Wide Stopband Research Articles

A novel compact CPW tunable stop band filter using a new Z-DGS-resonator for microwave applications

The paper presents a novel very compact CPW bandstop filter. The designed structure consists of one unit of new Z-DGS resonator, placed on top layer of ground plane between the input and output this structure, which is excited by 50 ohm coplanar line. The designed filter can be used in X-Band applications as the band stop can be shifted to any other desired frequency by tuning the length of the Z-DGS. The proposed filter topology has as benefits good performances in terms of wide stop-band rejection, low insertion loss, high return loss, simple design and more small size (17.908 × 10 mm2) compared to other previous works those reported in literature. The stop-band width is from 3.96GHz to 6.21GHz, exhibits a 22,25 dB rejection bandwidth of 45% with high selectivity characteristic at the center frequency of 5.05 GHz.

A Simple, Compact Filtering Patch Antenna Based on Mode Analysis With Wide Out-of-Band Suppression

A simple, compact filtering patch antenna with wide out-of-band suppression is presented, where the filtering mechanism is first analyzed and implemented based on mode analysis of a conventional patch antenna. According to the mode analysis, undesired higher-order modes can be effectively suppressed by selecting a proper length ratio of two sides of the patch and the feeding position, thus realizing a wide upper stopband. To further enhance the filtering response, another two simple filtering structures loaded on the patch antenna are also proposed. First, a split-ring-shaped slot is etched on the patch to generate a radiation null at the lower-band edge for improving skirt selectivity. Second, a U-shaped strip is etched underneath the patch and connected with the feeding probe, which can introduce another null at the upper band edge. As a result, a high suppression level of 23 dB in lower and upper stopbands can be realized, respectively, for the proposed filtering antenna, while the upper stopband can extend up to $2.3 f_{0}(f_{0}$ is the center frequency of the antenna). Furthermore, wide passband response can also be achieved by the extra in-band resonances existing in the slot and the strip. A filtering antenna prototype is fabricated and measured for demonstration. Good agreements between the simulated and the measured results are observed, indicating a large impedance bandwidth of 22.6%, high antenna efficiency of 95.6%, and an average gain of about 7.4 dBi. Compared with the reported filtering antennas, the proposed filtering antenna can achieve better wideband filtering response but with a simpler configuration.

A Filtering Power Divider with Tunable Center Frequency and Wide Stopband

AbstractIn this paper, a tunable power divider (PD) with a good band-pass filtering response using quarter-wavelength stepped impedance resonators (SIRs) is presented. By appropriately adjusting the impedance and electrical length ratio of SIR, the proposed structure can achieve wide stopband performance. Meanwhile, four varactor diodes are loaded to the external resonators to achieve electrical reconfiguration. In addition, a pair of transmission zeros (TZs) can be generated by applying source and load coupling on each side of the passband, which can effectively improve passband selectivity and out-of-band rejection. In order to verify the feasibility of the proposed design method, a prototype circuit of the proposed filtering power divider (FPD) with tunable center frequency is simulated, fabricated and measured. A good agreement between the simulation and measurement results is observed.

Optical thin-film filter design with Bragg pair constraint and a divide-and-conquer approach for reduction of the Brewster hole.

Bragg pairs are used as fundamental units to realize optimized thin-film structures. This method is efficient in designing for a large number of layers, such as in a bandpass filter or an edge filter with a relatively wide stopband or angular range. It adapts readily to conventional optimization methodology (such as genetic algorithms). In this paper, the method is first illustrated by application to a conventional high-pass coating on glass, using one set of Bragg pair materials. This demonstrated a 10% improvement over an alternative design technique. A second example is demonstrated using two sets of Bragg pair materials, designed with a more complex merit function, to increase the reflectance around the Brewster angle for p-polarized light. This demonstrated a 19% average reflection improvement across the stopband compared to a two-material design.

