Filter Bandwidth Research Articles

High-Order Wideband Band-Pass Miniaturized Frequency-Selective Surface with Enhanced Equivalent Inductance

To extend the wideband performance of high-order band-pass filtering applications, optimized designs with knitted structures based on traditional miniaturized frequency-selective surfaces (FSSs) are proposed in this paper. The presented miniaturized FSSs consist of multiple metallic capacitive layers, knitted inductive layers, and substrates. In contrast to the conventional high-order miniaturized FSSs composed of metallic frames, patches, and substrates, the optimized miniaturized FSSs replace the original metallic wire frames with knitted structures. Both proposed modified miniaturized FSSs achieve a flat pass-band from 5.5 GHz to 10.3 GHz with a 3 dB bandwidth of 71.6% under vertical incidence. The unit cells have dimensions of 0.16 λ0 × 0.16 λ0 × 0.284 λ0 and 0.16 λ0 × 0.16 λ0 × 0.279 λ0, respectively, where λ0 is the free space wavelength at 7.9 GHz, which is the center frequency of the operating band. Numerical simulations and measurements demonstrate that the proposed modified miniaturized FSSs exhibit excellent wideband performance with clean transition bands around the pass-band during oblique incidence and are suitable for applications such as radomes, where wideband filtering is essential for covering multi-band functions of radar or communication instruments.

A Design Method and Application of Meta-Surface-Based Arbitrary Passband Filter for Terahertz Communication.

A meta-surface-based arbitrary bandwidth filter realization method for terahertz (THz) future communications is presented. The approach involves integrating a meta-surface-based bandstop filter into an ultra-wideband (UWB) bandpass filter and adjusting the operating frequency range of the meta-surface bandstop filter to realize the design of arbitrary bandwidth filters. It effectively addresses the complexity of designing traditional arbitrary bandwidth filters and the challenges in achieving impedance matching. To underscore its practicality, the paper employs silicon substrate integrated gap waveguide (SSIGW) and this method to craft a THz filter. To begin, design equations for electromagnetic band gap (EBG) structures were developed in accordance with the requirements of through-silicon via (TSV) and applied to the design of the SSIGW. Subsequently, this article employs equivalent transmission line models and equivalent circuits to conduct theoretical analyses for both the UWB passband and the meta-surface stopband portions. The proposed THz filter boasts a center frequency of 0.151 THz, a relative bandwidth of 6.9%, insertion loss below 0.68 dB, and stopbands exceeding 20 GHz in both upper and lower ranges. The in-band group delay is 0.119 ± 0.048 ns. Compared to reported THz filters, the SSIGW filter boasts advantages such as low loss and minimal delay, making it even more suitable for future wireless communication.

Multispectral Narrowband Frustrated Total Internal Reflection Filter with Inclusions of Plasmonic Nanoparticles

A spatial-frequency thin-film filter with inclusions of nanoparticles operating in the visible range of the spectrum is investigated. The effect of nanoparticles embedded in the central and lateral layers of the frustrated total internal reflection filter on the spectral characteristics, considering the frequency dispersion, is investigated. It is shown that plasmonic effects cause the splitting of the filter bandwidth into a set of narrow-band spectral lines and the angular splitting of the incident beam into a set of output beams. It is demonstrated that due to the difference in the resonance conditions for s- and p-polarization waves, the spectral lines of transparency do not coincide, which indicates the possibility of using the filter as a polarizer.

Chebyshev filter and Butterworth filters: Comparison and applications in different cases

This study focuses on the filter selection problem in signal processing and wireless communication applications. Specifically, addressed two different filter selection problems: the Chebyshev filter and the Butterworth filter. Using MATLAB, in order to design and model these two types of filters. The performance, frequency response, transition band width, filter order, design complexity and target application of Chebyshev filter and Butterworth filter under different parameters are analyzed and compared. The selection of the two filters under different conditions and the reasons for choosing them are discussed. The Chebyshev filter is suited for applications that call for a high frequency response, and Chebyshev filters provide a steeper roll-down slope, which can suppress high-frequency noise and interference signals, according to the test results, it is widely used in communication systems. On the other hand, the Butterworth filter is more suitable for applications that require a flat passband and a wide stopband, such as audio systems.

