Wide Stopband Research Articles

Analytical modeling and 3D printing of locally resonant composite sandwich metamaterials with inertial amplification mechanisms

In this paper, a locally resonant sandwich metamaterial beam with inertial amplification mechanisms is presented for flexural vibration attenuation. This sandwich metamaterial is proposed as a lightweight structure with a low-frequency stopband. An analytical model was developed to derive the equations of motion for the resonator core and skin plate using Hamilton’s principle. Analytical solutions for the stopband boundary frequencies were derived from the equations of motion. The analytical solutions demonstrated that inertial amplification resonators can exhibit lower resonance frequencies than linear spring-mass resonators with the same weight and spring constant. It was also shown that the proposed sandwich beam exhibited a lower frequency stopband in exchange for the stopband width. Finite element method analyses and experiments were performed to investigate the frequency response of the sandwich beam. The flexural vibration of the sandwich beam was significantly attenuated within a certain frequency range. The frequency range with low transmissibility agreed well with the stopband predicted by the analytical solutions.

Design and analysis of a tunable electromagnetic lever-type anti-resonant vibration isolator

To broaden the effective vibration suppression band of a typical dynamic anti-resonant vibration isolator (DAVI), a tunable lever-type anti-resonant vibration isolator has been designed, theoretically investigated, and experimentally verified. An anti-resonant frequency occurs within the device when the inertial force generated by the levered mass cancels the spring force. By controlling the electromagnetic spring so as to adjust the system’s equivalent stiffness, the anti-resonant frequency of the electromagnetic lever-type anti-resonant vibration isolator (EM-LVI) can be tuned to coincide with the excitation frequency in real time. A broad stopband where the vibration is sufficiently suppressed can be provided by the EM-LVI for low-frequency applications. Due to the lever’s amplifying effect, the EM-LVI can modify the equivalent stiffness of the system with a small electromagnetic stiffness, which provides a viable approach to the design of lightweight isolators. Theoretical and experimental results demonstrate that the tuning bandwidth increases along with the lever amplification ratio. With the advantages of a wide stopband and a high vibration suppression level, the proposed EM-LVI exhibits significant advantages in suppressing low-frequency vibration in a finite-frequency band and has been successfully validated by experimental prototypes for its beneficial performance in low-frequency vibration suppression.

Novel Meandered Line EBG Filters with Significant Size Reduction Using Sine Tapering

Tapering electromagnetic bandgap (EBG) structures is a common method in designing microstrip filters with different periodic structures. A novel technique for tapering EBG structures with the amplitude coefficients obtained from the sine function has been illustrated. This method deduces mellifluous coefficients that improves the performance with reasonable stopband width, preferable insertion loss level, and much-minimized passband ripples compared to similar designs with other tapering methods (e.g., binomial distribution, Chebyshev distribution, and conventional cosine tapering). It also offers tandem use of tapered EBG structures, leading to the novel meandered transmission line tandem design that significantly reduces the length of the filter; more than 40% is possible, compared to the uniform and conventional tapered designs. Size reduction on such a large scale will benefit the designers with the limited space issues.

Design of substrate integrated-waveguide wide stopband bandpass filter for 5G applications

Design of substrate integrated-waveguide wide stopband bandpass filter for 5G applications

A Low-Profile Dielectric Resonator Filter with Wide Stopband for High Integration on PCB.

A low-profile dielectric resonator (DR) filter is proposed to achieve the feature of high integration and wide stopband. The high integration is due to the structure of printed circuit board (PCB) substrate instead of metal cavity, which can be easily integrated with other planar circuits. Thus, the proposed design can improve the integration level and reduce installation errors. Moreover, the out-of-band harmonics can be well suppressed by the structure combined with introducing rectangular hollowing in the center of the dielectric block, coupling the feed and loading 1/4λ wavelength branch. For demonstration, it is fabricated and measured. The simulated and experimental results with good agreement are presented, the insertion loss is as low as 1.1 dB, the profile height is only 0.77λg, and the stopband reaches 2.61f0.

Wide stopband QMSIW diplexer with large frequency ratio and flexible specification

AbstractIn this letter, a wide stopband quarter‐mode substrate‐integrated waveguide (QMSIW) diplexer is proposed. By using coupling feeding lines and QMSIW cavities, the two passbands of the diplexer can be controlled independently by their respective QMSIW bandpass filters. In comparison to other counterparts, the proposed diplexer provides flexible passband specification, compact size, and high isolation. The design exhibits a wide 20‐dB stopband up to 3.2f0, a frequency ratio of 1.6, and a high isolation level larger than 42.2 dB across the passbands.

