Filter Bandwidth Research Articles

Interdigital Resonators in Wideband Ridged-Waveguide Filters

Abstract. An interdigital resonator approach for wideband filter applications in ridged-waveguide technology is presented. The interdigital arrangement of the ridged-waveguide resonators ensures stronger coupling between the resonators. As the coupling sections are consequently enlarged by the interdigital arrangement of the resonators, more feasible filter structures are possible at increasing frequencies. The approach itself can be easily implemented with conventional filter synthesis formulas, which is demonstrated by two 20 GHz examples with a bandwidth of 2 GHz and 100 MHz, respectively. The designed filters are subsequently compared to the standard implementation of ridged-waveguide filters.

Low-Power, Reconfigurable Brillouin RF Photonic Bandstop Filters

Stimulated Brillouin Scattering (SBS) has been widely used to realize narrowband as well as wideband microwave photonic bandstop filters. However, most Brillouin based wide-band bandstop filters require large powers and have high complexity. In this letter, we propose a novel approach to realize a wideband, reconfigurable and tunable Brillouin-based microwave photonic bandstop filter using RF phase engineering. We demonstrate bandstop filters with suppression of >15 dB for moderate bandwidths and maximum bandwidth reconfigurability up to 1 GHz by using two pumps with powers of 8.2 dBm and 9.3 dBm. Further, we also demonstrate switching from a bandpass to a bandstop filter with simple phase manipulations. This letter presents numerical simulations, analysis, and experimental results for the proposed filter. Compared to conventional Brillouin systems, the proposed filter is extremely power-efficient.

Signal-to-Noise Ratio Analysis for the Voltage-Mode Read-Out of Quartz Tuning Forks in QEPAS Applications

Quartz tuning forks (QTFs) are employed as sensitive elements for gas sensing applications implementing quartz-enhanced photoacoustic spectroscopy. Therefore, proper design of the QTF read-out electronics is required to optimize the signal-to-noise ratio (SNR), and in turn, the minimum detection limit of the gas concentration. In this work, we present a theoretical study of the SNR trend in a voltage-mode read-out of QTFs, mainly focusing on the effects of (i) the noise contributions of both the QTF-equivalent resistor and the input bias resistor RL of the preamplifier, (ii) the operating frequency, and (iii) the bandwidth (BW) of the lock-in amplifier low-pass filter. A MATLAB model for the main noise contributions was retrieved and then validated by means of SPICE simulations. When the bandwidth of the lock-in filter is sufficiently narrow (BW = 0.5 Hz), the SNR values do not strongly depend on both the operating frequency and RL values. On the other hand, when a wider low-pass filter bandwidth is employed (BW = 5 Hz), a sharp SNR peak close to the QTF parallel-resonant frequency is found for large values of RL (RL > 2 MΩ), whereas for small values of RL (RL < 2 MΩ), the SNR exhibits a peak around the QTF series-resonant frequency.

Investigation of a Tunable Microwave Photonic Filter Based on an Acetylene Reference Cell

Introduction.Recently, the development of tunable microwave photonic filters has attracted great scientific and practical interest. Such microwave photonic filters are a good alternative to traditional electrical solutions, due to low losses, wide operating frequency range and such filters can be easily integrated into various telecommunication systems. By using an acetylene reference cell and a laser with tunable wavelength can make it possible to create tunable microwave photonic filter with wide operating frequency range.Aim.Investigation of the characteristic of a tunable microwave photonic filter based on an acetylene reference cell, as well as research possible solution to reduce losses in filter bandwidth; numerical simulation of microwave photonic filter characteristics.Materials and methods.Experimental study was carried out on an experimental prototype of a tunable microwave photonic filter. The filter consisted of a laser with a tunable wavelength, a phase modulator, an acetylene reference cell, an optical fiber connecting the gas cell with a photodetector, and a photodetector. Theoretical study was carried out by modeling of the transmission characteristics of the microwave photonic filter.Results.Experimental transmission characteristics of a tunable microwave photonic filter were obtained. The tuning of the filter bandwidth by tuning laser wavelength was studied. Modeling of transmission characteristics of microwave photonic filter was performed. Possible solution to reduce losses in filter bandwidth was proposed.Conclusion.A tunable microwave photonic filter based on an acetylene reference cell is proposed. Losses in the filter bandwidth was about −30 dB. Using high-power laser and a photodetector with a high photocurrent can reduce losses in the filter bandwidth.