Design of efficient, reliable, and wide-band filter electrochemical capacitors via matching positive with negative electrodes

Design of efficient, reliable, and wide-band filter electrochemical capacitors via matching positive with negative electrodes

Investigating the Performance of Gammatone Filters and Their Applicability to Design Cochlear Implant Processing System

Commercially available cochlear implants are designed to aid profoundly deaf people in understanding speech and environmental sounds. A typical cochlear implant uses a bank of bandpass filters to decompose an audio signal into a set of dynamic signals. These filters’ critical center frequencies f0 imitate the human cochlea’s vibration patterns caused by audio signals. Gammatone filters (GTFs), with two unique characteristics: (a) an appropriate “pseudo resonant” frequency transfer function, mimicking the human cochlea, and (b) realizing efficient hardware implementation, could demonstrate them as unique candidates for cochlear implant design. Although GTFs have recently attracted considerable attention from researchers, a comprehensive exposition of GTFs is still absent in the literature. This paper starts by enumerating the impulse response of GTFs. Then, the magnitude spectrum, |H(f)|, and bandwidth, more specifically, the equivalent rectangular bandwidth (ERB) of GTFs, are derived. The simulation results suggested that optimally chosen filter parameters, e.g., critical center frequencies,f0; temporal decay parameter, b; and order of the filter, n, can minimize the interference of the filter bank frequencies and very likely model the filter bandwidth (ERB), independent of f0b. Finally, these optimized filters are applied to delineate a filter bank for a cochlear implant design based on the Clarion processor model.

The Influence of Spectral Filtering Bandwidth and Laser Gain on the Bound-State Pulse Formation Mechanism and Evolutionary Dynamics in the All-Fiber Mamyshev Oscillator

We present a numerical investigation of the bound-state pulse formation mechanism and evolutionary dynamics based on the pump strength and spectral filtering bandwidth in the all-fiber Mamyshev oscillator. Through the numerical simulation and analysis, the different mode-locked pulses’ (such as single pulses, bound-state pulses, and chaotic multi-pulses) regime transformation conditions are quantified. The results suggest that with an increase in the pump strength, the sub-pulse energy and output coupler of the Mamyshev oscillator show an inverse proportion trend, which plays an important role in increasing the number of sub-pulses in the bound-state pulses’ state. Furthermore, optimization schemes, such as adjusting the filter bandwidth and slowing down the accumulation of nonlinear effects, are proposed to achieve a high-energy pulse output in the Mamyshev oscillator.

A New Compact Wideband Filter Based on a Coupled Stepped Impedance Resonator.

A new compact wideband filter is introduced to address the requirements of recent communication and radar systems. The filter is based on a quarter-wavelength short-circuit coupled stepped impedance resonator (SIR). The analytical solution shows that the suggested SIR resonator provides a compact size and a wide stopband response, which are essential features in many wireless communication systems. The analytical results also reveal that increasing the impedance ratio of the SIR extends the stopband by increasing the first spurious response and reducing its total length. A compact two-coupled short-circuit SIR filter is designed at 1.23 GHz. The design approach is validated using an ideal transmission line modeling analysis and electromagnetic simulation using CST Microwave Studio 2021. The proposed structure is shown to be flexible, allowing the achievement of a relative bandwidth as low as 5% and as high as 50%. A four-resonator filter is designed by cascading two stages of the designed two-coupled short-circuit SIR filter, which are coupled through a quarter-wavelength line. The simulation results illustrate that the suggested structure can be used to design a filter with any number of resonators. The filter is implemented using a high-resolution LPKF laser machine on Rogers RT/duroid 6010.2LM material with a thickness of 0.635 mm. From the measurements, the bandwidth is found to be 390 MHz and centered at 1325 MHz (29.4% relative bandwidth) and the insertion loss is 1.3 dB. The simulation and experimental results verify the proposed approach and indicate the potential of this component in meeting the design requirements of next-generation microwave circuits related to flexibility and size-compactness.