Synthesis and Design of LTCC Filtering Balun With Wide Stopband

This brief presents a synthesis method to design compact low temperature co-fired ceramic (LTCC) filtering balun with harmonic suppression. To achieve wide upper stopband, the design equations are driven based on the schematic. Benefiting from the three-port synthesis method and the flexible 3-D layout on LTCC technology, the coupling matrices at the second and third harmonics are manipulated to achieve the harmonics suppression without extra circuits. Meanwhile, the coupling elements of the passband can keep their desired values. A LTCC filtering balun is designed and implemented for demonstration. A 20 dB stopband rejection from $1.2{f} _{0}$ to $4.1{f} _{0}$ is observed. Good agreement between simulated and measured results verifies that the proposed method is suitable and the LTCC technology is reliable for wide stopband filtering balun designs.

Phononic band gaps by inertial amplification mechanisms in periodic composite sandwich beam with lattice truss cores

In order to acquire multiple and wider stop bands in periodic sandwich lattice, this work applies the inertial amplification mechanisms to the composite sandwich beam with pyramidal truss cores and presents a theoretical study on the wave propagation characteristics of the proposed sandwich lattice. An analytical model based on the plane wave expansion method and the Galerkin method is developed to investigate the dispersion relation of transverse waves propagating through the sandwich beam, whose validity is verified by the numerical simulations of spatial decaying performance predicted by the finite element method. Numerical results of complex band structures show that the proposed sandwich beam can obtain multiple stop bands and possess much wider bandwidth. Employing the developed model, the effects of varying attached substructure, the layout of truss members and the material damping on the attenuation performance are discussed to show the flexibility and to obtain thorough understanding of the system.

Graphene Quantum Dot Vertical Cavity Surface-Emitting Lasers

Nonzero-bandgap graphene quantum dots (GQDs) are novel optical gain materials promising for solution-processed light sources with high cost efficiency and device performance. Currently, there have only been a few reports on the realization of GQDs-based lasers. Herein, we demonstrate for the first time room-temperature lasing emission with green gamut from GQDs in a vertical optical cavity composed of Ta2O5/SiO2 dielectric distributed Bragg reflectors (DBRs). The lasing is enabled by the unique design of the DBR, which not only provides a wide stopband spectrally overlapping with the emission of the GQDs but also allows high transmittance of optical excitation in the UV-light region. This demonstration is a clear evidence of the use of GQDs as optical gain materials and represents an important step forward toward their potential applications in wide-gamut laser displays and projectors.

Investigation of Bragg gratings in planar hybrid metal–insulator–metal plasmonic waveguide using graded profile

The design of integrated components using hybrid plasmonics is attracting a widespread interest in the recent years. This work proposes a consistent approach to design Bragg gratings employing the concept of graded profile in a planar hybrid metal–insulator–metal plasmonic waveguide. A comparative study of various width modulations such as triangular, parabolic and rectangular profiles is presented. The most striking observation is that Bragg gratings with parabolic profile offer best performance in terms of compact track length (3.48 μm), wide stopband (168 nm) and good transmission characteristics with fewer side lobes. Additionally, a nanocavity analysis is performed by introducing a defect length of 140 nm in the Bragg grating structure with parabolic profile. A peak transmission of 89% is observed at the resonance wavelength of 1550 nm.

Single-/Dual-BPF Using Coupled-Line Stepped Impedance Resonators (CLSIR)

This brief presents a new coupled-line stepped impedance resonator to design single-/dual-bandpass filters (BPFs). To verify the validity of the design concept a single-band filter with central frequency at 5.2 GHz and a dual-BPF with central frequencies at 3.2 and 5.2 GHz were fabricated and tested. Measured results show low insertion loss (less than 0.8 dB) for the single-band BPF with passband centered at 5.2 GHz with −3 dB fractional bandwidth (FBW) of 9.49% and a dual-band BPF with two passbands centered at 3.2/5.2 GHz with lower and higher passband insertion loss less than 0.6 dB and 0.8 dB respectively, having −3dB FBW of 16.2%/8.2%. The single-band BPF can be used for IEEE802.11a systems, and the dual-band can additionally be used for WiMAX applications. Unwanted spurious frequencies for the two BPFs are cancelled by transmission zeros produced by means of open-ended stubs resulting in extremely wide upper stopband. A thorough derivation is conducted to extract the resonating modes, which are calculated analytically.

