with the unit element size of 0.125 λo at the lower frequency band. Each unit element employs a pair of PIN diodes which is biased through a serial biasing mechanism thus requiring no additional DC lines along with every unit element. This simple biasing scheme adds no parasitics, hence the response with lumped components remains stable. The equivalent circuit model of the proposed design is also created for a better understanding of distributed reactances. The design achieves excellent agreement between the simulated and measured results and the angular stability of the design is intact up to 60° incident angles.

Isolation enhanced compact dual-band quad-element MIMO antenna with simple parasitic decoupling elements

In this work, a simple parasitic decoupling structure integrated compact dual-band quad-element Multiple-Input Multiple-Output (MIMO) configuration with improved isolation is proposed for 3.5 and 5.8 GHz bands of Worldwide Interoperability for Microwave Access (WiMAX) and Wireless Local Area Network (WLAN) applications. The lower and higher frequency bands accomplish an impedance bandwidth of 400 MHz (3.35 – 3.75 GHz) and 450 MHz (5.6 – 6.05 GHz), respectively. A slot integrated curve-shaped compact (11 × 20 mm2) dual-band monopole antenna is explored to implement the proposed compact MIMO configuration. A parasitic decoupling structure comprising T and inverted L-shaped thin metal strips is introduced between the orthogonally placed antenna elements. It exhibits dual stopband characteristics to enhance the isolation significantly at the targeted frequency bands despite the compact footprint (34 × 34 mm2) of the MIMO geometry.The optimized decoupling structure improves the isolation between the elements by 31.5 and 32 dB in the lower and higher bands than the MIMO geometry without decoupling elements. The antenna provides good radiation characteristics with peak gains of 4.18 and 3.62 dBi within the bands. The computed diversity metrics, such as envelope correlation coefficient (< 0.01), diversity gain (> 9.93 dB), mean effective gain ratio (-0.13 to 0.16 dB), channel capacity loss (< 0.4 b/s/Hz), and total active reflection coefficient (< -10 dB), ensures good diversity performance. The fair agreement between the simulated results using HFSS EM solver and the measured results on the fabricated prototype validated the proposed MIMO configuration.

Miniaturized dual stop band frequency selective surface with broadband linear co to cross polarization conversion ability

This work presents a miniaturized angularly stable frequency selective surface (FSS) on a single layer substrate. Unit cell comprises of convoluted circular rings connected cross dipole and linear arrow headed dipole printed on both sides of the substrate. A closely spaced dual stop band resonances are obtained at 10 and 14.3 GHz with frequency ratio of 1.43. FSS shows a − 10 dB stopband bandwidth (BW) from 7.32 to 11.05 GHz (40.61%) and 12.68 to 15.97 GHz (22.97%) with >30 dB stop band rejection at center frequencies. FSS poses the features of stable performance under change in polarization and angularly stable response up to 60° incident angle. Later the proposed FSS is printed on grounded thick dielectric substrate and it shows broadband reflection type co to cross polarization conversion from 7.2 to 17.32 GHz (82.54%) with polarization conversion ratio >80% and oblique angle stability up to 35°. To the best of authors' knowledge, this is the first time in literature a single unit cell geometry with two different properties, spatial filtering on transmission and polarization conversion on reflection have been designed and analyzed in details. A finite array with size 25 × 25 of the proposed FSS is fabricated and the measured filter response shows a good agreement with simulated performance at normal and oblique incidences. The proposed FSS is used as a reflector of a dual band monopole antenna and the simulation results shows gain improvement of 5.51 and 3.8 dB at the two stopband frequencies.

A Dual stopband two-sided frequency selective surface for mobile shielding applications

A two-sided frequency selective surface (FSS) is proposed to shield two bands of the mobile frequencies (EGSM-900 and DCS-1800). The FSS consists of an array of square concentric-rings cells printed on both sides of the substrate to offer better shielding of the two mobile frequencies. The CST Microwave suit is used for the simulations. The equivalent circuit model for the two-sided FSS is analysed and the transmission frequency in terms of the two stop frequencies is estimated. The obtained shielding is better than 40 dB across the two bands. The proposed FSS can be used to reduce mobile radiation or to isolate halls from nearby mobile base stations. The bandwidth of the FSS cell can be increased by using ring pairs of unequal sizes on the two sides of the substrate.

Coupled microstrip slot resonators for bandstop filters: theory and design

Bandstop filters with single and dual stop-bands were implemented using coupled mode microstrip slot resonators (MSRs) for the first time. With compact and ease of fabrication, the MSRs provide excellent filter response as desired. It is found that the MSRs can offer narrow bandwidth of less than 20% fractional bandwidth and large isolation of more than 40 dB. The designs of MSRs and filters are systematically demonstrated with the method of coupled mode resonator theory. MSRs may be potential alternative for complicated and arbitrary design of BSFs to achieve desired frequency response.