Wide Stopband Research Articles

Compact Bandpass Waveguide Filters with Inductive Couplings with E-plane Symmetry and without E-plane Symmetry

Introduction. Modern satellite communication systems continue to impose stricter requirements on the frequency response, weight, and size of filters. In this paper, several designs of bandpass filters with inductive couplings on corrugated waveguides are considered. Although such filters have been described previously, this paper considers their possible implementations based on narrow cross-section waveguides, as well as on structures with and without electric field symmetry.Aim. To study filters with inductive couplings with and without electric field symmetry, as well as to assess the filter stopband width and attenuation.Materials and methods. Numerical studies were carried out by the finite element method (FEM) and the method of final difference in the time domain (FDTD).Results. Modeling of filters with inductive couplings with and without electric field symmetry was carried out. Filters without electric field symmetry were found to exhibit higher characteristics in terms of weight and size, at the same time as having a narrower stopband. The conducted modeling also showed that filters with stubs of the same cross section allow stopband attenuation to be improved by almost 20 dB compared to filters with stubs of varied cross section. The frequency responses of filters with inductive couplings obtained by electrodynamic modeling were established to agree well with those obtained experimentally. A ten-order ultra-compact filter with inductive couplings without electric field symmetry was considered, with the bandwidth loss of not more than 0.7 dB, the attenuation of at least 80 dB in the frequency range from 7.9 to 8.4 GHz, and the filter length of 30 mm.Conclusion. The use of filters with inductive couplings allows their mass and dimension characteristics to be significantly improved without increasing losses in the bandwidth at the same time as maintaining a high level of attenuation in the stopband.

Design of Hybrid Fractal Integrated Half Mode SIW Band Pass Filter with CSRR and Minkowski Defected Ground Structure for Sub-6 GHz 5G Applications

A compact and wide-stop band half mode substrate integrated waveguide (HMSIW) filter, incorporated with a hybrid fractal on the upper plane and a complementary split ring resonator (CSRR), along with a defected ground structure (DGS) etched on the bottom plane, is proposed for 5G sub-6 GHz application. A CSRR reduces the resonant frequency causing size miniaturisation by approximately 40% by augmenting the equivalent inductance and capacitance of the CSRR. Further, the low-pass characteristics of the DGS aid in suppressing out-of-band spurious harmonics. A two-pole band pass filter (BPF) is fabricated using FR4 (flame retardant) to validate the design. The results confirm that the proposed filter has a pass band from 3.75 GHz–5.12 GHz with spurious response below −20 dB > 4f0.

Ultra-compact and broadband all-silicon TM-pass power splitter using subwavelength holey-structured metamaterial waveguides.

Power splitters with polarization management features are highly desired to construct high-density silicon photonic integrated circuits. However, few attempts have been made to design a single device that can act as both a power splitter and a TE- or TM-pass polarizer. In this paper, for the first time, we experimentally demonstrate an ultra-compact and broadband all-silicon TM-pass power splitter, where a triple-guide directional coupler (TGDC) composed of three parallel subwavelength holey-structured metamaterial waveguides (SHMWs) is located at central coupling region and three regular strip waveguides are connected at the input/output ports. Such a SHMW can enhance the reflection to realize a wide stop-band for the undesired TE polarized light, while achieving the low loss transmission for the TM polarized light. Besides, the TM dispersion can be significantly flattened by the designed SHMWs, leading to a broadband power splitting for TM polarization. Simulated results show that an ultra-compact device of 1.7 × 4 µm2 in size is obtained with an insertion loss (IL) of 0.34 dB and an extinction ratio (ER) of 36 dB at 1550 nm, and its working bandwidth can be extended to ∼240 nm by keeping IL < 0.9 dB and ER > 16 dB. The measurements of the fabricated devices show low IL (<1 dB) and high ER (>15 dB) over the measured wavelength range of 1460 to 1580 nm, which is consistent with the simulation results.