Measurements of particle extinction coefficients at 1064 nm with lidar: temperature dependence of rotational Raman channels.

Aerosol intensive optical properties, including lidar ratio and particle depolarization ratio, are of vital importance for aerosol typing. However, aerosol intensive optical properties at near-infrared wavelength are less exploited by atmospheric lidar measurements, because of the comparably small backscatter cross section of Raman-scattering and a low efficiency of signal detection compared to what is commonly available at 355 nm and 532 nm. To obtain accurate optical properties of aerosols at near-infrared wavelength, we considered three factors: Raman-spectra selection, detector selection, and interference-filter optimization. Rotational Raman scattering has been chosen for Raman signal detection, because of the higher cross-section compared to vibrational Raman scattering. The optimization of the properties of the interference filter are based on a comprehensive consideration of both signal-to-noise ratio and temperature dependence of the simulated lidar signals. The interference filter that has eventually been chosen uses the central wavelength at 1056 nm and a filter bandwidth (full-width-at-half-maximum) of 6 nm. We built a 3-channel 1064-nm rotational Raman lidar. In this paper two methods are proposed to test the temperature dependence of the signal-detection unit and to evaluate the quality of the Raman signals. We performed two measurements to test the quality of the detection channel: cirrus clouds in the free troposphere and aerosols in the planetary boundary layer. Our analysis of the measured Raman signals shows a negligible temperature dependence of the Raman signals in our system. For cirrus measurements, the Raman signal profile did not show crosstalk even for the case of strong elastic backscatter from clouds, which was about 100 times larger than Rayleigh scattering in the case considered here. The cirrus-mean extinction-to-backscatter ratio (lidar ratio) was 27.8 ± 10.0 sr (1064 nm) at a height of 10.5-11.5 km above ground. For the aerosols in the planetary boundary layer, we found the mean lidar ratio of 38.9 ± 7.0 sr at a height of 1.0-3.0 km above ground.

An efficient equalization filter design approach for the accurate sound reproduction in a room environment with wide-band content

In some sound reproduction applications, a desired sound field needs to be reproduced by remote loudspeakers in a room with sufficient accuracy over a wide frequency band. When low-frequency room modes exist and the low-frequency content is required to be reproduced accurately, an equalization filter with a long time-domain response may be necessary, resulting in a filter with a significantly high filter order, especially when the sampling rate is high for the high-frequency content. This imposes computational challenges on both filter design and implementation. In this article, a convex formulation is proposed for the wide-band sound reproduction filter design. To address issues due to the low-frequency room modes, a reduced-order technique is then proposed based on a sub-band filter structure where a low sampling rate is used to equalize the low-frequency room mode characteristics, and a high sampling rate is used for high-frequency features which usually has a short time span in response. The computational time can be reduced by several orders of magnitude and the numerical stability can be improved when the proposed order reduction method is used to eliminate redundant orders. Simulation and experimental results confirm the accuracy and efficiency advantages of the proposed method.

Temperature Effect Separation of Structure Responses from Monitoring Data Using an Adaptive Bandwidth Filter Algorithm.

Temperature is one of the most important factors significantly affecting damage detection performance in civil engineering. A new method called the Adaptive Bandwidth Filter Algorithm (ABFA) is proposed in this paper to separate the temperature effect from quasi-static long-term structural health monitoring data. The Adaptive Bandwidth Filter Algorithm (ABFA) is referred to as an algorithm of automatically adjusting the frequency bandwidth filter via the particle swarm optimization (PSO) algorithm. Considering the obvious multi-scale feature of the collected data of civil structure, the acquired time series are divided into different time scales (for example, day, month, year, etc.), and these scales in the frequency domain correspond to the center frequencies of the adaptive bandwidth filter. The temperature effect on structure responses across different time scales is thereafter explored by adaptively adjusting the frequency bandwidth of the filter based on the known center frequencies of different scales. The relationship between the temperature and the structure responses is established through statistical regression facilitated by sufficient in situ monitoring data. Simulation and experiment results show the very promising performance of the proposed algorithm and decouple the temperature effect accurately from the contaminated data; thus an enhanced capability of damage detection is achieved.

