Wide Stopband Research Articles

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.

Stacked lightweight metasurfaces for wider stopband in X-K band

Frequency selective surfaces printed on optically transparent, large-area, flexible plastic sheets are studied for their passband and stopband characteristics when present as single-layer, two-layer and three-layer stacks. The unit cell design, its size, spacing and thickness on the substrate enable the single layer metasurface to yield a stopband width of 4.46 GHz (corresponding to 34.80%), when the center frequency is at 12.83 GHz in simulation and 12.86 GHz in measurement. On stacking identical surfaces as two-layer and three-layer configurations with suitable displacements both within the surface plane and perpendicular to the surface plane, the structural geometry of the unit cell gets varied leading to an ultra-wide stopband of 8.96 GHz in the range from 12.16 GHz to 21.11 GHz which covers X to K band. This leads to a wider stopband width of 43.60% for two-layer stack and 48.10% for three-layer stack with no in-plane shift. This is further enhanced to 65.50% with suitable shift within the plane of the stacked design. The three-layer stacked structure is ultra-thin with a thickness of 0.012 λ0. The single layer as well as all the three stacked structures have stopband characteristics that are invariant to incidence angle variation up to 750.

Improving the Response of a Bridged-T RC Network

The paper presents a modification of a bridged-T RC network, originally proposed by Sulzer, for increasing the stop bandwidth and decreasing the notch level in the frequency response, which also gives the facility for fine tuning the notch frequency. It uses the well-known dual input technique.

Wideband electromagnetic interference filtering power divider with a wide stopband using the genetic algorithm

This paper proposes a new design of an electromagnetic interference wideband filtering power divider (FPD) with a wide stopband based on the genetic algorithm (GA). A set of data structures is constructed by describing the corresponding connection method between the basic units and their electrical parameters in the three-port design. Then, the GA is used to find the appropriate design topology and electrical parameters, including isolation resistances, to meet FPD specifications by optimizing the data structures. For validation, one prototype is implemented. The results indicate that the new wideband FPD exhibits compact size, sharp roll-off, and good in-band isolations.

An Ultra Compact Microstrip Branch Line Coupler with Wide Stopband Using LCL Filter and Meandered Stubs for Microwave Applications

A branch line coupler (BLC) with ultra-compact size and harmonic suppression ability using an LCL filter and meandered stubs is proposed in this paper. There are some important factors in microstrip coupler design, including size reduction, harmonic suppression, and low insertion loss. Thus, improving each of these factors will contribute to a more efficient design. In the proposed circuit, for the first time, LCL filters, including four T-shaped circuits and four meandered line open-ended stubs, were used together to reduce the circuit size and suppress unwanted harmonics. The proposed LCL filters, incorporated in the BLC branches, resulted in superior size reduction and harmonic suppression for the presented BLC. The proposed BLC correctly worked at 900 MHz with 300 MHz operating bandwidth, which showed 33% fractional bandwidth (FBW). Additionally, a wide suppression band from 1.4 GHz to 8.8 GHz, with more than 20 dB attenuation level was obtained, which suppressed the second to ninth unwanted harmonics. The overall size of the proposed 900 MHz coupler was only 11 mm × 10.4 mm (0.044 λ × 0.042 λ) while the size of the conventional 900 MHz coupler was 61.5 mm × 62.5 mm (0.25 λ × 25 λ). The proposed BLC had a very small size and only occupied 3% of the size of the conventional coupler, which corresponded to a 97% size reduction. To the best of the authors’ knowledge, to date, the best size reduction has been obtained among the published couplers. Furthermore, the experimental results verified the simulated and analyzed results of the proposed technique and demonstrate its potential for improving the performance and miniaturizing the size of other similar BLCs.