Band-stop characteristics of a nonlinear anti-resonant vibration isolator for low-frequency applications

In order to broaden the vibration attenuation bandwidth of passive isolation systems in low-frequency applications, a nonlinear anti-resonant vibration isolator was studied by coupling a lever-type vibration isolator with a nonlinear vibration absorber. By appropriately designing the structural parameters, a wider double-attenuation stop-band emerges from the coupling of the levered mass and the absorber mass. Theoretical results show that the bandwidth of the proposed NL-AVI is much wider than that of an existing lever-type vibration isolator. A parametric influence investigation shows that the transmissibility and width of the stop band can be flexibly designed with structural parameters. The cubic nonlinearity of the vibration absorber has the effect of shifting the anti-resonant frequency and the resonant peak to higher frequencies, thereby increasing the stop band width. The proposed nonlinear anti-resonant vibration isolator provides a distinctive mechanical mechanism for realizing a combination of band transmissibility and width in the vibration attenuation characteristics and has been successfully validated by experimental prototypes for their advantageous performance in low-frequency vibration isolation.

Attenuation‐tunable balanced bandpass filter based on graphene nanoplates

In this letter, a unique type of balanced bandpass filter (BPF) with high selectivity and tunable attenuation is proposed through the comprehensive design of a microstrip balanced BPF and graphene nanoplates. In order to achieve the passband response in differential-mode (DM) excitation and produce a wide and deep stopband in common-mode (CM) excitation, the balanced couple of lines are used in balanced BPF. The graphene nanoplates are loaded on the open ends of λ/4 stepped-impedance resonators to dissipate the electromagnetic field. By raising the bias voltage applied to the graphene nanoplates, the values of the graphene's surface impedance can be adjusted from high to low. The insertion loss of the balanced BPF can be indirectly tuned while maintaining the return loss at a comparatively low level. A prototype of the proposed gain tunable balanced BPF is fabricated and measured. The measured results show that a tuning range of insertion loss from 1.75 to 10.7 dB can be obtained for the DM circuit over the operating bandwidth centered at 1.84 GHz, without interrupting the signal rejection of the CM circuit.

A micromachined ultra‐wide stopband lowpass filter based on stepped impedance resonator loaded T‐shaped structure

This article presents an additively manufactured micro-coaxial lowpass filter with ultra-wide stopband suppression. To achieve a wide stopband response, two-stage stepped impedance resonator loaded T-shaped structures are used to substitute the low impedance transmission lines in the lowpass filter prototype to generate extra transmission zeros in the stopband. Shunt open-ended stubs are introduced to the structure in flexible positions to further strengthen the suppression at specific frequency points. The filter is designed with 22 GHz passband and the 20 dB stopband suppression bandwidth over 300 GHz. The micro-coaxial lowpass filter structure was fabricated based on additive metal micro-manufacturing process with the rectangular cross-section dimensions of 0.5 mm × 0.5 mm (300 GHz cutoff frequency). To facilitate the measurement, pair of coax-to-CPW transitions are added at the input/output ports. The measurement results show excellent agreement from DC-110 GHz (limitation of the measurement device), with insertion loss of 1.05 dB at the cutoff frequency fc, which validates the design.

New Method for the Microstrip Bandstop Filter With a Wide Stopband and an Extremely High Attenuation

A new method for the design of microstrip bandstop filter with a wide stopband and an extremely high attenuation is proposed. At the input and output ports of this bandstop filter, the tight coupling has been adopted for the coupled line with a single-ended ground. Then, a wide bandwidth and a steep slope will appear at the edge of the stopband. Moreover, two coupled bandstop-mode resonators added can result in an extremely high attenuation within the stopband. Two structures are then cascade connected. Eventually, this bandstop filter, with the attenuation of 56 dB and a fractional bandwidth of 68.4%, is developed.

Multilayer Substrate Integrated Waveguide Filter With Multimode Suppression and Wide Stopband

This brief presents a new wide stopband substrate integrated waveguide (SIW) filter with multimode suppression based on a multilayer structure. All spurious modes below TE404 of a multilayer SIW filter operating in TE101 could be effectively suppressed by moving the intercoupling slots away from the sidewall by about 1/6 of the cavity’s width. To verify it, two prototypes are designed, fabricated, and measured. The results show a small size and a wide stopband of up to 4.03 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f} _{0}$ </tex-math></inline-formula> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f} _{0}$ </tex-math></inline-formula> is the filter’s center frequency) with a simple design. The proposed technology could be efficient for developing wide stopband SIW filters in wireless/microwave circuits and systems.