Nonperiodic Flipped EBG for Dual-Band SSN Mitigation in Two-Layer PCB

Several electromagnetic bandgap (EBG) structures have been designed to mitigate simultaneous switching noise (SSN) problems in dual bands in wireless local area networks (WLANs). In order to be applicable to two-layer printed circuit boards (PCBs), a novel flipped structure is introduced, which also creates slots for a wide stopband. This article proposes a $2 \times 2$ nonperiodic flipped-EBG (FEBG) for dual-band SSN mitigation in the WLAN, exhibiting noise suppression of 21 and 26 dB in 2.4–2.6 and 5–6 GHz bands, respectively. The simulation results are in good agreement with the experimental data. In addition, a method of positioning optimization is introduced as well to demonstrate the application of the FEBG on a two-layer PCB.

Tunable SIW Bandpass Filters With Improved Upper Stopband Performance

This brief propose the design and measurement of tunable, highly selective and wide-stopband microwave filters using substrate integrated waveguide (SIW) technology. A two pole filter is designed using optimized cavity parameters. Two higher order (4-pole) filters are designed by connecting two cavities vertically and horizontally through coupling slots. In this way, four poles are achieved in two cavities, in which the proposed filter produces $2\times \text{N}$ poles in N cavities. A varactor diode is employed in both configurations to make the filters tunable. The proposed filters have wide upper stopband performance [20 dB up to $4.8f_{1}$ (Filter 1) and 20 dB up to $4.2f_{1}$ (Filter 2)], lower insertion losses [0.2-1.1 dB (Filter 1) and 0.2-1.5 dB (Filter 2)] and good tunability ranges [2.7–3.4 GHz (Filter 1) and 3.1–3.9 GHz (Filter 2)]. In order to validate the proposed design, a prototype is fabricated on RT/duroid 5870 substrate and measured. The simulated results accord closely with the measured results.

A novel compact lowpass filter with sharp roll-off and wide stopband

AbstractIn this paper, a microstrip lowpass filter adopting two main resonators with steep transition band and wide rejection band has been introduced. The first main resonance cell consists of meandered transmission lines which are loaded by modified T-shaped patches. The second main resonator is composed of high-impedance lines loaded by polygon patches. To obtain a steep skirt performance, the first and second resonators have been combined. Moreover, employing eight high–low impedance folded stubs and two rectangular open-stubs as suppressing cells has resulted in improving the stopband features. To comprehend the frequency behavior of the employed resonators and also their combination, the formulas of the transmission coefficient, reflection coefficient, and the transmission zeros of their equivalent LC circuits have been extracted, separately. According to the measurement results, the −3 dB operating frequency of this filter is 1.65 GHz. Moreover, a relative stopband bandwidth equal to 166% with a corresponding attenuation level of 23 dB and a sharp roll-off rate (393.61 dB/GHz) have been achieved. In the passband region from DC to 1.632 GHz, the insertion loss and return loss are better than 0.0763 and 15.85 dB, respectively, proving an acceptable in-band performance. Finally, the implemented structure brings about a high figure-of-merit equal to 81 672.

