Sharp Stopband Research Articles

Wideband Switchable Sharp-Rejection Filter in Compact 3-D Heterogeneous Integration

A switchable bandstop filter (BSF) bank in 3-D heterogeneous integration is presented in this article for multiband applications. Compared with conventional filter banks, the proposed design features wide bandwidth, sharp skirts, compact size, and high integration. In the proposed BSF, double short-ended coupling lines are introduced to expand the operation bandwidth with sharp rejection. Moreover, to significantly reduce the size of the proposed BSFs, an in-house silicon micromachining process is developed to heterogeneously integrate two stacked BSFs with switches by through-silicon vias (TSVs). To experimentally validate the proposed configuration, a two-channel switchable BSF bank is designed, fabricated, and measured. The measured results show a tuning range of 7.95–12.3 GHz (43%), a maximum bandwidth of 30%, and a sharp stopband rejection of 50 dB. These results agree well with simulation. Moreover, the fabricated prototype is only 15 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\times 8\times $ </tex-math></inline-formula> 1 mm3, whereas a typical industrial counterpart is around <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$86\times 74\times18$ </tex-math></inline-formula> mm3, i.e., the size is significantly reduced to 1‱. To the best of the authors’ knowledge, this is the first demonstration of a wideband switchable sharp-rejection BSF chip fully integrated in the TSV process.

Spectrally Selective Optical Loss in Fibers With High-Index Rods Embedded Into Silica Cladding

In this work, we perform a detailed study of a novel type of optical fiber for spectral filtering, which is based on a step-index core with high-index rods embedded into silica cladding. Recently, it was theoretically predicted that such a structure could demonstrate a very sharp stopband due to the resonant core mode interaction with the eigen high-index rod mode. In the current paper, we realize the proposed structure and experimentally confirm its applicability for spectral filtering. In our experiments, we show the possibility of creating a very sharp shortpass fiber spectral filter. In particular, we demonstrate a change in the optical loss of the core mode by two orders of magnitude (from less than 0.1 dB/m to more than 10 dB/m) for a 12 nm wavelength shift (from 1008 nm to 1020 nm) and by more than 3 orders of magnitude (from 0.02 dB/m to 60 dB/m) for a 70 nm wavelength shift (from 980 to 1050 nm). Possible applications of the realized fiber design are discussed. Mechanisms of optical loss in the fabricated structure are studied, and the presence of an additional mechanism, which is not related to absorption in the high-index rods, is revealed.

Compact semi-lumped bandpass filter with sharp rejection

ABSTRACT A novel compact low-temperature-cofired ceramic (LTCC) bandpass filter with sharp rejection and wide stopband is presented in this paper. Semi-lumped resonant cells composed of multilayer ceramic capacitors and via-hole inductors are utilized with source–load coupling, thus two transmission zeros (TZs) can be generated near both sides of the passband, resulting in a high skirt selectivity and wide harmonic suppression. A LTCC bandpass filter works from 2.1 to 2.3 GHz has been designed and fabricated in a four-layer substrate to verify the proposed topology. With an extremely compact size of 2.0 mm × 1.25 mm × 0.9 mm, the design is highly integrated and suitable for miniaturized modern wireless communication applications.

A New Method for Designing Modified Compact Microstrip LPF with Sharp Roll-Off and Wide Stopband

A New Method for Designing Modified Compact Microstrip LPF with Sharp Roll-Off and Wide Stopband

Design of Microstrip Dual-Mode Wideband Bandpass Filter with Controlled Center Frequency and Bandwidth Using Bandstop Filter Topology

ABSTRACT This paper discusses a new method for designing a microstrip dual-mode, sharp skirt, wideband bandpass filter with controlled center frequency and bandwidth from bandstop filter topology. A meander closed loop resonator with directly connected orthogonal feed lines provides a Bandstop filter (BSF) with reduced size. A pair of L-shaped open stubs introduced along the diagonal axis D-D1 realizes a wide passband within the rejection band (0.93–4.13 GHz) of the bandstop filter with sharp stopbands on either side of the passband. Furthermore, the effect of L-shaped open stubs susceptance on passband edges is demonstrated. A quarter wavelength stepped impedance shunt stub (SISS) connected at is proposed to achieve additional transmission zeros in the upper and lower rejection bands to improve the sharpness of filter response. Both center frequency and bandwidth of the proposed filter are controlled by the impedance ratio (R) of the SISS element. The proposed filter is simulated using ADS, fabricated and measured using Vector Network Analyzer (VNA). A good agreement is achieved between simulated and measured results.