Compact and wideband nanoacoustic pass-band filters for future 5G and 6G cellular radios

Over recent years, the surge in mobile communication has deepened global connectivity. With escalating demands for faster data rates, the push for higher carrier frequencies intensifies. The 7–20 GHz range, located between the 5G sub-6 GHz and the mm-wave spectra, provides an excellent trade-off between network capacity and coverage, and constitutes a yet-to-be-explored range for 5G and 6G applications. This work proposes a technological platform able to deliver CMOS-compatible, on-chip multi-frequency, low-loss, wide-band, and compact filters for cellular radios operating in this range by leveraging the micro-to-nano scaling of acoustic electromechanical resonators. The results showcase the first-ever demonstrated low insertion loss bank of 7 nanoacoustic passband filters in the X-band. Most of the filters showcase fractional bandwidths above 3% and sub-dB loss per stage in an extremely compact form factor, enabling the manufacturing of filters and duplexers for the next generation of mobile handsets operating in the X-band and beyond.

A systematic approach for the development of wide band band pass filters using resonators

In this paper, for the first time a novel and systematic approach is presented to construct a wideband Band Pass Filters (BPFs) with high selectivity and stopband response. Two BPFs (Filter I and Filter II) were built on a Taconic (TLX-9) substrate using semi-circular tapered coupled lines, Defected Microstrip Structures (DMSs), Defected Ground Structures (DGS), and Stepped Impedance Resonators (SIRs). The precision of the design procedure is confirmed through 3-D full wave Electro-Magnetic (EM) simulation software where two wideband filters were designed for L, S, and C-bands. Additionally, parametric analysis has been done to evaluate the performance of both wideband filters with key features such as return loss, insertion loss, Band Width (BW), selectivity, and stopband response. Even-odd mode analysis has been implemented using the ABCD matrix that acts as a source for mathematical analysis of Filter I. Eventually, two wideband filters have been fabricated and tested for their effectiveness, and the measured results of two wideband filters are in line with the simulated ones with slight deviations due to fabrication tolerances and connector losses. The prototyped Filter I functions as a bandpass in the frequency range of 2.4 GHz to 4.8 GHz with a maximum insertion loss of 0.85 dB and return loss of 19.5 dB thereby providing 64% Fractional Band Width (FBW). Near 19 dB rejection is observed in the lower and upper stopband regions with BW (stopbands) greater than 2 GHz. Moreover, Filter II is also fabricated and tested. The experimental return loss of 20 dB and insertion loss (maximum) of 0.73 dB over the passband (1.9 GHz to 3.4 GHz) were found with 0.7 Selectivity Factor (SF). More than 20 dB attenuation of stopbands (lower and upper) was achieved. Thus, the fabricated wideband BPFs operate in L, S, and C-bands for radars, satellite and long-distance radio communications, and military telemetry applications.

Flexible Film Bulk Acoustic Wave Filter Based on Poly(vinylidene fluoride-trifluorethylene).

Poly(vinylidene fluoride-trifluorethylene) (P(VDF-TrFE)) has promising potential applications in radio-frequency filters due to their excellent piezoelectric properties, flexibility, and stability. In this paper, a flexible film bulk acoustic wave filter is investigated based on P(VDF-TrFE) as piezoelectric film. A new method based on three-step annealing is developed to efficiently remove the porosity inside the P(VDF-TrFE) films so as to improve its properties. The obtained film achieved high β-phase content beyond 80% and a high piezoelectric coefficient of 27.75 pm/V. Based on the low porosity β-phase films, a flexible wide-band RF filter is designed, which consists of a bulk acoustic wave resonator and lumped inductor-capacitor elements as a hybrid configuration. The resonator sets the filter's center frequency, while the lumped LC-based matching network extends the bandwidth and enhances out-of-band rejection. The testing results of the proposed wide-band filter show its good performance, with 12.5% fractional bandwidth and an insertion loss of 3.1 dB. To verify the possibility of folding and stacking the flexible bulk acoustic wave devices for high-density multi-filter integration in MIMO communication, bending tests of the filter are also conducted with the bending strain range up to 5500 με. The testing results show no noticeable performance degradation after four bending cycles. This work demonstrates the potential of β-phase P(VDF-TrFE) bulk acoustic wave filters to expand the scope of future flexible radio-frequency filter applications.

