Search

A simple technique for frequency-static multi-notch/transmission-zero (TZ) creation in RF filters with single- and dual-band bandpass transfer functions is presented. It is based on the direct connection of two identical inline filtering units without stopband TZs in an in-parallel configuration by means of unequal input/output transmission-line segments for each branch. Unlike in typical transversal-signal-interference and channelized filter architectures, the overall length of these connecting transmission-line segments for both branches is the same. Thus, the multi-notch/TZ generation in the whole filtering action is accomplished by differently distributing this total electrical length between the input/output transmission-line segments for the two branches. As such, enhanced selectivity in the filtering response with several embedded notches when compared to the filtering transfer function of an isolated branch can be obtained. To experimentally demonstrate the generality of this approach, two proof-of-concept filter prototypes corresponding to a 2$/$3-GHz microstrip dual-band bandpass filter (BPF) and a 62-GHz waveguide BPF are built and tested.

Dual Active Bridge (DAB) converter is well suited for off-board fast Electric Vehicle Charging Stations (EVCS) and in DC microgrid-connected EVCS applications. However, proper modification in DAB converter topology is crucial for fast charging, as the charging current is very high, and any oscillations would shorten the EV battery life. As per literature, DAB converter topology integrated with a series inductor at the output for EV battery charging reduces the output current ripple by 40%. However, as per our observation, potentially unstable dynamics are introduced in the system with the inclusion of an LC filter. This affects the controller stability; hence, these dynamics must be damped using active or passive damping. Passive damping is less efficient due to the considerable losses it produces, partly induced by low-frequency noise and partly from switching-frequency noise. Also, placing the damping at the selective resonant frequency is very complex. In comparison, active damping offers selective placement and loss reduction. This paper presents the DAB converter mathematical modeling using the generalized average model (GAM) and the average output current linearization model (AOCLM). The paper presents stability analysis and proposes a novel and robust approach to control the dynamics in the current and voltage control loops during EV charging, thereby reducing battery degradation. The charge flow to the battery is controlled using Constant Current Constant Voltage (CCCV) algorithm. The proposed scheme also eliminates the need for extra sensors by selectively attenuating the oscillations at the frequency of interest. The performance of the proposed model for EV fast charging application is verified using MATLAB/Simulink and experimentally validated in a real-time simulator OPAL-RT hardware platform.

In this letter, a compact electromagnetic (EM) structure for miniaturized notch filter design in standard silicon technology is presented. Unlike prior-art on-chip bandstop filters, this filter configuration achieves sharp selectivity and large notch attenuation depth by producing a strong coupling between the top layer (i.e., resonating stub-loaded input-to-output direct path) and the bottom layer (i.e., two spiral-line grounded resonators). Moreover, as these vertically-stacked layers are broadside coupled, the physical footprint of the EM structure is significantly reduced. To demonstrate the proposed principle of notch filter, a simplified lossless behavioral model using ideal lumped elements is developed and verified. In addition, EM simulations are performed for parametric studies. As proof of concept, a prototype is fabricated in 0.13- $\mu \text{m}$ bulk CMOS technology. The measurement results show that the designed filter exhibits a notch located at 19 GHz with an attenuation depth higher than 37 dB. The footprint, excluding the pads, is only 0.028 mm2 (${0.096}\times {0.296}$ mm $^{{2}}$). [ABSTRACT FROM AUTHOR]

The resonant frequency drift caused by the change in mechanical parameters will cause the servo mechanism of CNC machine tools, robots and other equipment to produce mechanical resonance again. To address this problem, we propose a novel identification method of mechanical resonance based on the Fibonacci principle and a novel design method of notch filters based on optimization theory. First, by using a multifrequency sinusoidal signal, we design a fast search algorithm to search for the drift resonance frequency online; then, we optimize the notch filter to achieve fast and real-time resonance suppression by optimization theory. Compared with commonly employed passive resonance suppression methods, the proposed method can rapidly identify the parameters, more accurately suppress the resonance, minimize the phase angle loss and maintain the stability of the system. Finally, we apply the method to a 2-mass system experimental platform. The experimental results show that the proposed method is superior to the conventional passive resonant suppression method under the resonant frequency drift and other states and has strong robust performance.

A single metal layer, multifunctional frequency selective surface with a very simple pattern of the unit cell, containing a U-shaped metal resonator on FR4 substrate, and working in the low GHz frequency range is proposed. The structure realizes dual linear polarization filtering at frequencies of 1.83 and 4.14 GHz with fractional bandwidths of 34.15% and 22.51% respectively, and linear-to-circular polarization conversion at 2.68 GHz, with 3.2 dB insertion loss (IL), 30-45° angular stability depending on the direction of arrival of the incident wave, and 22.01% axial ratio bandwidth. The dimension of the unit cell corresponds to 0.09, 0.13 and 0.21 fractions of wavelength at the three operational frequencies. The functionality of the proposed structure is assessed by simulation, circuital model, and experiment in anechoic chamber. Scalability is demonstrated by designs that work at different frequencies, tested by simulation.