A compact SIW bandpass filter using DMS-DGS structures for Ku-band applications

This paper presents a design of compact SIW (substrate integrated waveguide) bandpass filter for application in Ku-band Transmit up-convert frequency (i.e., 13.7–14.1 GHz) used for satellite communications. Based on Defected Microstrip Structure-Defected Ground Structure combination (DMS-DGS), this SIW filter structure is designed to improve passband and stopband performance. By merging circular ring slot (CRS) with interdigital DGS, better passband characteristics with sharp stopband attenuation are obtained. To validate the design, the filter is fabricated using Rogers substrate. The size measures 23.8 mm × 10 mm and operates at a center frequency of 13.9 GHz. Measured results of the filter agree well with the simulated results. Also, designed BPF filter has advantage of low insertion loss, better return loss, compact size and high stopband rejection.

Tri-Band Band-Pass Filter Based on Multi-Mode Spoof Surface Plasmon Polaritons

This paper presents a novel tri-band bandpass filter based on multi-mode spoof surface plasmon polaritons (SSPPs) in microwave frequencies. The combination of multi-mode resonance and cutoff characteristic of SSPPs contributes to a tri-band bandpass response. The proposed SSPPs-based filter consists of two coplanar waveguides, two conversion parts and a SSPPs transmission structure made of five unit-cells. Each unit cell is a multi-mode resonator, which is constructed by a pair of oppositely oriented double-side folded strips, and the ends of folded strips are placed closely to form coupled-stubs. Two distinct passbands divided by a sharp stopband are produced under the cutoff frequency of SSPPs transmission structure. The third passband above the cutoff frequency is introduced by the resonant tunneling effect due to the self-resonant mode of proposed SSPPs unit cell. Dispersion relations, electric field distributions and proposed equivalent transmission line model give a physical insight into the filter operating mechanism. As a demonstration, a prototype of the proposed filter has been fabricated and measured. The measurement results demonstrate that the proposed filter has a tri-band bandpass performance with excellent frequency selectivity, which may be very useful in many applications, such as multi-band wireless systems.

Real-Time Detection of Gas and Chemical Vapor Flows by Silica Inverse-Opals

A silica inverse-opal is fabricated through the co-assembly of silica precursors and mono-dispersed polystyrene particles with a diameter of 287 nm. Then, the polymer face-centered-cubic structure was removed by calcination procedure to obtain a silica inverse-opal offering sharp stop-band around 445 nm. Sensitivity of the sample for static refractive index detection was acquired by its immersion in different water/ethanol mixtures. Furthermore, an experimental setup was designed to evaluate the dynamic response of sample for diverse gas and water vapor flows. Fabricated sample is capable of offering high sensitivities as high as 415 nm/RIU and reversible responsivities as fast as 120 ms. Also, it has been shown that despite reduced sensitivity in dynamic measurements, fabricated silica inverse-opal is able to detect slight refractive index variations and thus very small alterations in gas and vapor flows. According to which, the proposed structure may find numerous applications in remote and non-destructive gas and vapor flow sensing.