Design of a dual-band filter with high selectivity and wide stopband

ABSTRACT This paper proposes a design of dual-band bandpass filter with a high selectivity and a wide stopband, by using two ring type hairpin resonators. The equivalent circuit of the used resonator is analyzed through the analysis of odd and even modes. The designed filter can achieve dual passbands at 2.4 GHz and 3.65 GHz for wireless local area network (WLAN) and 5 G communication systems, with transmission zeros at 2.9 GHz and 5.1 GHz, realizing high selectivity. With a wideband bandstop filter on the input port, a wide stopband from 4.6 GHz to 17.3 GHz is realized.

A Miniaturized wide Stopband Low-pass Filter using T and Modified L Shapes Resonators

A new structure of microstrip-based low-pass filter with wide stopband and sharp roll-off is introduced, in this paper. In the proposed topology, resonators with T and modified L Shapes have been used. To improve the suppression factor and relative stopband bandwidth, the second resonator has been added to the first resonator. The designed filter has been fabricated on a 20 mm thickness RO4003 substrate, which has a loss tangent of 0.0021 and a relative dielectric constant equal to 3.38. All parameters including roll of rate, stopband, bandwidth, return loss, insertion loss, and figure of merit have significant coefficients. Simulation has been ran using advanced design system software. The 3dB cutoff frequency is appropriate. The value of the insertion loss parameter is &lt;0.1 dB and the S11 parameter is −22 dB at this point. The stopband is extended from 2.42 up to 24 GHz, which shows an ultra-stopband. The results of the simulation and experiment are almost similar, which indicates a proper performance of the designed structure.

Optimization and Design of Balanced BPF Based on Mixed Electric and Magnetic Couplings

A balanced bandpass filter (BPF) with an improved frequency selectivity for differential-mode (DM) excitation and high rejection for common-mode (CM) excitation is proposed in this paper. Two half-wavelength stepped impedance resonators (SIRs) are employed based on mixed electric and magnetic couplings to realize a DM passband centered at 2.48 GHz. The center frequency and bandwidth can be easily controlled by optimizing the dimensions of SIRs and the coupling between them, respectively. Meanwhile, two transmission zeros (TZs) are generated based on the mixed electric and magnetic couplings and are independently controlled by tuning the coupling strength. Moreover, a wide DM stopband can be realized by optimizing the SIRs. The proposed balanced BPF is fed by balanced U-type microstrip–slotline transition structures, which can achieve high wideband CM rejection without influencing the DM responses, and the design complexity can be clearly reduced. Finally, a balanced BPF is fabricated, and a good agreement between the simulation and the measurement is observed, which verifies the design method.

A novel filtering monopole antenna for 5G communications

PurposeThis study aims to design a compact filtering monopole antenna for 5G communication. The design is most suited for various applications within the frequency range of 2.2–3.8 GHz. It offers enhanced bandwidth and reasonable gain with wide-stopband performance.Design/methodology/approachA low-pass filter (LPF) of complementary split ring resonator (CSRR) with short-circuited stub lines is integrated with a compact defected coplanar waveguide fed truncated circular monopole ultrawideband (UWB) antenna. The reference UWB antenna etched on an FR4 substrate was coupled to the designed LPF to transform the UWB antenna into a wideband antenna. The effect of coupling is analyzed based on the real and imaginary responses of the terminal impedance (ZT) curve. Three short-circuited stub lines of asymmetric lengths are added to the CSRR LPF to suppress harmonics, thereby enhancing the stopband performance and impedance matching between the elements. The proposed filtering antenna is fabricated using a photolithography process, and the corresponding results are measured using a network analyzer (N9951A). The radiation parameters of the proposed filtering monopole antenna are tested in the anechoic chamber. The simulated/measured results are compared and are found in agreement with each other.FindingsThe proposed design suppresses 6.5f0 harmonics, resulting in wide stopband performance and increased gain selectivity at the transition edge. A peak suppression of −41 dB and an average suppression of −18 dB were attained throughout the stopband. An operating fractional bandwidth of 54.5%/143% with a peak gain of 3 dBi/5 dBi was obtained. The proposed filtering antenna supports 5G applications such as WiMAX, WLAN, n7, n38 IMT-E, n30 WCS, n40 TDD, n41 TDD, n48 TDD, n78 TDD and n90 TDD.Originality/valueThe proposed design is novel and compact and has a wide application in 5G communication. With the filter, the antenna operates in wideband, and without the filter, it operates in UWB. Besides, it offers enhanced stopband performance with high gain selectivity at the transition edge. Comparatively, a 50% improvement in bandwidth, 52% improvement in size reduction and 33% improvement in harmonic suppression are attained.