Design of compact single‐ended‐to‐balanced filtering power divider with wideband common‐mode suppression

A new design of single-ended-to-balanced (SETB) filtering power divider (FPD) with wideband common-mode (CM) suppression is presented. To effectively realise high suppression of CM noise, a hybrid structure constructed by both the double-side parallel-strip line (DSPSL) and a half-mode defected ground structure (HMDGS) serving as the mid-inserted conductor plane are adopted. Besides, due to the effect of HMDGS, the rejection of second harmonics for the differential-mode (DM) transmission is also improved. Meanwhile, by employing two pairs of dual-mode resonators symmetrically coupled with a stepped-impedance input feed line and adding a DSPSL stub, wideband-filtering performance with high selectivity is achieved. For validation, a prototype of the proposed SETB-FPD centred at 5.9 GHz with a 3-dB fractional bandwidth (FBW) of 27% is designed, fabricated and measured. Results indicate that the proposed SETB FPD exhibits good performances of high selectivity, wide upper stop band, good isolation between two balanced output ports and 30-dB suppression of CM noise over the DM pass band.

Highly confined radial contour modes in phononic crystal plate based on pillars with cap layers

We investigate highly confined and isolated surface modes in a phononic crystal plate based on pillars with cap layers. The structure is made of a thin membrane supporting periodic pillars each composed of one cylinder surmounted by a disk shaped cap layer. An optimal choice of the geometrical parameters and material composition allows the structure to support isolated radial contour modes confined in the cap layer. In this study, we consider diamond and gold (Au) as the pillar and cap layers, respectively, and aluminum nitride as a thin membrane owing to the strong contrast in their elastic and density properties and to their compatibility with the integrated circuit technology and microwave electroacoustic devices. The phononic crystal based on diamond pillars allows us to induce a wide stop band frequency, and the addition of the Au disk shaped layer on diamond pillars enables us to introduce flat modes within the bandgap. We demonstrate that one can optimize the flat mode frequencies by varying the geometrical parameters of the Au cap layer. The quality factor (Q) of a cavity resonator composed of one line gold/diamond pillar surrounded by an array of diamond pillars on both sides has been investigated. These results clearly show that, using this design approach, one can (i) reduce the acoustic energy leakage out of the resonator and (ii) optimize the cavity resonator’s Q factor by varying only the geometrical parameters of the gold cap layer. The proposed design provides a promising solution for advanced signal processing and sensing applications.

Overall Study of Frequency-Agile Mechanism of Varactor-Loaded <italic>λ</italic>/4 Resonator for Designing Tunable Filter With Stable Wide Stopband

This paper presents an overall investigation of the frequency-tuning mechanism of the varactor-loaded λ /4 stepped impedance resonator (SIR). The relationships between the tuning ranges of the resonant frequencies (fundamental frequency $(f_{1})$ and harmonics) and the basic parameters of the varactor-loaded SIR are theoretically analyzed and given in detail. It can be found that the loading location of the varactor and the SIR parameters (characteristic impedances and length ratio of the two sections) have significant effect on the frequency-tuning range. Benefiting from the discriminating responses of $f_{1}$ and $f_{3}$ (third harmonic) to the loading location of the varactor, $f_{1}$ can be well tuned as the varactor's capacitance changes while $f_{3}$ is fixed, when the varactor is loaded at the voltage-null point of $f_{3}$ on the λ /4 SIR. Thus, a stable wide stopband can be achieved due to the fixed $f_{3}$ , which acts as the lowest spurious in the design of tunable filter. For demonstration, a second-order tunable filter with stable wide stopband and constant fractional bandwidth is implemented and measured. In the tuning process of the passband operating at $f_{1}$ , the lowest spurious resulting from $f_{3}$ is immobile, which is always more than ${\text{4}}f_{1}$ . The simulated and measured results with good agreement are presented to verify the theoretical predictions.

LTCC Bandstop Filters With Controllable Bandwidths Using Transmission Zeros Pair

This brief presents compact low temperature co-fired ceramic (LTCC) bandstop filters (BSFs) using internal coupled lines. The inband transmission zeros pair (TZP) is generated by introducing internal coupling. According to the guidelines obtained by theoretical analysis, the bandwidth could be flexibly controlled. Furthermore, the roll off and the passband performance can be improved. To demonstrate the proposed method, LTCC BSFs with narrow and wide stopbands are implemented and measured. The broadside couplings on LTCC multilayers technology are employed to realize the internal couplings and the TZPs. The good consistency of the simulated and measured results supports that the proposed method is suitable not only for the narrow- but also for the wide-band BSF designs.