In order to eliminate the influence of synchronous harmonic current caused by mass imbalance of magnetic bearing on attitude angular velocity measurement accuracy, a notch filter which can adjust the notch depth and center frequency is proposed. Firstly, the influence of synchronous harmonic current on the measurement accuracy of magnetically suspended control and sensitive gyroscope(MSCSG) is analyzed, and then a notch filter is designed which can adjust the notch depth and center frequency, and the measurement accuracy and stability of the system after eliminating synchronous harmonic current are analyzed. Simulation results show that the proposed method can effectively suppress the unbalance vibration torque and eliminate synchronous harmonic current. Finally, the correctness and effectiveness of the proposed method are verified by experiments. Experimental results show that the proposed method can reduce the vibration torque by 50% and improve the measurement accuracy of attitude angular velocity significantly. [ABSTRACT FROM AUTHOR]

This brief presents an analog baseband (ABB) circuit in a 0.13 $\boldsymbol{\mu }\text{m}$ SiGe technology for transmitter leakage cancellation and close-in blocker suppressions in fully duplex (FD) frequency-modulated continuous-wave (FMCW) radar. This ABB comprises a programmable gain amplifier (PGA) and a cascaded LPF/Notch hybrid, which incorporates a closed-loop (CL) reconfigurable low-pass filter (LPF) and an open-loop (OL) tunable notch filter. The adopted key topologies include active-R-C bi-quads and $\text{G}_{\mathrm{ m}}$ -C ones. In an FD FMCW transceiver, Tx leakage and close-in blockers are difficult to be eliminated in the RF domain, especially when leakage/blockers are very close to desired signals or even in-band in the frequency domain. This LPF/notch hybrid is proposed to solve this issue. The LPF and PGA provide bandwidth (BW)/gain programmability, while the $\text{G}_{\mathrm{ m}}$ -C bi-quad provides adaptable center frequency for a notch filter. With this adaption, the notch filter could be adjusted to match the leakage/blocker offset frequency. Thus, digitally discrete programmability and analog continuous tuning capability are combined in this solution for improving the overall front-end interference robustness without de-sensitizing the Rx. Furthermore, the order of LPF/notch hybrid is programmable from 2 to 10 with a step of 2 for different rejection levels of interferences. The measured chip achieves a −3dB bandwidth of 6 ~ 21 MHz with 4-bit digital control and 1 MHz/step programmability, and a voltage gain of 0 ~ 70 dB with 9-bit digital control (3-bit from pre-amplifier, and 6-bit from PGA with 1 dB/step). With the condition of 15 dB gain, output P−dB is 11.8 dBm@3MHz, and the output IP3 is 20.8 dBm@3MHz. [ABSTRACT FROM AUTHOR]

A transformer-based notch filter is proposed in this article. The notch filter is integrated into a three-coil transformer in the matching network. While the primary coil and the secondary coil build a magnetically coupled resonator (MCR) and transfer the in-band signal to the next stage, the tertiary coil is coupled with the primary coil to absorb the interferers. Resonating with the switched capacitors, the notch frequency can be tuned digitally. A cross-coupled pair can further enhance the quality factor of the tank and, therefore, the rejection level. A low-noise amplifier (LNA) for Ku-band satellite communication with the proposed notch filter is implemented in 65-nm CMOS to verify the theory. The LNA achieves a measured power gain of 19.5 dB at 12.2 GHz with a −3-dB bandwidth of 9.2–12.7 GHz. The LNA can achieve 13.5-dB gain suppression at 13.9 GHz. The suppression level can be enhanced by tuning the quality factor of the active notch filter, which consumes up to 0.6 mW. The noise figure (NF) is 2.3 dB at 10.6 GHz and the NF is below 2.7 dB from 9.2 to 12.7 GHz. The input return loss is better than −15 dB from 8.8 to 18.5 GHz. The LNA consumes 5.9 mW from a 1-V supply. The whole chip occupies an area of 1000 $\times 800\,\,\mu \text{m}^{2}$. [ABSTRACT FROM AUTHOR]

In this article, we deal with the development of a fractional-order notch filter (FONF) for a grid-connected solar photovoltaic (PV) system. The developed FONF control approach is used to estimate fundamental active constituents from the distorted load currents, and hence, gating pulses for operating voltage source converter (VSC) are used in the PV system. This control approach for the grid-connected solar PV system is designed to achieve several purposes, such as feeding active power demand of the load/grid and countercurrent-related power quality issues at the common connecting point. The power quality issues taken into consideration are harmonics distortion, reactive power burden on the system, and unbalancing of connected loads. The FONF-based control proposes a modified structure of an integer-order notch filter. The integer-order filters have a limitation due to the fixed integrator and differentiator terms. In FONF, the power of integrator used in a notch filter can be modified according to the application required for obtaining the accurate response of the system. A prototype of the grid-connected solar PV system is developed in the laboratory using IGBTs based VSC and dSPACE MicroLabBox (DS-1202) to demonstrate the behavior of the FONF-based control. Simulation and experimental results are obtained for steady-state and unbalanced loads with variation in the solar irradiance. The harmonic distortions in the system are observed as per the IEEE-519 standard. [ABSTRACT FROM AUTHOR]

Interference-based microwave photonic notch filters (MPNFs) provide large rejection through destructive interference of radio frequency signals generated by beating a carrier with the upper and lower modulation sidebands. The two modulation sidebands are designed to have an amplitude imbalance and phase shift of $\pi$ between them. In many schemes, large rejection is achieved at the desired radio frequency by balancing the amplitudes of the modulation sidebands using stimulated Brillouin scattering (SBS) based gain or loss. However, the combined dispersion of the Brillouin active medium and other components detunes the phase difference between the sidebands away from $\pi$ , which causes a reduction in the notch depth. Dynamic dispersion control is, therefore, desirable for compensating dispersion-induced notch depth reduction. Here, we report dispersion-compensation exploiting bias-dependent phase of the modulation sidebands of a z-cut intensity modulator. We demonstrate a high-resolution ($\sim$ 50 MHz) MPNF with a large rejection of $>$ 65 dB over 1–25 GHz. To demonstrate the applicability of our MPNF in the presence of radio frequency interference, we suppress an interferer by 49 dB without affecting the signal. Such dispersion-compensated MPNFs are of importance in the sphere of Industry 4.0 based applications such as frequency measurement. [ABSTRACT FROM AUTHOR]