Detection of distributed and localized faults in rotating machines using periodically non-stationary covariance analysis of vibrations

The covariance structure for vibrations of the noising mechanism for a port crane and a wind turbine with gear tooth breakage are studied on the basis of their models in the form of periodically non-stationary random processes (PNRPs). The investigation is performed by the authors using PNRP statistical analysis methods. The estimations of the basic frequencies of the vibration’s deterministic components and the time changes of the power for the stochastic part (the PNRP variance) are the key issues of this analysis. In the present paper, the basic frequency estimators are obtained using the least squares technique which are characterized by the maximum of the signal-to-noise ratio as compared with techniques known in the literature. Using the basic frequency, values for the Fourier coefficients for the mean and covariance functions are calculated and the dependencies of the forenamed moment functions on time and lag are ascertained. The amplitude spectra of the deterministic oscillations and the time changes of the power of the stochastic part are presented. These spectra are considered as the symptomatic features of the mechanism’s state of health. It is revealed that the high-frequency modulation of PNRP carrier harmonics is narrow-band for both distributed and localized faults. Using bandpass filtering and Hilbert transform, the quadratures for each high-frequency component are separated and analyzed. It is shown that the auto- and cross-covariance structure of the high-frequency component quadratures characterizes the specific features of the different types of faults. Using the cross-covariance map for high-frequency components, the peculiarities of the bandpass filtering of vibrations for a damaged wind turbine’s gearbox as a PNRP’s is considered. It is shown that the filtering bandwidth cannot be narrower than 14 times the basic frequency. This bandwidth essentially exceeds that recommended in the literature (two to three times the basic frequency).

Fully Automatic In-Situ Reconfiguration of Optical Filters in a CMOS-Compatible Silicon Photonic Process

Automatic reconfiguration of optical filters is the key to novel flexible RF photonic receivers and Software Defined Radios (SDRs). Although silicon photonics (SiP) is a promising technology platform to realize such receivers, process variations and lack of in-situ tuning capability limit the adoption of SiP filters in widely-tunable RF photonic receivers. To address this issue, this work presents a first ‘in-situ’ automatic reconfiguration algorithm and demonstrates a software configurable integrated optical filter that can be reconfigured on-the-fly based on user specifications. The presented reconfiguration scheme avoids the use of expensive and bulky equipment such as an Optical Vector Network Analyzer (OVNA), does not use simulation data for reconfiguration, reduces the total number of thermo-optic tuning elements required, and eliminates several time-consuming configuration steps as in the prior art. This makes this filter ideal in a real-world scenario where the user specifies the filter center frequency, bandwidth, required rejection, and filter type (Butterworth, Chebyshev, etc.), and the filter is automatically configured regardless of process, voltage, and temperature (PVT) variations. We fabricated our design in AIM Photonics' Active SiP process and have demonstrated our reconfiguration algorithm for a second-order filter with a 3 dB bandwidth of 3 GHz, 2.2 dB insertion loss, and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$&gt;$</tex-math></inline-formula> 30 dB out-of-band rejection using only two reference laser wavelength settings. Since the filter photonic integrated circuit (PIC) is fabricated using a CMOS-compatible SiP foundry, the design is manufacturable with repeatable and scalable performance suited for its integration with electronics to realize complex chip-scale RF photonic systems.