A Monolayer Frequency‐Selective Surface for Wideband Shielding Application with Adequate Out‐of‐Band Separation and Angular Stability

In the proposed paper, a monolayer band‐stop frequency‐selective surface (FSS) is structured and analyzed for application in wideband shielding. The paper proposes an organized step‐by‐step method to design the frequency‐selective surface (FSS) to achieve enhanced shielding effectiveness (SE) over the entire band. The suggested FSS comprises of tripole‐shaped unit cells on both sides of a monolayer FR‐4 substrate to offer adequate shielding over the band of 3.2–8.82 GHz which includes both C‐ and X‐bands. The operating band of the FSS achieves ultrawideband shielding by means of 93% bandwidth with 60–100 dB shielding effectiveness. Experimental data are employed for the characteristics that are fairly well congruent to simulated results. Higher angular stability beyond 80° characterizes the proposed FSS. A wide range of potential uses for the proposed design exists, including microwave shielding, wideband filtering, as well as radar cross‐section (RCS) reduction, among others. The out‐of‐band RCS reduction capability of the FSS is also investigated and presented in this paper.

A miniaturized ultra-wideband filter with high rejection and selectivity based on dual-notch bands.

A novel compact and highly selective Ultra Wide Band (UWB) filter is proposed using multimode resonator (MMR) technology. To begin with, the filter's ultra-wideband performance is achieved by coupling a stepped-triangular multimode resonator with input-output feedlines. Furthermore, dual-notch band characteristics are realized at 6.80 GHz and 9.82 GHz, employing asymmetric coupled lines and the split ring resonator (SRR) methods. Eventually, by using a Defected Ground Structure (DGS), the filter's correct transmission zero is deepened, further enhancing the out-of-band suppression performance at higher frequencies. The measured results are in excellent agreement with the experimental results, and the filter has a passband range of 3.52-11.68 GHz, a center frequency of 7.59 GHz, an insertion loss of just 0.61 dB, and a return loss of more than 18 dB. The transmission zeros have a rejection capability of more than 47 dB attenuation, and the rectangular coefficient of the filter is 1.34, which is outstanding for filtering out the interference signals in the parasitic passband with superior selectivity. The overall structure is compact, and the size is just 0.41λg×0.20λg. The filter can be used for UWB system filtering and also to avoid interference from some Wireless Local Area Network (WLAN) IEEE 802.11 series and x-band satellite link frequency bands.

Identification of the Bandwidth of a Magneto-Inertial Navigation Filter

We address the analysis of a nonlinear navigation filter used in Magneto-Inertial Dead-Reckoning (MIDR) whose input data are provided by a home-made device. This filter takes the measurements given by the magnetic sensors as inputs and returns the velocity of the body. Therefore, any unmodeled time-varying disturbance in the measurements impacts the estimation of the velocity and yields errors that distort the estimation. For dimensioning purpose, we aim to identify the bandwidth of the linearized part of this filter. To derive a model of this bandwidth, we first simplify our filter as a time-invariant Single-Input Single-Ouput (SISO) system in the situation where the steady-state regime is reached. The Best Linear Approximation (BLA) of this nonlinear system can hence be described by a conventional transfer function. We justify the validity of such a linear approximation for Extended Kalman Filters (EKF) and identify it with different methods, yielding a model for the bandwidth depending on the experimental conditions of navigation. We show that our filter is actually suitable for pedestrian navigation. Finally, simulations in realistic physical situations are used for validation.