This paper develops an improved non dominated sorting genetic algorithm II (NSGA-II) based on objective importance vector γ, abbreviated as γ-NSGA-II. Different importance levels for the multiple objectives are incorporated in the objective importance vector, which is applied to determine the individual selection of sorting individuals in the critical layer. And such an individual selection strategy is developed to the NSGA-II algorithm in order to obtain the optimized solution for a task which has multiple objectives with different importance. The differences between the γ-NSGA-II algorithm and the traditional NSGA-II algorithm are discussed in detail. A notch filter is designed for the conducted emission suppression of a transformer rectifier unit (TRU) used in C919 flight testing, and then the parameters optimization design of a notch filter is discussed and conducted based on the γ-NSGA-II algorithm. The non-linear relationship between the filter's parameters and the suppression effect of the conducted emission is also discussed with the help of an electromagnetic compatibility (EMC) evaluation model based on a back propagation (BP) neural network. The experimental results show that the optimized design of the notch filter is effective and the improved γ-NSGA-II algorithm be more specific.

In active magnetic bearings (AMBs) supported rigid rotor systems, the unbalance compensation strategy based on a notch filter was often used to suppress the synchronous unbalance vibration when the rotor operates in the steady-state rotational speed. Whereas the rotor operates in a rotational-speed range including the critical rotational speeds, conventional notch filters should be improved to suppress the unbalance vibration. In most cases, improving the structure of the notch filter, such as a cross-feedback notch filter, phase-shift notch filter, adding the polarity switch or two-stage switch, was considered to make the notch filter work in the rotational-speed range. However, the improved notch filter may affect the stability of the AMBs rotor systems and result in large vibrations when the polarity switch or two-stage switch shifts. To avoid the shortcomings of these methods, a method using a variable angle compensation algorithm was proposed to suppress the synchronous unbalance vibration in finite iterative seeking processes, directly realizing unbalance compensation according to real-time rotor position. Finally, the effectiveness of the method proposed is verified by simulation and experiment results. [ABSTRACT FROM AUTHOR]

A class of multi-resonant RF filtering stage that exhibits a multi-band bandpass filtering transfer function with embedded in-band notches is presented. It is derived from the application of a composed lowpass-to-multi-passband/multi-stopband frequency transformation that converts the normalized lowpass prototype into the proposed multi-passband/multi-embedded-notch filtering cell. Thus, when employed in higher-order filtering networks, high-selectivity multi-band bandpass-filter (BPF) counterparts with embedded in-band stopbands are synthesized. Furthermore, two different approaches for out-of-band transmission-zero (TZ) generation in these type of filters to achieve sharp-rejection characteristics into them are detailed. The operational foundations of the engineered multi-passband/multi-embedded-notch filtering stage are described, along with several illustrative first-to-multi-order theoretical design examples with/without stopband TZs. Moreover, for experimental-demonstration purposes, a proof-of-concept microstrip prototype of a third-order dual-band BPF with two and one embedded notches in its lower and upper transmission bands, respectively, is manufactured and characterized. [ABSTRACT FROM AUTHOR]

In this article, a novel low-power notch-enhanced active filter is presented using the feedback notch-enhanced (FNE) technique. The active notch filter is proposed based on an area-saving second-order $LC$ series resonator. The passive devices’ loss can be effectively eliminated by the generated dc power-independent negative resistance by inserting a current feedback transistor. Moreover, the capacitive source degeneration (CSD) technique is proposed to boost the filter $Q$ by shifting the series resonant frequency to the negative-resistance region. To demonstrate the feasibility and practicability of the proposed notch filter, a 3.1–10.6-GHz IEEE 802.11a interferer rejected low-noise amplifier (IR-LNA) is fabricated in a 0.13- $\mu {\hbox {m}}$ CMOS process. The multistage structure, consisting of a common-gate (CG) stage with a dual-resonance load and a cascode stage with the proposed active notch filter, is employed for wideband input matching, gain flatness, and interferer rejection (IR) simultaneously. The measurements show that the IR-LNA provides a maximum of 16.05-dB power gain, 2.08–3.70-dB noise figure (NF) in the desired band, and a maximum of 40.9-dB IR ratio (IRR) at 5.77 GHz, with a power consumption of 10.2 mW, while the active notch filter only consumes 456- $\mu {\hbox {A}}$ current. [ABSTRACT FROM AUTHOR]

The frequency response characteristics of the hydraulic shaking table show the same as that of a two degree of freedom (DOF) resonance system due to the structural flexibility of the hydraulic shaking table. The hydraulic shaking system induces an anti-resonant peak during the working frequency band, which substantially reduces band width of the shaking table. The frequency response influence factor like mass, stiffness, and damping of the reaction wall are studied in this paper. The feed-forward control strategy is proposed in shaking system, which eliminates the effect of zero points at the anti-resonant peak and poles nearly the imaginary axis, broadens the bandwidth, and improves the control precision of the system. The notch filter is used to reduce the magnitude of resonant peak at the nature frequency of servo valve. The experimental results show that the proposed algorithm properly compensates the effect of structural flexibility and improves the bandwidth of the shaking system.

A double-layer frequency selective surface (FSS) built on FR4 substrate exhibiting two notch frequencies in the 0-10-GHz range is introduced. Recently published examples demonstrate that further research needs to be undergone for obtaining separate tuning of the resulted notch frequencies. Thus, this issue is addressed in this paper: the notch frequencies can be quasi-independently set by appropriate values given to the geometrical parameters of the two metal patterns in the unit cells of the structure. The FSS behavior is stable with respect to the angle of incidence of impinging electromagnetic waves up to 45°, as proved by simulation and validated by experiments.