Compact 1.75–2.7 GHz Tunable BPF With Wide Stopband Up to 9.5 GHz Using Harmonic-Controlled SIDGS Resonators

In this brief, a harmonic-controlled substrate-integrated defected ground structure (SIDGS) resonator with tuning capacitor is proposed for the design of tunable filter. Such resonator exhibits a harmonic-controlled characteristic. The fundamental resonant frequency can be properly tuned, while the spurious resonance is controlled at much higher frequency to achieve a wide stopband. To verify the principle, a tunable bandpass filter (BPF) is designed and fabricated based on the resonator. The center frequency can be tuned from 1.75 to 2.7 GHz. Meanwhile, the stopband can extend up to 9.5 GHz with a rejection level of 20 dB for all tuning cases. The BPF also exhibits low insertion loss (i.e., 1.1–1.9 dB) and compact size (i.e., 0.07 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\lambda _{g}}\,\,{\times }\,\,0.08\,\,{\lambda _{g}}$ </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">${\lambda _{g}}$ </tex-math></inline-formula> is the microstrip guided wavelength at the 1.75 GHz).

Compact Triple-Mode Folded-HMSIW Diplexer With Wide Stopband and High Isolation Based on Embedded Isolation Network

In this brief, a triple-mode folded half mode substrate integrated waveguide (HMSIW) diplexer with wide stopband and high isolation based on embedded isolation network is proposed. The embedded isolation network of SIW diplexer is introduced to achieve miniaturization, low insertion loss and flexible design of high isolation between two channels for the first time. Triple-mode folded HMSIWs with loading different slots are utilized to design filtering responses in two channels, which can further reduce size and insertion loss of the diplexer. Besides, the wide stopband can be obtained for feeding technology in Channel 1 and harmonic mutual suppression technique in Channel 2. In final, a prototype with 3-dB fractional bandwidths of 14.6% (Channel 1) and 6.2% (Channel 2) is designed and fabricated at 5.05 GHz (Channel 1 @ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{1}$ </tex-math></inline-formula> ) and 7.46 GHz (Channel 2 @ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{2}$ </tex-math></inline-formula> ). The in-band isolations and upper-stopband attenuation are better than 55 dB / 49 dB (Channel 1 / Channel 2) and 20 dB extended to 12.3 GHz ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2.43f_{1}$ </tex-math></inline-formula> ). It occupies only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.56~{\lambda }_{\mathrm{ g}}^{2}$ </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">${\lambda }_{\mathrm{ g}}$ </tex-math></inline-formula> is the guided wavelength at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$f_{1}$ </tex-math></inline-formula> .

Design of Wideband Filtering Quadrature Coupler Consisting of Inductor-Loaded Coupled Line With Three-Coupled-Lines

In this brief, the design of a wideband filtering quadrature coupler is presented. It is composed of an inductor-loaded coupled line (I-CL), two open-ended stubs, four short-ended stepped impedance resonators, and four three- coupled-lines (TCLs). Wideband operation with three resonant points is generated by using the I-CL with the TCLs. Due to the utilization of short-ended resonators combined with the open stubs, wide stopband is also obtained. Design formulas are derived using the even-odd decomposition technique and optimization process is given for guidance. For demonstration, a 3-dB prototype is designed, fabricated and measured. Measurement results show that a bandpass bandwidth (BPBW) of 43% is realized under the criterions of 15-dB return loss and isolation. While the BPBWs for 0.5-dB amplitude imbalance and 5° phase difference fluctuation are 40.3% and 48%, respectively. Besides, wide stopband extends to 2.64 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f} _{0}$ </tex-math></inline-formula> is realized with more than 10 dB rejection level.

SIW Bandpass Filter With Wide Stopband Using Harmonic Interleaving and Orthogonal Transmission Techniques

In this article, a wide stopband substrate integrated waveguide (SIW) bandpass filter (BPF) centered at 36.48 GHz with a 3-dB fabrication bandwidth (FBW) of 1.78% is presented and developed based on the orthogonal transmission techniques. Fourth-order Chebyshev filtering response with two transmission zeros (TZs) located at 35 and 41 GHz can be obtained by the exploitation of alternating electromagnetic (EM) coupling topology including negative excitation and planar coupling structure. Combining with the harmonic interleaving between resonant cavities with slot lines etched on the ground plane, the simulated out-of-band suppression is better than 20 dB with frequencies up to more than <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$8f_{0}$ </tex-math></inline-formula> , and the measured stopband is extended to 110 GHz due to the limitation of test condition. Good agreements between simulations and measurements can be observed.