Study of the Performance Enhancement of Sc-Doped AlN Super High Frequency Cross-Sectional Lamé Mode Resonators

The increasing use of mobile broadband requires new acoustic filtering technologies that can operate efficiently at frequencies above 6 GHz. Previous research has shown that AlN Super High Frequency (SHF) Cross-Sectional Lamé Mode resonators (CLMRs) can address this challenge, but their performance is limited by the piezoelectric strength of AlN. In this work, we explore the use of substitutional doping of Al in AlN with Sc to enhance the kt2 values of SHF CLMRs. Our results showed that the measured kt2·Qm product of Al72Sc28N CLMRs was four times greater than that of AlN CLMRs operating at the same frequency. Additionally, the measured fractional bandwidth (FWB) of Al72Sc28N 2nd order ladder filters was 4.13%, a fourfold improvement over AlN filters with the same design. We also discuss other aspects of the technology, such as power handling, losses, and spurious mode suppression, and identify potential areas for future research.

High-Q cascaded single-passband microwave photonic filter based on an optical-electrical feedback loop.

A cascaded microwave photonic filter refers to a microwave photonic filter (MPF) with higher performance obtained by cascading a MPF with two different structures. A high-Q cascaded single-passband MPF is proposed experimentally based on stimulated Brillouin scattering (SBS) and an optical-electrical feedback loop (OEFL). In this experiment, the pump light of SBS is provided by a tunable laser. The Brillouin gain spectrum generated by the pump light is used to amplify the phase modulation sideband, and the narrow linewidth OEFL is subsequently used to compress the passband width of the MPF. By carefully adjusting the pump wavelength and tuning the tunable optical delay line, stable tuning can be achieved for a cascaded single-passband MPF with a high-Q value. The results have demonstrated that the MPF has characteristics of high-frequency selectivity and a wide frequency tuning range. Meanwhile, the filtering bandwidth is up to 300kHz, the out-of-band suppression is more than 20dB, the maximum Q-value is 5.333×104, and the center frequency tuning range is 1-17GHz. The cascaded MPF proposed not only achieves a higher Q-value, but also has the advantages of tunability, a high out-of-band rejection ratio, and strong cascaded ability.

Wrinkle Detection in Carbon Fiber-Reinforced Polymers Using Linear Phase FIR-Filtered Ultrasonic Array Data

Carbon fiber-reinforced polymers (CFRP) are extensively used in aerospace applications. Out-of-plane wrinkles frequently occur in aerospace CFRP parts that are commonly large and complex. Wrinkles acting as failure initiators severely damage the mechanical performance of CFRP parts. Wrinkles have no significant acoustic impedance mismatch, reflecting weak echoes. The total focusing method (TFM) using weak reflection signals is vulnerable to noise, so our primary work is to design discrete-time filters to relieve the noise interference. Wrinkles in CFRP composites are geometric defects, and their direct detection requires high spatial precision. The TFM method is a time-domain delay-and-sum algorithm, and it requires that the time information of filtered signals has no change or can be corrected. A linear phase filter can avoid phase distortion, and its filtered signal can be corrected by shifting a constant time. We first propose a wrinkle detection method using linear phase FIR-filtered ultrasonic array data. Linear phase filters almost do not affect the wrinkle geometry of detection results and can relieve noise-induced dislocation. Four filters with different bandwidths have been designed and applied for wrinkle detection. The 2 MHz bandwidth filter is recommended as an optimum choice.

Large-tunable microwave photonics frequency multiplier overcoming the fixed filter bandwidth limitation on improved feed-forward modulation technology

Improved feed-forward modulation (IFFM) technology is a two-stage modulation photonics design that achieves coherent frequency up-conversion based on incoherent optical carriers. For the scheme, at least two optical fixed filters are required; the first is used to extract desired optical sidebands for the second-stage modulation’s driving signal generation, and the second filter is to suppress unwanted optical harmonics for high-quality heterodyne detection. This is for a fixed-frequency signal generation. To accommodate tunable frequency signal generation, at least two tunable optical filers are needed. In this paper, a wide frequency tunable method for an IFFM-based frequency multiplier with only a fixed bandwidth optical filter is proposed. A proof-of-concept experiment successfully demonstrates the tuning mechanism of the scheme. The scheme exploits the two pairs of coherent optical sidebands generated from two incoherent light sources to realize coherent addition of the two beat signals from each pair to attain a high-power frequency-multiplied signal for enhanced transmission power budget. From the simulation, a frequency multiplication factor of 16 and a 160-GHz signal with a stable frequency and a power level enhanced by 19 dB are achieved by employing two incoherent lasers. By adjusting the output frequency of the local oscillator, we show that multi-band signals generation, including microwave, millimeter- and terahertz-wave, can be realized, and the performance of the generated signals is also investigated.