Dual‐layer SIW cavity filtering antenna with a controllable radiation band and two radiation nulls

A dual-layer substrate-integrated-waveguide (SIW) cavity filtering antenna with a controllable radiation band and two radiation nulls is proposed. It consists of a coaxial feeding, two SIW cavities, three metal planes and three slots. An H-shaped slot is etched on the top plane and two rectangle slots are cut on the middle plane. A radiating mode (i.e. TE210 mode) is excited to achieve a radiation band while two non-radiating modes (i.e. TE010 mode and TE110 mode) are utilised to generate two radiation nulls. Good filtering performance including sharp sideband selectivity and high stopband suppression is achieved by these radiation nulls. Moreover, the radiation band can be independently controlled without affecting the radiation nulls. A fabricated prototype with the size of 0.58λ 0 × 0.58λ 0 × 0.07λ 0 is measured. The measured centre frequency of the radiation band is at 3.49 GHz with the gain of 5.39 dBi and efficiency of 79.25%. However, the gain and efficiency of a radiation null at 3.29 GHz are −27.56 dBi and 0.07% while those of the other radiation null at 3.86 GHz are −27.29 dBi and 0.04%.

Efficient Analytical Evaluation of Complex Dispersion Relations of a Multiple-Row Periodic Array of Magnetodielectric Circular Cylinders

An analytical mode-matching method based on the common area concept and mixed coordinate formulations is proposed for a multiple-row periodic array of magnetodielectric circular cylinders (PAMCs). Complex dispersion relations for single- and double-row PAMCs are computed with Davidenko’s method and tested using commercial electromagnetic (EM) analysis packages, thus verifying that our solutions are very accurate and numerically efficient. The EM bandgap formations of a single-row PAMC are presented with respect to different cylinder spacing. We also observe that a resonance gap, which results in a sharp band-stop phenomenon, can appear in a double-row PAMC with high-permittivity cylinders.

Dual‐mode bandpass substrate integrated waveguide filter with a complementary split ring resonator

AbstractWe present a new bandpass filter by combining an isosceles right‐triangle substrate integrated waveguide (SIW) cavity with a complementary split ring resonator (CSRR) together. The first and second modes of the SIW cavity are used to form a desirable passband with the help of a perturbation metallic via‐hole. We introduce a CSRR at the ground plate of the SIW cavity to produce two controllable transmission zeros at the upper stopband, which improve the upper stopband characteristic greatly. Moreover, at the lower stopband, we make use of a pair of T‐shape stub‐loaded resonators to generate a transmission zero, and thus improve the out‐of‐band rejection greatly. To validate our design scheme, a filter sample has been fabricated and measured. The measured results and simulation ones are in good agreements. The filters show advantages of compactness, sharp stopband rejection, high frequency‐selectivity, and controllable passband and transmission zeros.

CPW-Fed UWB antenna with sharp and high rejection multiple notched bands using stub loaded meander line resonator

This paper presents a CPW-fed UWB filter-antenna with sharp and high rejection multiple band notches for band-notched UWB communication applications. The band notch operation is achieved by employing a sharp bandstop filter (BSF) with multiple reject bands using only one element meander line resonator at the bottom layer through theoretical calculations and parametric studies. The adjustment of the notched bands is successfully accomplished by loading the meander line with open ended stubs to modify the harmonic frequencies to the desired bands. The structure of the proposed BSF is simple and compact so that the proposed filter-antenna is achieved with the same size of the reference UWB antenna without an extra area. Measurement results show that the proposed filter-antenna has two notches at the WiMAX systems operating in the 5.8GHz (5.725–5.85GHz) and at the international telecommunication union (ITU) operating in the 8.2GHz (8.025–8.4GHz). Also, it has sharp rejection characteristics at the edges of the federal communication commission (FCC) band for UWB communications. The experimental measurements are in good agreement with theoretical and simulation results for the BSF and the filter-antenna. Moreover, the filter-antenna exhibits stable omnidirectional radiation patterns except at the notched bands.