Wideband and miniaturized lumped‐element low temperature co‐fired ceramic filter Using size reduced resonators for very high frequency applications

A wideband and miniaturized bandpass filter (BPF) is proposed using size reduced resonator (SRR) for the very high frequency band applications. The proposed SRR places vertically interdigital-capacitor inside spiral inductor, thus two L-C elements only take up one inductor's area. Therefore, significant size reduction and integration increment are both achieved without increasing the number of substrate layers. The BPF is built on a 10-layer thickness low temperature cofired ceramic substrate and has the smallest reported size of only 0.00 7 λg × 0.004 λg × 0.0005 λg. Moreover, the BPF also achieved a wide fractional bandwidth of 97.2%, a low in-band insertion loss of only 0.7 dB, a great selectivity BW20 dB/BW3 dB of 1.23 and a wide stopband up to 2.2f0 with 20 dB suppression. Furthermore, comparisons and discussions are also implemented.

Compact filtering balun based on coupled‐line‐loaded hairpin ring resonators with extended stopband

A filtering balun with compact size and extended stopband is designed in this paper. This design is based on a novel coupled-line loaded hairpin ring resonator (C-HRR). First, the odd- and even-mode transmission characteristics of the C-HRR are carefully analyzed. Then, the miniaturization and large-frequency-ratio features of the C-HRR are discussed and summarized. The out-of-phase current distribution at the odd-mode resonant frequency is noticed. Finally, to validate the features of the C-HRR, a filtering balun with wide upper stopband is designed, fabricated, and measured. Measured results show that the filtering balun can operate at 2.46 GHz with 0.5 dB magnitude imbalance and 4° phase imbalance. The circuit size of the filtering balun is only 0.24λg × 0.068λg, where λg is the guide wavelength at the center frequency fc. A wide stopband with 19.3 dB rejection from 1.05fc to 3.25fc is obtained. Both simulated and experimental results are in good agreement with each other.

A Fully Packaged Bandpass Filter on Stripline Patch Resonator With Wide Upper Stopband

In this letter, a fully packaged dual-mode bandpass filter (BPF) with wide upper stopband is presented. The stripline patch resonator loaded by the shorting slabs is adopted to achieve the dual-mode bandpass performance under operation of TM00 mode and TM01 mode. To remove other harmonic resonances of the stripline patch resonator, a common-mode double-point inset-feeding technique is proposed at the very beginning to prevent the excitation of high-order modes. To verify the design concept, a prototype packaged dual-mode BPF working at 4.0 GHz with the fractional bandwidth (FBW) of 8.2% is designed and fabricated using the multilayer liquid crystal polymer (LCP) circuit technology. Final results theoretically demonstrate and experimentally confirm that a wide stopband rejection up to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4.3f_{0}$ </tex-math></inline-formula> is obtained, well verifying the feeding method.

Sharp roll‐off triband microstrip bandpass filter with wide stopband for multiband wireless communication systems

Design of a novel triband bandpass filter is presented for wireless communications systems. The filter is based on inter-coupled stepped impedance resonators and inter-digitally coupled to the input/output ports. The configuration of the filter circuit consists of open-loop resonators that are electromagnetically coupled to each other using inverted T-shaped open stubs. The intrinsic characteristics of filter structure generates five transmission zeros that results in triband bandpass response exhibiting sharp selectivity, high inter-band isolation and a wide out of band rejection. Unlike other triband filters reported recently in literature the proposed single layer filter does not require any short-circuited plated through hole which can introduce fabrication complexity and therefore production costs. Moreover, the triband structure can be configured to provide passbands with identical 3-dB fractional bandwidth and whose center frequency can be equally spaced. In the proposed prototype design presented here the passband frequencies are set to 3.6, 4.6, and 5.6 GHz that corresponds to WiMAX, 5G, and WLAN applications. The consequence of employing open-circuited transmission lines in the design results in a relatively large structure, which can be overcome by employing higher dielectric constant substrate. The proposed triband filter was designed to achieve identical 3-dB fractional bandwidth of 11.9%. Measured results confirm inter-band isolation better than 30-dB. The theoretical model is consistent with the measured results.