Simulation and Performance Evaluation of Laser Heterodyne Spectrometer Based on CO2 Absorption Cell

The laser heterodyne radiometer (LHR) has the advantages of miniaturization, low cost, and high spectral-resolution as a ground-verification instrument for satellite observation of atmospheric trace-gas concentration. To verify the accuracy of LHR measurements, a new performance evaluation method is presented here, based on an ASE source and a CO2 absorption cell in the laboratory. Preliminary simulation analysis based on the system parameters of LHR is carried out for the performance analysis and data processing of this new combined test system. According to the simulation results, at wavelength deviation of fewer than 30 MHz, the retrieval error, which increases with bandwidth, can obtain an accuracy of 1 ppm within the bandwidth range of the photodetector (1.2 GHz) when this instrument line shape (ILS) is calibrated. Meanwhile, when the filter bandwidth is less than 200 MHz, the maximum error without ILS correction does not exceed 0.07 ppm. Moreover, with an ideal 60 MHz bandpass filter without ILS correction, LHR’s signal-to-noise ratio (SNR) should be greater than 20 to achieve retrieval results of less than 1 ppm. When the SNR is 100, the retrieval error is 0.206 and 0.265 ppm, corresponding to whether the system uncertainties (temperature and pressure) are considered. Considering all the error terms, the retrieval error (geometrically added) is 0.528 ppm at a spectral resolution of 0.004 cm−1, which meets the measurement accuracy requirement of 1 ppm. In the experiment, the retrieval and analysis of the heterodyne signals are performed for different XCO2 with [400 ppm, 420 ppm] in the absorption cell. Experimental results match well with the simulation, and confirm the accuracy of LHR with an error of less than 1 ppm with an SNR of 100. The LHR will be used to measure atmospheric-CO2 column concentrations in the future, and could be effective validation instruments on the ground for spaceborne CO2-sounding sensors.

High Selectivity, Dual-Mode Substrate Integrated Waveguide Cavity Bandpass Filter Loaded Using CCSRR

In this paper, a third-order, high selectivity Substrate Integrated Waveguide (SIW) bandpass filter (BPF) loaded with Circular Complementary Split-Ring Resonator (CCSRR) is proposed for C band applications. The SIW cavity BPF comprises two stepped resonators ([Formula: see text] and [Formula: see text]) and one CSRR ([Formula: see text]) engraved on the top metal plate. Initially, the cavity loaded with stepped resonators ([Formula: see text] and [Formula: see text]) alone does not make a good selectivity on the lower out of band. Hence, the CCSRR is introduced between the stepped resonators ([Formula: see text] and [Formula: see text]) to improve the filter’s selectivity and enhance the filter’s bandwidth. The introduction of CCSRR enhances the selectivity on the lower out-of-band at 5.5[Formula: see text]GHz, and the extra pole increases the bandwidth. The metamaterial behavior of CCSRR is validated by permittivity extraction. The 3[Formula: see text]dB bandwidth of the third-order SIW filter is 840 MHz with a center frequency of 6.18[Formula: see text]GHz. The designed filter uses RTDuroid 5880 substrate of [Formula: see text] = 2.2 with a size of 28.4 × 28.4 × 0.51[Formula: see text]mm3. The proposed filter measurement and simulated results agree with each other.