Electroencephalogram (EEG) is a common tool for medical diagnosis, cognitive research, and managing neurological disorders. However, EEG is usually contaminated with various artifacts, making it difficult to interpret EEG data. In this study, a recursive least square (RLS) notch filter was developed to effectively suppress electrocardiogram (ECG) artifacts from EEG recordings. ECG artifacts were estimated and modeled using the instantaneous frequency of the cardiac cycle. Then it was adaptively estimated using a RLS filter and directly subtracted from contaminated EEG data. Based on the validation measures of improvement of normalized power spectrum (INPS), mean square error (MSE) and information quantity (IQ), the performance of ECG artifacts suppression was compared among the proposed RLS approach, independent component analysis (ICA) and blind deconvolution method under information maximization (Infomax) on simulated and animal experimental data. Simulation data demonstrated that INPS of RLS method (19.75(18.37,20.95) dB) was significantly higher than that of ICA (4.35(3.35,5.41) dB) and Infomax (5.76(4.60,6.88) dB). Meanwhile, MSE of RLS method (0.20(0.08,0.53) μV2) was considerably lower than that of ICA (5.59(2.35,19.79) μV2) and Infomax (3.21(1.01,10.69) μV2). Animal experimental data showed that INPS was 1.76(0.42,9.40) dB for RLS method, which was dramatically higher than that of ICA (0.02(0.00,0.14) dB) and Infomax (0.57(0.08,2.45) dB). The calculated IQ for RLS method (0.331(0.021,0.584)) was relatively lower than that of raw EEG (0.350(0.070,0.586)), ICA (0.350(0.069,0.581)) and Infomax (0.341(0.050,0.585)). The RLS notch filter can effectively eliminate ECG artifacts from EEG and preserve the majority of EEG information with little loss.

A novel scheme of an all-dielectric metasurface with double-layer patch array is proposed to achieve the highly tunable, narrowband notch filtering across visible and near-infrared range. The all-dielectric metasurface presents efficient blocking (transmittance 0.01-0.0001) at targeted wavelength and high (>93%) transmission across the visible and near-infrared light range outside the targeted wavelength band. The bandwidth of the notch filter could be greatly compressed with this all-dielectric metasurface, compared with those typical interference notch filters for distinctive wavelengths. The effect of the geometrical parameters on the spectral filtering of this metasurface is studied to provide a distinct relationship to design the desired narrowband notch filter conveniently. And the antireflection effect of the top silicon dioxide layer is verified with similar bandwidth, lower transmission at notch filtering wavelength and higher transmission at other wavelengths. In addition, the optical Fano resonance excited by the all-dielectric metasurface is responsible for the spectral filtering feature including the deep blocking feature at the specific wavelength and high transmission at other wavelengths.

In this article, design and characteristics of 20-GHz electromagnetic bandgap (EBG) common-mode (CM) filters for microstrip (MS) and stripline (SL) differential pairs are considered. CM filter notch (resonance) frequency, depth, and width at the −15 dB level are calculated from the mixed-mode S-parameters. The agreement between the measured and modeled S-parameters of the baseline structures validates the models and allows for further numerical experiments. The systematic analysis of the trends for both MS and SL filter characteristics as functions of various geometrical and material design parameters is presented. Sensitivity to various technological features (conductor surface roughness, trapezoid shape of the traces, and line length imbalance) is also analyzed. It is shown that the MS EBG structure is more sensitive and less monotonic to most of the design parameters than those for the SL. This is attributed to the less electromagnetic field containment and more complex mode structure in the MS structures as compared to the SL. Systematic sensitivity analysis allows for an optimal design of the EBG CM notch filters for any printed circuit board layer where a differential pair runs. Though the analysis is presented for 20-GHz EBG filters, most of the trends would be applicable to the filters for the other frequencies. [ABSTRACT FROM AUTHOR]

In this article, impedance mismatch effects on the characteristics of common-mode (CM) electromagnetic bandgap (EBG) filters are studied using three-dimensional (3-D) full-wave numerical simulations. The CM EBG filters considered herein are designed using standard printed circuit board technology and contain either microstrip (MS) differential pairs running above the EBG plane, or stripline (SL) differential pairs running on one of the layers next to the EBG plane. First, the terminations are fixed at 50 Ω, and the effects of the differential line impedance variations on the EBG filter parameters are studied. Overall, the considered variations in the widths of the traces and edge-to-edge separation distances in both the MS and SL structures do not drastically deteriorate the performance of the EBG CM filters. Then impedances of the ports are set different from 50 Ω, and the effects of this mismatch on the baseline SL and MS EBG structures are studied. It is shown that lower port impedances may have significant effect on the characteristics of filters. In addition, baseline EBG filters are cascaded with unmatched four-port load, and this may also deteriorate performance of filters. [ABSTRACT FROM AUTHOR]

A position sensorless operation of a doubly-fed induction generator (DFIG) is desired from considerations of cost, maintenance, cabling, and reliability. This article proposes two stator flux based model reference adaptive observers (SF-MRAOs) for the estimation of the rotor speed and position in a stand-alone DFIG. The cross product of the reference and estimated stator flux linkage vectors is fed as controller input in the existing method, thereby, making the observer model nonlinear. The first proposed method, which is based on notch filtering, offers a performance comparable to that of the existing method while reducing the number of voltage and current sensors required. The second proposed method linearizes the error input to the controller, making the controller design straight forward, and also leading to superior performance than the existing methods. The linearized SF-MRAO is shown to work successfully with good dynamic performance in vector control of a stand-alone DFIG. This article also shows that the proposed linearized SF-MRAO can be employed for obtaining the rotor current angle in direct voltage control of a stand-alone DFIG. Simulation and experimental results are presented from a laboratory prototype of a 10-hp DFIG coupled to a squirrel-cage induction motor. The sensitivity of the performance of the proposed linearized SF-MRAO to variations in machine parameters is also studied theoretically and experimentally. [ABSTRACT FROM AUTHOR]