Compact LTCC filter with wide stopband for 5G applications

AbstractA compact bandpass filter (BPF) is proposed with dual composite right/left‐handed resonators for the fifth‐generation (5G) N79 band applications. With consideration of compact size and filtering performance simultaneously, the vertical and horizontal finger constructed capacitor is improved with respective dimensions for each finger to obtain larger capacitance and better filtering performance. The proposed BPF is built in a four‐layer low‐temperature co‐fired ceramic substrate and possesses a smallest reported size of only (). The measured in‐band insertion loss (IL) is better than and a wide out‐of‐band suppression higher than upto are both achieved. Finally, comparison and discussion are implemented as well.

On-Chip mm-Wave Second-/Third-Order BPF and Balun With Wide Stopband and Low Radiation Loss Using SIDGS Resonators in 40-nm CMOS

In this article, two millimeter-wave substrate-integrated defected ground structure (SIDGS) resonators are proposed for filters and balun implementation. Such SIDGS resonators are composed of defected ground structure (DGS) with grounded shield and surrounding vias, which not only exhibit wide stopband with low radiation loss but also are flexible to integrate with active circuits. Using different coupling methods, second-/third-order bandpass filters (BPFs) and filtering balun are designed based on the proposed SIDGS resonators. The filters and balun are fabricated in a standard 40-nm complementary metal-oxide-semiconductor (CMOS) technology. The second-order filter is centered at 28 GHz with an insertion loss of the 2.7-and 3-dB FBW of 20.4%. Meanwhile, the stopband extends to 140 GHz with a rejection level of 30 dB. The third-order filter operates at 28 GHz with an insertion loss of the 2.9-and 3-dB FBW of 47%. Meanwhile, the stopband extends to 170 GHz with a rejection level of 27 dB. The filtering balun operating at 25 GHz with the 3-dB FBW of 32% exhibits in-band amplitude/phase imbalances of 0.6 dB and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\pm$</tex-math> </inline-formula> 1.1 <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> , respectively. The minimum in-band insertion loss is 2 dB excluding the theoretical 3-dB loss. The stopband extends to 175 GHz with a rejection level of 30 dB.

A compact, flexible and transparent UWB bandpass filter with silver nanowires

The advent of ultra-wide band (UWB) technology has made bandpass filters omnipresent. Current approaches to designing bandpass filters cannot provide transparent and flexible bandpass filters to meet their increasing demands for various applications. In this new work, a flexible and transparent UWB bandpass filter with silver nanowires printed on flexible polyethylene terephthalate (PET) substrates is designed. The filter structure is formed by connecting three pairs of open-circuited rectangular stubs. Proper coupling of these stubs is used to obtain the desired UWB passband. The proposed design operating from 1.05 to 10.75 GHz with an extremely wide stopband up to 50 GHz and a rejection level of 11.4 dB is demonstrated in the measured results. Furthermore, it was observed that the measured results matched well with the simulated results. These improved results indicate that our design strategy will provide a way to design highly efficient flexible UWB filters. This flexible filter may serve as a potential candidate for increasing the flexibility of indoor electronic applications.