Robust tuning of uncertainty and disturbance estimator-based control for stable processes with time delay

To expand the potential of uncertainty and disturbance estimator (UDE)-based control in practical application to most industrial stable processes, this paper proposes a convenient yet robust tuning rule according to the widely used first-order plus time delay (FOPTD) plant. The Smith predictor is first introduced to anticipate the delay-free output, which guarantees signal synchronizations in three control modules and enables remarkable restorations of nominal stability and performance. Then a second-order filter is employed in UDE to decouple the trade-off between disturbance rejection and noise attenuation. Based on this improvement and fixing both tracking speed and feedback gain to suggested patterns, the exhaustive evaluations for robustness against model distortion are executed through scanning the dimensionless filter bandwidth. The boundary demarcation triggered by the plunge of the continuous range of tolerable mismatched delays subsequently facilitates the formulation of an intuitive tuning rule with prescribed robustness. Its inherent model-based scaling property largely enables this rule to be implemented readily in industrial processes just like the proportional-integral-derivative (PID) controller. Several representative simulations are performed to demonstrate the merits of the proposed method over the related control strategies. And the promising prospect of the UDE-based control in the practical application is further illustrated by conducting a water level control experiment.

Optical filter wavefront distortion: out-of-band to in-band predictions and the effect of the illumination source bandwidth.

The wavefront distortion (WFD) of a surface with an optical filter coating is ideally measured at the operating wavelength (λ) and angle of incidence (θ) of the filter. However, this is not always possible, requiring that the filter be measured at an out-of-band wavelength and angle (typically λ=633n m and θ=0∘). Since the transmitted wavefront error (TWE) and reflected wavefront error (RWE) can depend on the measurement wavelength and angle, an out-of-band measurement may not give an accurate characterization of the WFD. In this paper, we will show how to predict the wavefront error (WFE) of an optical filter at the in-band wavelength and angle from a WFE measurement at an out-of-band wavelength and different angle. This method uses (i)the theoretical phase properties of the optical coating, (ii)the measured filter thickness uniformity, and (iii)the substrate's WFE dependence versus the angle of incidence. Reasonably good agreement was achieved between the RWE measured directly at λ=1050n m (θ=45∘) and the predicted RWE based on an RWE measurement at λ=660n m (θ=0∘). It is also shown through a series of TWE measurements using a light emitting diode (LED) and laser light sources that, if the TWE of a narrow bandpass filter (e.g.,an 11nm bandwidth centered at λ=1050n m) is measured with a broadband LED source, the WFD can be dominated by the chromatic aberration of the wavefront measuring system-hence, a light source that has a bandwidth narrower than the optical filter bandwidth should be used.

Parameter Optimization and Development of Mini Infrared Lidar for Atmospheric Three-Dimensional Detection.

In order to conduct more thorough research on the structural characteristics of the atmosphere and the distribution and transmission of atmospheric pollution, the use of remote sensing technology for multi-dimensional detection of the atmosphere is needed. A light-weight, low-volume, low-cost, easy-to-use and low-maintenance mini Infrared Lidar (mIRLidar) sensor is developed for the first time. The model of lidar is established, and the key optical parameters of the mIRLidar are optimized through simulation, in which wavelength of laser, energy of pulse laser, diameter of telescope, field of view (FOV), and bandwidth of filter are included. The volume and weight of the lidar system are effectively reduced through optimizing the structural design and designing a temperature control system to ensure the stable operation of the core components. The mIRLidar system involved a 1064 nm laser (the pulse laser energy 15 μJ, the repetition frequency 5 kHz), a 100 mm aperture telescope (the FOV 1.5 mrad), a 0.5 nm bandwidth of filter and an APD, where the lidar has a volume of 200 mm × 200 mm × 420 mm and weighs about 13.5 kg. It is shown that the lidar can effectively detect three-dimensional distribution and transmission of aerosol and atmospheric pollution within a 5 km detection range, from Horizontal, scanning and navigational atmospheric measurements. It has great potential in the field of meteorological research and environmental monitoring.