Droop-controlled distributed energy resource converters in dc microgrids usually show low output impedances. When coupled with ac systems, second-order harmonics typically appear on the dc-bus voltage, causing significant harmonic currents at the converters resource side. In this paper, we show how to reduce such undesired currents by means of notch filters and resonant regulators included in the converters control loops. The main characteristics of these techniques in terms of harmonic attenuation and stability are systematically investigated. In particular, it is shown that the voltage control-loop bandwidth is limited to be below twice the line frequency to avoid instability. Then, a modified notch filter and a modified resonant regulator are proposed, allowing to remove the constraint on the voltage loop bandwidth. The resulting methods (i.e., the notch filter, the resonant regulator, and their corresponding modified versions) are evaluated in terms of output impedance and stability. Experimental results from a dc microgrid prototype composed of three dc–dc converters and one dc–ac converter, all with a rated power of $\text{5 kW}$ , are reported. [ABSTRACT FROM AUTHOR]

The vibration suppression in the presence of gyroscopic effects is an important issue for safe operations in magnetic bearing levitated varying speed rotor system. This paper proposes a synchronous vibration control method with a two-stage notch filter for the magnetically suspended rotor system with strong gyroscopic effects. First, the dynamics of the magnetically suspended rotor system with synchronous vibrations in the rotational motion is modeled. Then the proposed two-stage notch filter is designed and the solution of the two-stage switching point is derived to distinguish low speed and high speed. Stability analysis is also presented in the low-speed region and the high-speed region, respectively. Finally, simulation results demonstrate that the stability can be guaranteed by adjusting the phase shift angle of the notch filter over the entire speed range. Further experimental results confirm the effectiveness of the proposed suppression method. [ABSTRACT FROM AUTHOR]

The frequency multiplier with broadband frequency divide-by-2 followed by wide locking-range frequency tripler is presented in this article. The frequency divide-by-2 provides the quadrature signals with good mismatch performance across the entire operating frequency. The frequency tripler is quadrature locked while providing high fundamental tone rejection. The notch filtering with the source degeneration removes the harmonic tone due to the injected signal from the frequency divide-by-2 and minimizes the signal loss at the desired output frequency without additional current consumption. The proposed notch filter embedded within the injection-locked frequency tripler (ILFT) decouples the strict tradeoff between the selectivity (harmonic rejection) and the locking range, and thus enables the optimization of both parameters simultaneously. Quadrature outputs maintain good quadrature relations across the wide locking range based on the proposed layout and injection methods. The proposed circuit is fabricated in 45-nm CMOS technology. From the measurement result, the frequency multiplier achieves 25.61 dBc of harmonic rejection ratio without any additional bandpass filtering stages and exhibits the 57.6% of locking range corresponding to 20.4–36.6-GHz output frequency in the locked condition. The frequency multiplier with a multiplication ratio of 1.5 consumes 68 mA and occupies only $490\,\, \mu \text{m}\,\,\times 560\,\, \mu \text{m}$ of chip-area operated from the 1.2 V of supply voltage. [ABSTRACT FROM AUTHOR]

Workflow of electromagnetic bandgap (EBG) common-mode (CM) filter design of edge-coupled differential pairs on a printed circuit board (PCB) and sensitivity of its characteristics to variations of geometrical and material parameters are discussed. A number of simple 20-GHz EBG CM notch filters for differential stripline pairs are designed using full-wave numerical electromagnetic modeling, fabricating, and testing. The cases of one and two stripline differential pairs crossing the EBG patches are considered. The modeled and measured mixed-mode S-parameters are analyzed as functions of geometrical parameters, including size and number of EBG patches, gaps between them, geometry and position of signal traces across the EBG patches, and thicknesses of dielectric layers. The agreement between the measured and modeled mixed-mode S-parameters validates the models and allows for further numerical experiments. It is shown that the EBG filter performance depends on various subtle technological features, e.g., conductor surface roughness on metal surfaces; length imbalance on a differential pair; rate of coupling of lines within each differential pair and between the pairs; and some other factors. The systematic analysis of the trends for filter characteristics as functions of various design parameters allows for an optimal design of the CM notch filter. [ABSTRACT FROM AUTHOR]

The detection of wind turbines in a strong clutter background is analyzed at variance of polarimetric synthetic-aperture radar (SAR) configurations. The area of interest is the intertidal zone near Jiangsu, China and two detectors are used, the polarimetric notch filter (PNF) and a change detector that optimizes the ratio between covariance matrices. The detection performance is quantitatively analyzed using the receiver operating characteristic (ROC) curve, while the scattering mechanisms that characterize wind turbines are analyzed using the Yamaguchi decomposition. Experimental analysis shows that: 1) wind turbines result in a nontrivial scattering mechanism and 2) full-polarimetric measurements achieve the best detection performance independently of the two detectors. [ABSTRACT FROM AUTHOR]