Miniaturized low‐pass filter design with wide stopband using complementary split‐ring resonator

AbstractA miniaturized microstrip low‐pass filter (LPF) design comprises of meander lines, rectangular patches, open‐circuit stubs, and a complementary split‐ring resonator placed in between the input/output ports has been presented in this article. The proposed filter has insertion loss of 0.10 dB in passband with a bandwidth of 3.8 GHz. It also has a wide stopband bandwidth of 9.9 GHz with minimum attenuation of 28 dB (between 4.1 GHz and 14 GHz). Wide stopband has been achieved by introducing the open stubs and impedance transforms the patch resonators. Group delay of designed LPF quantified to be less than 0.22 ns in the passband. The simulated and measured results have been compared and found to be in good agreement. This filter finds its applications in Global System for Mobile Communications (GSM) and the industrial, scientific and medical (ISM) bands with harmonic suppression in modern communication receivers.

A Lowpass Filter Design Using Curved and Fountain Shaped Resonators

AbstractIn this paper a new lowpass filter (LPF) with curved line resonators and fountain shaped resonators is proposed. The proposed filter has achieved wide stopband, compact size, sharp roll-off rate and low return loss. Two tapered resonators are used to produce transmission zeros and widen the stopband. Also, a fountain shaped resonator is proposed using curved transmission lines to obtain good sharpness in the filter response. The cut-off frequency of the designed LPF is 1.74 GHz and the overall size of the designed LPF is 0.135 λg × 0.132 λgwhere λgis the guided wavelength at the cut-off frequency. The results show that the overall size of the lowpass filter could be reduced using curved line resonators and curved transmission lines.

Compact low‐pass/band‐pass filters based on quarter‐mode substrate integrated waveguide and a connected network of CSRRs

In this study, a compact low-pass filter (LPF) and two compact dual-wideband band-pass filters (BPFs) are proposed based on a connected network of complementary split-ring resonators (CSRRs) and open CSRRs (OCSRRs). The LPF is designed based on microstrip structure, and then the structure is changed to quarter-mode substrate integrated waveguide for designing the dual-band BPFs. The 3 dB cutoff frequency of the LPF is 1.84 GHz and its size is 0.094λ g × 0.094λ g , where λ is the guide wavelength at 3 dB cutoff frequency. The LPF has a wide stop-band, up to 16 GHz. The first proposed dual-wideband BPF has the centre frequencies of 3.85 and 8.03 GHz, with 3 dB fractional bandwidths of 31.69 and 13.7%, respectively. Finally, a sharper dual-band BPF is obtained by cascading two proposed dual-wideband BPFs and optimising them for the desirable response. The measured centre frequencies of the second dual-band BPF are 3.65 and 7.15 GHz with 3 dB fractional bandwidths of 28.21 and 12.52%, respectively. The measurement results of the fabricated filters are in good agreement with the simulation ones. The filters are compared with similar reported filters in the literature, which confirm the compactness of the proposed filters..

Compact ultra-wideband bandpass filter based on composite right/left-handed transmission line with improved out-of-band performance

ABSTRACTThis paper presents a novel compact ultra-wideband (UWB) bandpass filter (BPF). It consists of two composite right/left-handed transmission line (CRLH-TL) unit cells and an anti-coupled line structure. The CRLH-TL unit exhibits good passband performance with a compact size. By cascading the anti-coupled line structure, a wide upper stopband is obtained. The measured fractional bandwidth and insertion loss are 113.9% and 0.52 dB, respectively. Moreover, a broad stopband from 14 to 30 GHz with a high rejection level of 20 dB is obtained. The whole size is 14.4 mm × 10.2 mm. The simulated and measured results agree well.