Wideband Dual-Polarized Differential-Fed Filtering Microstrip Patch Antenna with High Suppression and Wide Stopband

This paper presents a wideband dual-polarized filtering antenna with high suppression level and wide stopband. In the proposed antenna, the driven patch operates in a TM10 mode with an inherent radiation null caused by a higher mode TM12. Four dual-strip structures connected with the feeding probes are placed below the driven patch to achieve the capacitive coupling, thus resulting in a low-frequency radiation null with a sharp roll-off rate. The introduction of the parasitic patch and strips generates an in-band resonance and two high-frequency radiation nulls, which widens the upper stopband. Four slots are etched on the driven patch to excite the third resonance, thus achieving the wide operation band. The prototype of the proposed antenna is fabricated. With four controllable radiation nulls, the out-of-band suppression levels are above 29 dB in low-frequency band greater than 1 GHz and above 21 dB in high-frequency band up to 7 GHz, respectively. Due to the three in-band resonances, a wide impedance bandwidth of 2.93-3.96 GHz with a fractional band of 30% is obtained. With the rotational symmetry structure driven by differential probes, the proposed dual-polarized antenna has a cross-polarization ratio better than 28 dB, a high polarization isolation above 43 dB, and a good peak gain about 9.9 dBi.

Realization of a novel dual-band bandpass filter with coupled series gaps and stepped impedance complementary split ring resonators

In this article, a bandpass filter (BPF) is proposed by etching stepped impedance complementary split ring resonators (SICSRRs) pairs in parallel with series gaps on the top side of a coplanar waveguide (CPW). The Nicolson-Ross-Weir (NRW) method is used to analyze the left-handed (LH) behavior of the filter. The effects of the resonators parameters on the left-handed BPF are studied. The parameters and number of the resonators are adjusted properly to obtain the desired filter characteristics. Split ring resonators (SRRs) are magnetically coupled to the BPF to realize a novel left-handed dual-band bandpass filter. Besides, The dual-band filter is described by means of the lumped-element equivalent circuit model. Also, the quasi-static analysis is used to obtain the equations for the resonant frequencies of the resonators. The efficient electrical size of the dual-band filter is 0.51λg × 0.42λg where λg represents the guided wavelength at the first passband center frequency. The prototype of the compact dual-band BPF is fabricated and measured. The measured results reveal low insertion loss and high return loss at the passbands along with wide upper stopband attenuation. The measured result is in a good agreement with the corresponding simulation result.

A miniaturized highly selective MTM‐inspired filter for lowpass and triple‐band bandpass performance with configurable transmission zeros and bandwidth

SummaryThis paper presents a novel, compact, and highly selective metamaterial inspired filter with low insertion loss, lowpass, and triple‐band bandpass characteristics. The presence of five transmission zeros and seven poles facilitates highly selective filtering performance. The improved impedance matching and transmission characteristics have been achieved by embedding complementary split ring resonator as defected ground structure. The filter circuit area excluding 50 Ω feed lines is merely 0.17λg × 0.05λg at 3‐dB cut‐off frequency of lowpass passband (1.11 GHz). The 3‐dB fractional bandwidths of the three bandpass regions are 39.50% (1.3–1.94 GHz), 21.20% (3.12–3.86 GHz), and 21.06% (4.04–4.99 GHz) at the center frequencies of 1.62, 3.49, and 4.51 GHz, respectively. Intended filter also offers a wide stopband extending from 2.15 to 2.96 GHz at close to 20 dB attenuation level. Further, position of transmission zeros and 3‐dB passband bandwidths can be adjusted by carefully choosing structural design parameters. The metamaterial effect of the proposed filter has been demonstrated by plotting refractive index followed by validating the performance with the help of experimental measurements. No filter shows lowpass characteristic along with three bandpass performances as found by the authors exploring literature, which presents the novelty of the proposed work.

Theoretical optimization of cavity configurations for fiber lasers: enhancement of mode oscillation and slow-light effect

This article theoretically investigates the optimization of various fiber Bragg cavities for sustaining laser oscillation and amplification in fiber lasers designed as distributed feedback reflectors and/or distributed Bragg reflectors. Coupled mode theory with the transfer matrix method have been used to obtain reflection and transmission spectra as well as group delay and dispersion for characterizing the proposed cavities. The optimum configuration gives symmetrical spectra with single-mode oscillation in the stop-band manifesting an enhanced slow-light process. Various cavity parameters such as cavity configuration, length, pitch, and structure of the grating are found to have a significant effect on the field confinement, oscillated modes, and dispersion of the spectrum. Cavities formed by phase-shifted FBGs showed better photon confinement, and better reinforcement of single-mode oscillations. By incorporating an extra etalon-like cavity (etalon), uniform spectra with wider stop-band can be manifested and single-mode oscillations with remarkable delay for the slow-light effect are maintained.