A novel scheme of an all-dielectric metasurface with double-layer patch array is proposed to achieve the highly tunable, narrowband notch filtering across visible and near-infrared range. The all-dielectric metasurface presents efficient blocking (transmittance 0.01–0.0001) at targeted wavelength and high (>93%) transmission across the visible and near-infrared light range outside the targeted wavelength band. The bandwidth of the notch filter could be greatly compressed with this all-dielectric metasurface, compared with those typical interference notch filters for distinctive wavelengths. The effect of the geometrical parameters on the spectral filtering of this metasurface is studied to provide a distinct relationship to design the desired narrowband notch filter conveniently. And the antireflection effect of the top silicon dioxide layer is verified with similar bandwidth, lower transmission at notch filtering wavelength and higher transmission at other wavelengths. In addition, the optical Fano resonance excited by the all-dielectric metasurface is responsible for the spectral filtering feature including the deep blocking feature at the specific wavelength and high transmission at other wavelengths. [ABSTRACT FROM AUTHOR]

We propose a novel single-notch microwave photonic filter (MPF) using a nonsliced amplified spontaneous emission (ASE) source and a laser diode (LD). The nonsliced ASE is used for implementation of a phase tunable bandpass MPF, where the participation of an LD enables the simultaneous realization of an allpass MPF, without adding more devices into the system. By destructive interfering between the bandpass MPF and the allpass MPF, a single-notch MPF can be achieved with tunable center frequency. Compared with previous approach based on ASE source, the proposed approach has a broader tunable frequency range and a much simpler configuration since it is free from both the wavelength-division-multiplexer (WDM) and polarization processing. The proposed method is theoretically analyzed and experimentally demonstrated. [ABSTRACT FROM AUTHOR]

The use of LCL filters is a well-accepted solution to attenuate the harmonics created by the pulsewidth modulation. However, inherently LCL filters have a resonance region where the unwanted harmonics are amplified, which can compromise stability. Several techniques have been developed in order to tackle this issue. At first the use of passive damping, by intentionally increasing the resistance of the LCL filter components, is a simple, robust, and straightforward solution; however, it decreases the overall efficiency of the system, and hence in general is unwanted. Alternatively, active damping strategies, where the resonance damping is provided by the current controller, are of major interest. This paper analyzes the robustness of the closed-loop dynamics when different active damping techniques are implemented. The analyzed active damping techniques, which have been selected because of their readiness and simplicity, are: 1) filtered capacitor voltage feedforward and 2) second-order filters in cascade with the main current controller. The impedance/admittance stability formulation is used to model the system, which has been proven to be very convenient for the assessment of robustness. Experimental tests are provided in order to show the accuracy of the analysis and verify the findings. This paper proves that filtered capacitor voltage feedforward is a more robust and reliable solution than implementations based on cascade notch filters. [ABSTRACT FROM AUTHOR]

Mechanical resonance is a common problem in drive systems with elastic coupling. On-line adaptive notch filter is widely used to make systems stable and the key of this method is to identify natural torsional frequency from a speed feedback signal. However, because of common adoption of digital control and expansion of system bandwidth, oscillation frequency of the system is more likely to deviate from natural torsional frequency to a higher one. When oscillation frequency is shifted, the enabled notch filter with erroneous notch frequency causes an oscillation with a lower frequency and even makes resonance more severe. In order to explain this phenomenon, the classical two-mass model based classification of resonances is checked at first. Then, by taking digital control, current loop delay, and saturation nonlinearity into consideration, an improved digital mechanical resonance model is proposed and a criterion for oscillation frequency deviation is finally obtained. Furthermore, a more widely applicable and robust notch filter tuning strategy with no oscillation rebound is presented. In the end, the validity of aforementioned analysis and strategy is verified by experimental results. [ABSTRACT FROM AUTHOR]

For a magnetically suspended control moment gyro (MSCMG), the mass imbalance of the high-speed magnetically suspended rotor (MSR) will induce a synchronous force, which is the main disturbance for the attitude control of satellites. In this work, an elimination method with an adaption to parameter variations in an amplifier model is presented. First, the MSR system with a hybrid magnetic bearing is modeled. Next, a generalized notch filter is utilized to identify the synchronous displacement, according to which a feedforward controller is designed to generate synchronous current so that the electromagnetic force can counteract the permanent magnetic force precisely. To keep the feedforward controller unaffected by the power amplifiers whose parameters vary with the temperature, another notch filter is adopted to obtain the synchronous coil current, and then two types of adaptive controllers, which can tune the synchronous feedforward controller adaptively, are proposed and compared. Finally, simulations and experiments are carried out to demonstrate the validness of the adaptive control methods in an MSCMG test rig. The proposed control strategy does not need an accurate MSR model, and the methods of adaption to parameter variations in the amplifier model are suitable for various applications according to the elimination precision and computational effort. [ABSTRACT FROM AUTHOR]

LCL-filter-based grid-tie inverters require damping for the current-loop stability. There are only software modifications in active damping, whereas resistors are added in passive damping. Although passive damping incurs in additional losses, it is widely used because of its simplicity. This paper considers the active damping in medium-voltage parallel inverters for wind turbines. Due to cost reasons, only minimal software changes are allowed and no extra sensors can be used. The procedure must be robust against line-inductance variations in weak grids. Double-update mode is needed so the resonance frequency is under the Nyquist limit. The bandwidth reduction when using active damping is also required to be known beforehand. Moreover, the design procedure should be simple without requiring numerous trial-and-error iterations. In spite of the abundant literature, the options are limited under these circumstances. Filter-based solutions are appropriate and a new procedure for tuning the notch filter is proposed. However, this procedure requires that the resistance of the inductors is known and a novel filter-based solution is proposed that uses lag filters. The lag filters displace the phase angle at the resonance frequency so that the Nyquist stability criterion is fulfilled. Simulations and experiments with a 100-kVA prototype validate the analysis. [ABSTRACT FROM AUTHOR]