Compact Liquid Crystal Based Tunable Band-Stop Filter with an Ultra-Wide Stopband by Using Wave Interference Technique

A wave interference filtering section that consists of three stubs of different lengths, each with an individual stopband of its own central frequency, is reported here for the design of band-stop filters (BSFs) with ultra-wide and sharp stopbands as well as large attenuation characteristics. The superposition of the individual stopbands provides the coverage over an ultra-wide frequency range. Equations and guidelines are presented for the application of a new wave interference technique to adjust the rejection level and width of its stopband. Based on that, an electrically tunable ultra-wide stopband BSF using a liquid crystal (LC) material for ultra-wideband (UWB) applications is designed. Careful treatment of the bent stubs, including impedance matching of the main microstrip line and bent stubs together with that of the SMA connectors and impedance adaptors, was carried out for the compactness and minimum insertion and reflection losses. The experimental results of the fabricated device agree very well with that of the simulation. The centre rejection frequency as measured can be tuned between 4.434 and 4.814 GHz when a biased voltage of 0–20 Vrms is used. The 3 dB and 25 dB stopband bandwidths were 4.86 GHz and 2.51 GHz, respectively, which are larger than that of other recently reported LC based tunable BSFs.

Optimisation of SIW bandpass filter with wide and sharp stopband using space mapping

ABSTRACTThis work presents a substrate integrated waveguide (SIW) bandpass filter with wide and precipitous stopband, which is different from filters with a direct input/output coupling structure. Higher modes in the SIW cavities are used to generate the finite transmission zeros for improved stopband performance. The design of SIW filters requires full wave electromagnetic simulation and extensive optimisation. If a full wave solver is used for optimisation, the design process is very time consuming. The space mapping (SM) approach has been called upon to alleviate this problem. In this case, the coarse model is optimised using an equivalent circuit model-based representation of the structure for fast computations. On the other hand, the verification of the design is completed with an accurate fine model full wave simulation. A fourth-order filter with a passband of 12.0–12.5 GHz is fabricated on a single layer Rogers RT/Duroid 5880 substrate. The return loss is better than 17.4 dB in the passband and the rejection is more than 40 dB in the stopband. The stopband is from 2 to 11 GHz and 13.5 to 17.3 GHz, demonstrating a wide bandwidth performance.

Microstrip bandpass filter design using split‐path method and optimized curvature corrections

SummaryBandpass filters with wide pass‐band are an essential requirement in various equipments of satellite and defence communication sectors. Here a method of split‐path interactions is proposed to approximately predict the resonant frequency and topology of bandpass filters which otherwise fall under the category of heuristic designs. Curved transmission lines are often required to make filter structures physically compact; however, curvature effects create errors in the theoretical (design) prediction of resonant or central frequencies for bandpass filter design. Earlier propositions on curvature corrections had been considerably precise, but recent design standards demand even higher accuracies. The prime feature of this work is the use of a meta‐heuristic optimization (i.e. Particle Swarm Optimization) technique in curvature corrections for the first time which brings accuracies of over 99% in the corrected results. The split paths used in this design are suitably curved, with the proposed optimized curvature correction technique, so as to attain a compact size of the filter. The resulting filter has a low insertion loss of around −1.00 dB and a sharp stopband cut‐off. Fabrication was done on a FR4 microstrip substrate with a good agreement between measured and simulated results. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Negative coupling and coupling phase dispersion in a silicon quadrupole micro-racetrack resonator.

We report the first experimental study of the effects of coupling phase dispersion on the spectral response of a two-dimensionally coupled quadrupole micro-racetrack resonator. Negative coupling in the system is observed to manifest itself in the sharp stop band transition and deep extinction in the pseudo-elliptic filter response of the quadrupole. The results demonstrate the feasibility of realizing advanced silicon microring devices based on the 2D coupling topology with general complex coupling coefficients.