Design of a Filtering Power Divider with Simple Symmetric Structure Using Stubs

A power divider (PD) with a wide stopband and simple symmetric structure using open- and short-ended stubs is analyzed and implemented in this paper. In the proposed power divider, for the first time, the output resistor is divided into two sections and open- and short-ended stubs are used between the resistors. The incorporated open- and short-ended stubs have resulted in a controllable bandwidth for the proposed PD, which resulted in 40% of the fractional bandwidth considering 3 dB attenuation of insertion loss. The proposed PD operates at 2 GHz, which shows more than 20 dB attenuation for the return and isolation losses. In addition, the obtained insertion loss at the operating frequency is approximately 0.3 dB, which shows a minor loss, and also, high isolation is achieved in the device. Moreover, 20 dB and 30 dB attenuation levels have been achieved for second and third harmonics. The results show high performance for the proposed power divider.

Design of miniaturize flexible wideband frequency selective surface for electromagnetic shielding application

In this paper, a flexible, ultra-thin, miniaturized broadband frequency selective surface (FSS) is demonstrated for wideband electromagnetic shielding application. The unit cell of the proposed FSS structure consists of cross dipoles loaded with the metallic circular strip. The proposed miniaturized FSS structure has an extremely low profile with a thickness of and a unit cell size of . This FSS structure provides wideband shielding of more than 20 dB from 1.1 to 2.6 GHz frequency region. Besides this wide stopband, the FSS structure acts as a transparent window in the frequency band which can be used for the 5G communication purpose. Moreover, by comprehending the interaction between the incident electromagnetic wave and unit cell, a conceptual equivalent circuit model is developed that helps to interpret the mechanism of the miniaturization as well as the broadband response of FSS structure. We also compared the proposed FSS with other recently reported structures and observed more than 55% improvement in size reduction with several other miniaturized flexible FSS structure. Furthermore, this FSS structure exhibits 20 dB attenuation over a wide frequency region with a fractional bandwidth of 111%. Moreover, excellent resonant stability is achieved in regards to different polarization and incident angle up to .

Dual composite right/left‐handed unit with improved spurious performance and its application in wide‐stopband bandpass filter

AbstractA compact dual composite right/left‐handed (D‐CRLH) unit with improved spurious performance is presented in this study. The proposed D‐CRLH unit consists of an interdigital capacitance (IDC) and a microstrip section inductor (MSI). Compared with the traditional IDC, the proposed IDC is improved by connecting the ends of the alternate fingers through the metallic paths on the back of the substrate. Thus, the spurious resonance at low frequency is eliminated and the usable bandwidth of the IDC is extended. The meander slots are also exploited in each finger of the IDC to increase the series capacitance, which contributes to reducing the circuit size. Furthermore, the proposed D‐CRLH unit is applied in the wide stopband bandpass filter (BPF) design to demonstrate its practicability. The BPF is fabricated and measured for demonstration. The measured results are in good agreement with the simulated results.

A Selective Wideband Bandpass Filter With Wide Stopband Using Mixed Lumped-Distributed Circuits

In this brief, a wideband bandpass filter with extremely wide spurious-free stopband and high selectivity is presented. The filter consists of a wideband bandpass cell cascaded with sharp-rejection wide-stopband low-pass filters (WSLPFs), both designed using a mix of lumped and distributed elements. The proposed wideband bandpass cell, consisting of two series LC resonators and shunt-connected open-ended microstrip stubs, produces a three-pole passband with two transmission zeros on its opposite sides. The LC resonators provide suppression of spurious transmission peaks arising due to the main stub, which is further enhanced by the auxiliary stubs in the wideband cell and the WSLPFs. The design technique imbibes the effects of the self-resonating frequencies of the lumped components, and thus enable the filter to achieve the stopband extension irrespective of their size and make. A prototype of the proposed filter, designed at 1.25 GHz with 62.4% bandwidth, shows the stopband extended up to 18.6 times the center frequency with minimum rejection of 19 dB. The selectivity factor of the passband, defined as the 3-dB to 30-dB bandwidth ratio, is 0.65. The maximum filter dimension is less than a quarter of the wavelength at the center frequency, providing a miniature design.