A dual band and low phase noise Ku-band voltage-controlled oscillator (VCO) using 180-nm CMOS technology is presented in this brief. The proposed VCO employs a switched notch filter that can operate in the low and high band, which depends on the state of nmos transistor and has a quality factor that is higher than that of a conventional inductor–capacitor (LC) resonator. The proposed resonator doubles the quality factor compared to LC in the technology and reduces the total die area. The first band is realized by the switched interdigital resonator when a nMOS transistor is in the off state. Furthermore, the second band is realized by turning nmos transistor to the on state, which is located between two fingers in the proposed resonator. The chip is implemented in 180-nm CMOS technology, and found that the proposed VCO operates from 15.5 to 16.7 Hz (low band) and 16.6 to 17.4 GHz (high band). At 1.8-V power supply, the power consumption of the oscillator core is 5.4 and 7.2 mW in the low- and high-frequency bands, respectively. The measured phase noise is −107 dBc/Hz at 1 MHz offset from 16.7-GHz carrier frequency. [ABSTRACT FROM AUTHOR]

In this paper, the detrimental effects due to the inevitable dispersion of single-mode fibers for stimulated Brillouin scattering (SBS) based microwave photonic notch filters (MPNF) with sideband amplitude and phase control are investigated. With an inappropriate dispersion compensation, the experimental demonstration shows a notch center frequency shift of 8.3 MHz in maximum and a stopband rejection reduction by 21 dB for the MPNF. The simulation and experiment are in good agreement. Furthermore, the criteria of optimizing the filter performance are also discussed both theoretically and experimentally. These results can help design MPNF based on SBS and benefit other microwave photonic applications, which rely on the phase difference of optical waves. [ABSTRACT FROM AUTHOR]

Compact polarimetric data exploitation, especially in hybrid-polarimetric (HP) mode, is currently attracting increasing interest due to the new generation of synthetic aperture radar (SAR) systems. Recently, it has been demonstrated that the notch filter is useful for ship detection in either full- or dual-polarization (DP)-mode SAR images. In this paper, the notch filter investigation is further extended to HP SAR architecture for ship detection on the ocean surface. First, a version of the notch filter that is suitable for HP SAR is proposed based on the definition of the corresponding feature partial scattering vector from the covariance matrix of the HP SAR. Subsequently, a novel model characterizing the statistics of the notch distance of sea clutter in the HP mode is developed. Based on the statistical model, the threshold of constant false-alarm rate (CFAR) ship detection is theoretically and analytically derived, which allows the automatic and adaptive implementation for ship detection in varying sea backgrounds in practical applications. Experiments on the HP SAR data emulated from full-polarization L-band Aerospace Exploration Agency Advanced Land Observation Satellite Phased-Array type L-band SAR and C-band RADARSAT-2 SAR measurements validate not only the soundness of the proposed CFAR detection but also the high accuracy of the presented model in fitting HP SAR data. Furthermore, the notch filter and its CFAR realization provide the same benchmark for the comparison of the detectability of HP and conventional linear DP SAR data. Preliminary findings suggest that the detection performance of HP SAR is superior to that of DP SAR in ship observation. Therefore, the proposed CFAR method based on the notch filter provides a promising technique for the detection of ships using HP SAR data. [ABSTRACT FROM AUTHOR]

A class of RF multi-functional bandpass filter with multiple frequency-reconfigurable rejected bands that are embedded into its broad transmission frequency range is reported. This filter concept exploits an original tunable multi-band quasi-bandstop section as constituent block. In this manner, unprecedented levels of spectral adaptivity are obtained for its in-band notches. Among them: 1) independent control of center frequency and rejection level; 2) notch-combination capability to conform wider rejected bands and make their number dynamically selectable; and 3) generation of dual-band bandpass responses with adjustable bandwidth and inter-band transmission zeros. This results in controllable in-band stopbands with reconfigurable bandwidth, attenuation level, and filtering-profile type. The devised filter architecture, which is appropriate for dynamic multi-interference mitigation in broad-band RF receivers, is scalable to any number of arbitrary-order in-band notches. For proof-of-concept purposes, a UHF-band microstrip prototype with up to two tunable in-band second-order stopbands is manufactured and measured. [ABSTRACT FROM AUTHOR]

A new all-optical microwave photonic notch filter (MPNF) is presented. It is based on controlling the amplitude and phase of the optical carriers and RF phase modulation sidebands via a diffraction-based Fourier-domain optical processor. It has the ability of realizing a flat-passband, narrow-notch, and large-free-spectral-range amplitude response and a group delay response with very few ripples. The carrier and sideband optical phase controls enable a continuous notch frequency tuning operation to be realized without altering the response shape. The filter has a simple structure and a wide bandwidth as it only involves optical components. Experimental results demonstrate an MPNF that exhibits a flat passband with 35 dB, and low group delay ripples of

In this work, we experimentally validate and characterize the first phase-shifted polymer optical fiber Bragg gratings (PS-POFBGs) produced using a single pulse from a 248-nm krypton fluoride laser. A single-mode poly (methyl methacrylate) optical fiber with a core doped with benzyl dimethyl ketal for photosensitivity improvement was used. A uniform phase mask customized for 850-nm grating inscription was used to inscribe these Bragg structures. The phase shift defect was created directly during the grating inscription process by placing a narrow blocking aperture in the center of the UV beam. The produced high-quality Bragg grating structures, presenting a double dips, reject 16.3 dB (97.6% reflectivity) and 13.2 dB (95.2% reflectivity) of the transmitted power, being therefore appropriate for sensing or other photonic applications. Its transmission spectrum possesses two sharp transmission notches, allowing a significant increase in measurement resolution compared to direct interrogation of a single grating. The reflection and transmission spectra when multiple phase shifts are introduced in the fiber Bragg grating structure are also shown. The PS-POFBG's strain, temperature, pressure, and humidity characteristics have been experimentally analyzed in detail to assess their potential usage as sensors. [ABSTRACT FROM PUBLISHER]