Compact hybrid eighth‐mode substrate integrated waveguide and microstrip line filters with mixed electric and magnetic coupling

AbstractThis paper proposes a new type of hybrid eighth‐mode substrate integrated waveguide (EMSIW) and microstrip line (MSL) bandpass filter (BPF) with mixed electric and magnetic coupling. Firstly, two second‐order EMSIW BPFs with mixed coupling and wide stopband performance are investigated. Then, in order to realise high‐order BPF with decent performance, half‐wavelength (λ/2) open‐circuited MSL resonators are employed in the hybrid BPFs design. In the end, two third‐order BPFs and a fourth‐order BPF are developed by combining the EMSIW and MSL resonators together. Extra transmission zeros can be introduced due to the cross couplings in the trisection and quadruplet topologies. For demonstration, the proposed prototypes are designed, fabricated and measured. Reasonable agreements can be achieved between the measurement and simulation. The proposed third‐order BPFs compete against the state of the art, exhibiting the competitive characteristics of the operating bandwidth, physical footprint and upper‐stopband rejection with less order. The proposed fourth‐order BPF features a compact size of 0.34 × 0.34λ0, a low insertion loss of 1 dB, a broad 3‐dB fractional bandwidth of 22.9% and an excellent lower‐stopband suppression.

A Common-Resonator Filtering Hybrid With a Wide Stopband and Compact Size

A Common-Resonator Filtering Hybrid With a Wide Stopband and Compact Size

Design of superconducting ultra‐wideband filter with wide stopband based on quintuple‐mode resonator

AbstractIn this paper, a new ultra‐wideband (UWB) bandpass filter (BPF) based on QMR (quintuple‐mode resonator) loaded with quasi‐lumped elements is proposed for wide stopband application. The method of connecting five folded U‐shaped resonators with rectangular patches to construct a QMR was proposed. By adjusting the relative position of the rectangular patches, the frequency band width of the filter can be freely adjusted. Further, quasi‐lumped elements were loaded to the QMR to generate three transmission zeros to enhance stopband performance. The filter designed in this paper can independently adjust both the stopband and the passband, providing greater design flexibility. The passband of the final filter is 3.18–9.43 GHz, and the FBW (fractional relative bandwidth) is 99%. The out‐of‐band rejection is better than −15 dB in the frequency range of 9.6–28.42 GHz. The measurement results show good performance without any tuning, and are in good agreement with the simulation results.

Highly‐selective microstrip bandpass filters based on new dual‐mode fan‐shape patch resonators

AbstractA design method for highly‐selective bandpass filters based on novel dual‐mode fan‐shaped patch resonator (FSPR) is presented in this article. Different from traditional dual‐mode patch filters, two higher‐order modes TM020 and TM110 are utilised to generate a passband, and the two resonant frequencies can be controlled well by its radius and angle. A dual‐mode filter with two transmission zeros (TZs) is implemented by using one FSPR, and locations of TZs can be controlled well. To further improve the selectivity of FSPR filters, four‐pole filters based on two identical dual‐mode FSPRs with co‐directional and reverse‐directional cascade are simulated, fabricated and measured. Furthermore, three‐ and four‐pole filters based on dual‐mode FSPR and single‐mode uniform impedance resonators are proposed, which are also simulated, fabricated, and measured. The later proposed filters not only achieve high selectivity and wide stopband, but also have simple structure and small size.

High-Roll-Off-Rate Ultrathin Polarization-Rotating Frequency Selective Surface

This letter introduces a transmission FSS with excellent roll-off feature, ultra-thin thickness, low insertion loss and wide rejection bands. Three novel basic component structures are developed based on the polarization rotator (PR) structure leading to multi-transmission zeros and poles which can be independently controlled. Theoretical analyses and simulations are carried out, and a prototype is fabricated and measured. The proposed FSS exhibits double sharp roll-off sidebands, ultra-thin thickness and low insertion loss, as well as two wide stopbands. In addition, the proposed FSS shows stable responses with oblique incidence up to 45 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^\circ$</tex-math></inline-formula> . As a result, the tight agreement between measurement and simulation validates the design principle.