Super-channel spectrum saving optimization procedure in elastic optical networks

Optical networks have historically been overprovisioned for physical-layer conditions and capacity and, as such, operate uninterrupted over several years. By reducing system margins, network efficiency and cost savings could be improved without compromising network reliability. On the other hand, super-channel transmission has been identified as a suitable solution for supporting high-data-rate connectivity. NETCONF, along with YANG models, has been recognized as a software defined networking (SDN) configuration and management protocol enabling control in a vendor-neutral way. Moreover, the OpenConfig YANG model defines vendor-specific transmission parameters, such as modulation format and bit rate, within operational modes. This paper investigates the trade-off between super-channel quality of transmission (QoT) and spectrum saving by allowing slight subcarrier overlap and tight filtering, hence reducing system margins. An automatic spectrum-efficient super-channel optimization procedure is experimentally demonstrated using a 600 Gbit/s transponder in an SDN-controlled elastic optical network. The automatic procedure performs the adaptation of filter bandwidth and subcarrier spacing. The latter is effectively operated by transponder agents, without involving the SDN controller, thus reducing the margins while guaranteeing that the QoT enables savings of up to 25% of the spectrum.

Aluminum Nitride-Based Adjustable Effective Electromechanical Coupling Coefficient Film Bulk Acoustic Resonator.

The arrival of the 5G era has promoted the need for filters of different bandwidths. Thin-film bulk acoustic resonators have become the mainstream product for applications due to their excellent performance. The Keff2 of the FBAR greatly influences the bandwidth of the filter. In this paper, we designed an AlN-based adjustable Keff2 FBAR by designing parallel capacitors around the active area of the resonator. The parallel capacitance is introduced through the support column structure, which is compatible with conventional FBAR processes. The effects of different support column widths on Keff2 were verified by finite element simulation and experimental fabrication. The measured results show that the designed FBAR with support columns can achieve a Keff2 value that is 25.9% adjustable.

Balanced Microwave Transmission Lines, Circuits, and Sensors

This paper provides an overview of balanced (or differential-mode) structures operating at microwaves, including common-mode suppression filters, balanced filters and circuits with intrinsic common-mode suppression, and differential-mode sensors. The increasing interest for balanced structures within the framework of communication circuits and sensors, related to their major robustness against electromagnetic interference (EMI), noise, and environmental factors, is duly justified. Then the paper reports various approaches for the implementation of common-mode suppression filters, balanced filters and circuits (including narrowband and wideband filters, multi-band filters, power dividers, couplers and phase shifters), and differential-mode sensors (mainly devoted to the measurement of permittivity and related variables). Rather than providing a detailed analysis of the different considered implementations/approaches, the main goal of this review paper is to discuss, and compare in some cases, the main proposed strategies (pointed out in the up-to-date state-of-the-art) for optimizing the performance of the various differential-mode devices under study.

Спектральная излучательная способность переходных металлов X группы в области точки плавления

An experimental study of the normal spectral emissivity of technical nickel, palladium and platinum in the solid polished and liquid phases near the melting points was carried out by the radiation method. The emission measurement was recorded by the bandwidth of the applied narrowband filters. The dependence of metal emission on the wavelength in the range of the radiation spectrum 0.26−10.6 µm is obtained. A comparative analysis with the literature data of other authors is carried out. A theoretical calculation of the emission is given according to the classical electromagnetic theory — Hagen 's formula and Rubens.

V-Iq Based Control Scheme for Mitigation of Transient Overvoltage in Distribution Feeders With High PV Penetration

High penetration of rooftop photovoltaic (PV) systems in distribution feeders can give rise to overvoltage during peak generation hours. A well-known solution for this problem is Volt-VAR control method, in which PV inverters mitigate the overvoltage by reactive power absorption. The conventional Volt-VAR scheme calculates the reactive power reference based on a limited bandwidth V-Q droop controller. Although the conventional method is capable of steady-state voltage regulation, it is not effective against voltage overshoots caused by fast solar irradiance variations. In this paper, a new V-Iq based Volt-VAR control scheme is presented to suppress the transient voltage overshoots during cloud passing. In this method, the bandwidth of the Volt-VAR controller is increased to enhance its responsiveness to voltage variations. To prevent instability caused by unwanted interaction between the high bandwidth Volt-VAR controller and the voltage feedforward section of the inner control loop, a low pass filter is added to the feedforward path. Small signal analysis of the proposed method provides a guideline for designing the bandwidths of Volt-VAR controller and feedforward filter. The stability of the proposed method is assessed based on Lyapunov method. Hardware in the Loop (HIL) experimental results are presented to validate the proposed scheme.