Hetero Acoustic Layer Surface Acoustic Wave Resonator Composed of LiNbO3 and Quartz.

In this work, a shear-horizontal (SH) mode surface acoustic wave (SAW) resonator based on LiNbO3 (LN)/Quartz (Qz) hetero acoustic layer (HAL) structure was studied by simulation and experiment. By this HAL structure, the displacement and electric displacement are well confined in the piezoelectric layer. A lower mechanical loss of Qz than that of lossy amorphous SiO2 further enhances the quality ( Q ) factor. In addition, a negative temperature coefficient of frequency (TCF) of LN is compensated by selecting the crystalline orientation of Qz with a positive TCF. According to simulation results, the Euler angles of (0°, 101°, and 0°) and the normalized thickness of 0.2-0.3 λ (wavelength) for LN are selected to obtain a higher impedance ratio ( Z -ratio) and bandwidth (BW). The Euler angles of (0°, 160°, and 90°) for Qz are selected to obtain the positive maximum TCF. The fabricated resonator exhibits a Z -ratio of 95 dB and a BW of 15.9% in the 700 MHz range. The fit figure of merit (FoM) reaches 410, which is the best level ever reported for an LN-based resonator. The TCF of the resonator is -77 ppm/°C at anti-resonance frequency. A group of resonators composed of LN and LN/Qz with thin and thick electrodes were fabricated to further illustrate the good performance of LN/Qz. The LN/Qz HAL SAW resonator demonstrated in this work exhibits a high Z -ratio, low TCF, and wideband, which has the potential for high-performance wideband filters with steep passband and good temperature characteristics.

Miniaturised wideband bandpass filter with good selectivity based on 3D heterogeneous integrated passive device technology

AbstractThe miniaturised wideband filter with good frequency selectivity and wide stopband is proposed, which is based on three‐dimensional (3D) heterogeneous integrated passive device technology. The proposed sixth‐order wideband bandpass filter is based on the magnetic‐coupling‐loaded highpass‐lowpass lumped topology and implemented by the 3D heterogeneous integration process, integrating GaAs‐based and Glass‐based micro‐nano‐scale processes together. Then, lumped inductors are designed in the Glass substrate with low dielectric loss tangent and realised by a three‐dimensional spiral structure. Therefore, the inductors have high quality factors and small sizes. The lumped capacitors are designed using the GaAs thin film process. Finally, a prototype with a 3‐dB fractional bandwidth of 42% is designed and fabricated at 3.875 GHz (f0). The upper‐stopband attenuation higher than 30 dB is extended to more than 5.15f0. It occupies only 0.014 × 0.018 λ02 (1.1 × 1.42 mm2), where λ0 is the free‐space wavelength at f0.

Narrow-bandwidth picosecond dissipative soliton resonance in an all-anomalous-dispersion Er/Yb co-doped fiber laser

First, it is numerically demonstrated that narrow-bandwidth picosecond dissipative soliton resonance (DSR) pulses can be obtained in the all-anomalous-dispersion Er/Yb co-doped fiber (EYDF) laser, which is based on the nonlinear polarization rotation (NPR) mode-locking and narrow-band spectral filtering. The generated DSR pulses are characterized by a central peak on top of a rectangular pedestal temporally and two high-intensity spectral sidebands with less than 0.6-nm bandwidth. Second, the impacts of several key cavity parameters on characteristics of DSR pulses are investigated. Particularly, a new phenomenon of periodic evolution of the DSR pulse, featuring alternated high and low peak powers with the round-trips, is discovered by tuning filter bandwidth or net-cavity dispersion. Multi-pulse dissipative soliton (DS) and noise-like pulse (NLP) are also observed in the fiber laser. Finally, a 22.3-ps DSR pulse with 287.5-W peak power can be further compressed to 4.3 ps with 1126.5-W peak power by the dispersion compensation. This work further enriches the DSR pulse dynamics in the anomalous-dispersion region and paves a way to realize narrow-bandwidth picosecond DSR pulse fiber lasers.