Compact and Wide Stopband Bandpass Filters Based on Dual-Mode Folded Circular Substrate Integrated Waveguide Cavities

This article presents a novel class of compact and wide stopband bandpass filters based on dual-mode folded circular substrate integrated waveguide cavities (FCSIWCs). By employing both TM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{020}$</tex-math> </inline-formula> and TM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{110}$</tex-math> </inline-formula> modes of the FCSIWC as resonant modes and TM <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{010}$</tex-math> </inline-formula> mode as nonresonating mode, a doublet with two poles and two transmission zeros (TZs) is implemented. The TZs can be located either both below or both above the passband, or one below and one above. By combining the dual-mode FCSIWC and single-mode folded rectangular substrate integrated waveguide cavities (FRSIWCs), a class of compact and wide stopband four-pole box-section filters is proposed. In addition, a more selective five-pole extended box-section filter is implemented by loading a complementary split-ring resonator (CSRR) on the four-pole filter structure, without occupying any additional area. Two prototypes are fabricated and measured to validate the proposed filters.

A new design of ultra-thin wide stop-band metamaterial filter for terahertz waves

A new design of ultra-thin wide stop-band metamaterial filter for terahertz waves

Dual‐band filtering power amplifier with extended passband bandwidths and wide stopband rejection

AbstractThis article presents a dual‐band filtering power amplifier (DB‐FPA) with extended passband bandwidths and wide stopband rejection, which is helpful in reducing the number of microwave components in the dual‐band radio frequency front end, resulting in compact circuit size and low loss. In the designed DB‐FPA, a wideband low‐pass filter is applied as the input matching network (IMN) to provide wideband impedance matching and good stopband rejection, while a dual‐band filtering impedance transformation is adopted as the output matching network (OMN) to provide dual‐band impedance matchings and filtering responses simultaneously. Specifically, the IMN is constructed by high‐impedance transmission‐line sections and low‐impedance open‐circuit stubs. The OMN is designed based on the specific external quality factors and coupling coefficients during two bands, resulting in dual‐band impedance transformations and dual‐band filtering responses. Then, based on the above IMN and OMN, the design procedure of the presented DB‐FPA is summarised. To verify the proposed idea, a novel DB‐FPA has been fabricated and measured. During the two frequency bands, the measured maximum power added efficiencies are 55.11% and 47.78% within 33.0 dBm input power, while the measured peak gains are 15.4 and 14.0 dB within 15.0 dBm input power.

Broad Stopband, Low-Loss, and Ultra-Compact Dual-Mode Bandpass Filter Based on HMSIRC

In this investigation, an ultra-compact dual-mode bandpass filter (BPF) with a wide stopband response is realized by using a half-mode substrate-integrated rectangular cavity (HMSIRC). The HMSIRC resonator is designed with a cavity that is rectangular in shape and has metallic vias along three of the sides. The fourth side is open-ended and contains microstrip feed lines. For the purpose of constructing a magnetic wall, a rectangular slot is cut into each of the HMSIRC’s three edges. In order to produce an electrical wall that may generate a variety of resonances, the side with the open edges is provided with a single metallic via in the center. After that, a second-order BPF is generated by loading a transverse slot in the middle of the BPF, which enables independent frequency regulation of the mode frequencies. The eigen-mode analysis; field distributions; coupling matrix; and full-wave simulation of the proposed HMSIRC filter topology are used to develop the working principle of the filter. A second-order BPF is realized, constructed, and experimentally validated in order to provide evidence that the theory is correct. The BPF prototype achieves satisfactory performance thanks to its compact footprint of 0.028 λg2; its broad passband of 15.9%; its low insertion loss of 0.41 dB; and its wide stopband of 4.36 f0 with a rejection level greater than 20 dB. Both the measured and EM-simulated responses of the BPF are very consistent with one another.

A UWB bandpass filter based on elliptical open stub-loaded resonator and dumbbell-sided cross-circle DGS

An Ultra-wideband (UWB) bandpass filter (BPF) based on an elliptical open stub-loaded resonator (EOSLR) and dumbbell-sided cross-circle (DSCC) defected ground structure (DGS) is proposed in this paper. The measured results show that the 3 dB bandwidth of the filter is 3.49 ∼ 11.04 GHz, the skirt factor (S.F) is 0.844, the upper stopband rejection is greater than 20 d B at 11.70 ∼ 26.80 GHz, and the stopband width is 15.1 GHz. The proposed filter has the advantages of high selectivity and extremely broad upper stopband and it can be applied in UWB Wireless communication system.