Tooth-shaped plasmonic filter based on graphene nanoribbon

A class of single tooth-shaped plasmonic filter based on graphene nanoribbon is proposed in this paper, and the structure is numerically analysed by using finite-difference time-domain method. The tooth-shaped structure of graphene nanoribbon can induce a sharp band-stop effect in the transmission spectrum, and the filtering characteristics can be analysed by the scattering matrix method. The effective refractive index of the plasmonic waveguide mode in the graphene nanoribbon is analysed numerically, and it is found that the effective refractive index is influenced by both the chemical potential and the width of the nanoribbon, and when the width is narrower than 30 nm, the higher order mode disappears and the ribbon becomes a single mode waveguide. According to the scattering matrix method, the central frequencies of the transmission dips can be changed by changing the length and the width of the tooth. Flexible electrical tunability of this kind of filter by tiny change of the chemical potential of the graphene through electrical gating is also validated. In addition, transmission spectrum of multi-teeth shaped plasmonic filter is also studied. This kind of structure can possess the broad band-stop filtering property. The influences of tooth number and tooth period on transmission spectrum are investigated. We find that the transmission value can be reduced down to almost zero by adjusting the number of the teeth, also the tooth period can influence the central frequency of the stop band because of the coupling effects between each other. Like the single-tooth filter based on graphene nanoribbon, the multi-tooth broad band-stop filter can also be flexibly tuned by the geometric parameters of the structure and the chemical potential of the graphene. This work provides an effective method of designing graphene based ultra-compact tunable devices, and has extensive potential for designing all-optical integrated architectures for optical networks, communication and computing devices.

High-Sensitivity CMOS Super-Regenerative Receiver with Quench-Controlled High-&lt;formula formulatype="inline"&gt;&lt;tex Notation="TeX"&gt;$Q$&lt;/tex&gt; &lt;/formula&gt; Metamaterial Resonator for Millimeter-Wave Imaging at 96 and 135 GHz

High-sensitivity super-regenerative receivers (SRXs) are demonstrated at 96 and 135 GHz, respectively, in this paper. They are based on high-Q quench-controlled metamaterial resonators with a differential transmission line loaded with a split-ring resonator (DTL-SRR) and a differential transmission line loaded with a complementary split-ring resonator (DTL-CSRR) in 65-nm CMOS. High-Q oscillatory amplifications are established by the sharp stopband introduced by metamaterial resonators. As such, high detection sensitivity is achieved for SRXs at millimeter-wave regions. The fabricated 96-GHz DTL-CSRR-based SRX has a compact core chip area of 0.014 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> with measured power consumption of 2.8 mW, sensitivity of -79 dBm, noise figure (NF) of 8.5 dB, and noise equivalent power (NEP) of 0.67 fW/√(Hz). The fabricated 135-GHz DTL-SRR-based SRX has a compact core chip area of 0.0085 mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> with measured power consumption of 6.2 mW, sensitivity of -76.8 dBm, NF of 9.7 dB, and NEP of 0.9 fW/√(Hz). Compared to the conventional SRX with an LC-tank-based resonator at similar frequencies, the proposed SRXs have 2.8~4 dB sensitivity improvement and 60% smaller area. The integrated SRXs are also demonstrated for the imaging applications.

A novel microstrip lowpass filter with sharp roll-off and ultra-wide stopband using SICMRC

This paper presents a novel microstrip lowpass filter with sharp roll-off and ultra-wide stopband using stepped-impedance resonator and bended transmission line structure. The filter includes stepped-impedance prototype filter and stepped-impedance compact microstrip resonator cells that are combined in one structure. The proposed filter has good specifications such as sharp roll-off, ultra-wide stopband and low insertion loss. The transition band is approximately 0.25 GHz from 1.75 to 2 GHz with corresponding attenuation levels of −3 and −40 dB. The attenuation level in the stopband is better than −20 dB that is achieved from 1.94 to 23 GHz, and the insertion loss in the passband is less than 0.4 dB. The proposed filter is fabricated and measured, and the simulation and measurement results are found to be in good agreement with each other.

Radiation-rejection band inserted dual-band antenna using a split ring resonator for beyond 4G applications

We propose a very simple but effective method to switch a single-band antenna into a dual-band antenna by inserting a narrow radiation-prohibited band in the middle of the single pass band. To insert the radiation-rejection band, we intentionally induce strong resonance on a metamaterial-motivated split ring resonator (SRR) by placing it near a signal feeding transmission line of a proximity-coupled microstrip patch antenna, which blocks out flow of electromagnetic waves through the line. To maximize the blockage, we cut the SRR into a quadrangular loop that is exactly interlocked with the two sides of the right-angled microstrip line. Consequently, we show that we can split one pass band into two separated pass bands with an inserted sharp stop band in-between. Good agreements between the prediction and the measurement prove the validness of our approach. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:961–965, 2014