Broadband Magnetoelectric Dipole Filtering Antenna for 5G Application

A magnetoelectric (ME) dipole filtering antenna with high out-of-band suppression level and high selectivity is proposed in this letter. The intrinsic radiation null of the traditional ME dipole antenna is used, which produces a good filtering response at the edge of the lower passsband. A pair of vertical parasitic metal planes are introduced between the shorted walls and fed through slot coupling, which can be equivalent to an additional magnetic dipole. The radiated electric field of the magnetic dipole is opposite to that of the original antenna at higher frequency, forming a wide stopband radiation null, which greatly improves the high-frequency stopband suppression level of the antenna. Furthermore, a pair of T-shaped coupling stubs are inserted between the shorted wall and electric dipole, producing another radiation null with high roll-off rate at higher frequency. The measurement results show that the −10 dB impedance bandwidth of the proposed antenna is 49.4% (3.2–5.3 GHz). Its low-frequency stopband suppression level is greater than 16.6 dB and high-frequency stopband suppression level is greater than 26.0 dB. Moreover, the antenna radiation pattern is stable and symmetrical in the whole operating passband, and the filtering response is desirable.

Compact high-selective wide-stopband coupled bandpass filter using middle-shorted hairpin-resonators

In this letter, a novel compact highly selective coupled bandpass filter (BPF) with sharp roll-off and wide stopband with excellent attenuation is proposed. This BPF is designed using two middle-shorted hairpin-resonators and a slot line resonator. The coupling matrix is calculated theoretically as per the specifications. The coupling coefficients between the resonators are computed by using the full-wave simulator HFSS to properly select the coupling gap between the resonators. The ABCD and S-parameters of the proposed design are computed, and the S-parameters are plotted theoretically. The designed filter is fabricated and tested. Good agreement is found between simulation and measurement. The proposed filter has excellent measured characteristics, including an insertion loss of 1.2 dB, a return loss better than −20 dB, high band edge attenuation of 60 dB, three Transmission Zeros (TZs), and a wide stopband rejection of greater than 30 dB up to 3f0 where f0 is the center frequency of the BPF. The proposed filter can be used for WLAN applications.

Diversity Pertaining to the Attenuation of the RF Disturbance Suppression Power Line Filters

Filters for the suppression of the RF disturbances in power lines are passive; wideband stop filters attenuating common as well as differential disturbances should be insensitive to the variation in the impedance at the input and the output. The design and verification process of such filters differs entirely from that used for the signal RF filters. In the document CISPR 17, entitled “Methods of measurement of the suppression characteristics of passive EMC filtering devices”, two definitions of the attenuation of the common and differential modes are presented. The first is simply direct measurement, and the second is based on a calculation using the single-ended S-parameters of the multiport. These two definitions are the source of diversity. In this paper, we hypothesize that the attenuations achieved with these two methods are identical only if the filter is in perfect balance. Consequently, different attenuations can be achieved. The requirement of balance can be violated due to the tolerances of the components used in the filter. The paper begins with a simple unbalanced four-port, for which analytical formulas are derived. It is also shown that an approach with single-ended S-parameters enables the calculation of the mode conversion between the input and the output, which is called the conversion loss. This is the measure of the grade of the imbalance. Thereafter, the common-mode attenuation of an exemplary RF suppression filter is derived with the presented methods. Additionally, the conversion loss of the filter is calculated. The comparison of the conversion loss with both attenuations is satisfactory, proving the hypothesis formulated in the paper.