Wideband Filtering Rat-Race Coupler with Shared Triple-Mode Resonator

In this paper, a filtering rat-race coupler (FRC) is presented, which features the merits of a wideband filtering response, good impedance matching at both input and output ports, good isolation, high-frequency selectivity, small in-band phase difference error, a wide stopband, and small size. It was composed of two leading triple-mode resonators, one core section, and two λ/2 open-circuited transmission lines (TLs). The core section consisted of three λ/4 TLs and one λ/4 short-circuited parallel coupled line (CL). The leading triple-mode resonator consisted of one λ/4 short-circuited stub and two λ/4 TLs. By loading the triple-mode resonator as the shared component and combining it with the core section, a wideband filtering response with four transmission poles could be achieved. In addition, two transmission zeros were generated by loading the λ/2 open-circuited TLs to the output ports of the FRC. The working principles of the proposed FRC are analyzed, and equations are derived with parametric analysis. For demonstration, a prototype operating at the center frequency of 1.4 GHz was designed, fabricated, and measured. Measurement results show that a fractional bandwidth of more than 60% was achieved under the criteria of 10 dB return loss and 20 dB isolation. In this bandwidth, the amplitude imbalances and phase difference errors were less than 1 dB and 10°, respectively. Additionally, it also exhibited high selectivity and a wide stopband.

A wideband bandpass filter with wide upper stopband attenuation containing multiple resonators

AbstractA compact wideband bandpass filter with a wide passband and very‐wide out‐of‐band suppression is presented. The filter is constructed from a central rectangular‐ring resonator with two open stubs placed around it symmetrically. In addition, tri‐section stepped‐impedance resonators are symmetrically distributed on both sides of the two open stubs, and two symmetrical funnel‐shaped resonators are included to enhance out‐of‐band suppression. The out‐of‐band performance of filter is very good, with a suppression level greater than 20 dB up to 25.72 GHz. The center frequency of the filter is 5.84 GHz, with a fractional bandwidth of 115.8%. Good agreement between the simulations and measurements validates the design principle.

High-Order Quasi-Elliptic-Type Wideband Bandpass Filter With Ultrabroad Input-Reflectionless Stopband Range

A two-layer wideband bandpass filter (BPF) with ultrabroad input-reflectionless stopband range is reported. It consists of a two-port-reflectionless high-order quasi-elliptic-type (QET) wideband BPF and two similar input-reflectionless low-pass filter (LPF) stages. The constituent 2-GHz BPF is shaped by two vertical transitions with shunt resistively terminated T-junctions, which are connected through a microstrip T-junction. It features a two-port-absorptive ninth-order in-band quasi-equiripple BPF response with two close-to-passband transmission zeros (TZs). The building LPF is made up of two in-series-cascaded input-reflectionless LPF units with their first TZs at 6 and 12 GHz, which results in an extended upper stopband beyond 18 GHz. Through this LPF-BPF-LPF approach, an extremely wide input-reflectionless stopband range with increased power attenuation levels in the overall BPF is attained. Its theoretical RF operational principles are detailed. Furthermore, for experimental validation purposes, a two-layer microstrip wideband BPF prototype is simulated, manufactured, and measured. It exhibits a minimum stopband power attenuation level of 29.57 dB, along with minimum input-power-matching levels of 10 and 6.7 dB from dc to 9.85 GHz and from dc to 20 GHz, respectively.

Wideband Low-Loss Filter With Compact Size and Wide Stopband Based on Folded Planar Waveguide

In this letter, a hybrid, compact doubly slot-loaded folded ridged half-mode substrate-integrated waveguide (FRHMSIW) filter with wide bandwidth and high selectivity is presented and investigated. The low-pass and high-pass cutoff frequencies of the wideband filter can be independently controlled by adjusting the dimensions of the quasi-periodic slots and FRHMSIW sections, respectively. The dispersion curves, surface current distribution, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E$</tex-math> </inline-formula> -field vector diagram of the proposed hybrid FRHMSIW bandpass unit are illustrated. Parametric study and loss analysis are also conducted. The footprint of the proposed filter is miniaturized due to the upper-side-slot-loaded FRHSIW transmission structure and meandered middle-layer slots. The stopband is further extended by etching I-shaped patterns on the ground layer. Finally, the filter is designed, simulated, and measured, with a wide passband between 3.86 and 8.3 GHz, a minimum insertion loss of 0.56 dB, a rejection level better than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$-$</tex-math> </inline-formula> 20 dB from 8.6 to 20.8 GHz, and an electrical size of only 0.21 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\lambda _{g}^{2}$</tex-math> </inline-formula> at the center frequency.