Active magnetic bearings (AMBs) have achieved great advantages in the high-speed and high-power-density rotating machine. Various vibration control strategies based on the notch filter have been reported to reduce the rotor imbalance vibration. But, the study is still insufficient to determine why the vibration gets reduced. This paper addresses a concise and direct explanation of the effects of notch filter on the rotor imbalance vibration with AMBs. An analytic solution for the synchronous response of rotor imbalance is introduced using the simple planar rotor model and general notch filter method. Then, combined with practical matters, the amplifier of a heteropolar radial AMB is further specified to uncover the effect of motion induced voltage to rotor self-centering, as a comparison with the homopolar radial AMB. Since the developed motor is equipped with both types of radial AMBs, a detailed control design is exhibited based on the dynamics of rigid body motion. The traditional simplification of two-plane separate control is improved, and a centralized controller is constructed. The effects of the rotor imbalance vibration rejection are demonstrated by the simulation results and experiments in a 30-kW 60000-r/min permanent magnet motor. [ABSTRACT FROM PUBLISHER]

Radio stations can observe radio signals caused by coherent emissions due to geomagnetic radiation and charge excess processes mainly in the frequency band from 30 to 80 MHz. This range is highly contaminated by human-made radio frequency interference (RFI). In order to improve the signal-to-noise ratio, RFI filters are used to suppress this contamination. Infinite impulse response (IIR)-notch filters operate with fixed parameters and suppress several narrow bands. IIR filters are generally potentially unstable due to feedbacks; however, they are much shorter and more power efficient than finite impulse response filters. We implemented an NIOS virtual processor calculating new set of IIR filter coefficients, which are reloaded dynamically on-the-fly. Spectrum analysis of the 30–80-MHz band can also be supported by the Altera IP Cores. The NIOS adjusts the new coefficients of the filter checking whether the poles are inside the unique complex radius (a condition of stability) as well as tuning the width of the notch filter. Practical implementation was tested in the laboratory with signal and pattern generators. Laboratory results are very promising. The IIR filter follows the drifting frequencies over very wide ranges (even 15 MHz for investigated range of 30–80 MHz), keeping a suppression factor on a very high level (≥10). The novelty of this paper is an introduction of the adaptive IIR-notch filter, which has not been used in any previous experiment. [ABSTRACT FROM AUTHOR]

Small wind energy conversion systems (WECSs) are becoming an attractive option for distributed energy generation. WECSs use permanent-magnet synchronous generators (PMSGs) directly coupled to the wind turbine and connected to the grid through a single-phase grid-tie converter. The loading produced on the dc link is characterized by large ripple currents at twice the grid frequency. These ripple currents are reflected through the dc bus into the PMSG, causing increased heating and ripple torque. In this paper, the PMSG inverter is used to control the dc-link voltage. In order to avoid reflecting the ripple currents into the PMSG, the feedback dc-link voltage is passed through a filter. The Butterworth filters, notch filters, antiresonant filter (ARF) and moving average filter (MAF) are considered. For a fair comparison, formulas are provided to tune the filter parameters so that dc-link voltage control will achieve the selected bandwidth. The different filtering options produce different levels of torque ripple reduction. The notch filter, ARF, and MAF obtain the best results and there is a tradeoff between the filter implementation complexity, bandwidth, overshoot, and the torque ripple reduction. Simulations and experiments using a 2.5-kW PMSG turbine generator validate the proposals. [ABSTRACT FROM AUTHOR]

Low-noise linear regulators are critical for power supply regulation of noise-sensitive circuits, such as ADCs, phase-locked loops, and other mixed-signal/RF system-on-a-chip designs. A low-noise low-dropout (LN-LDO) regulator using switched-RC bandgap reference and a multiloop, unconditionally stable error amplifier for output capacitorless operation is presented in this paper. A sample-and-hold switched-RC filter is developed to reduce the noise of the bandgap reference and drain-side modulated current-mode chopping technique is proposed to reduce the flicker (1/f) noise of the error amplifier. A switched capacitor notch filter is utilized to filter out the residual chopping ripple of the error amplifier. Thermal noise of the current reference circuit which is significant at such low noise levels is also reduced by using a low-area penalty passive RC filter. These techniques reduce the total integrated output noise of the LDO in the 10 Hz to 100 kHz band from $95.3\;\mu {{\rm{V}}_{{\rm{RMS}}}}$ down to $14.8\;\mu {{\rm{V}}_{{\rm{RMS}}}} . The LDO delivers a maximum load current of 100 mA with a dropout voltage of 230 mV and a quiescent current consumption of 40\;\mu \rmA . It achieves a power supply rejection of 50 dB at 10 kHz for a programmable output voltage range of 1–3.3 V. Fabricated in a 0.25\;\mu \rmm CMOS process, the LDO core occupies an area of 0.18 mm2. [ABSTRACT FROM AUTHOR]

Resonant poles of LCL filters may challenge the entire system stability especially in digital-controlled pulse width modulation (PWM) inverters. In order to tackle the resonance issues, many active damping solutions have been reported. For instance, a notch filter can be employed to damp the resonance, where the notch frequency should be aligned exactly to the resonant frequency of the LCL filter. However, parameter variations of the LCL filter as well as the time delay appearing in digital control systems will induce resonance drifting, and thus break this alignment, possibly deteriorating the original damping. In this paper, the effectiveness of the notch filter-based active damping is first explored, considering the drifts of the resonant frequency. It is revealed that when the resonant frequency drifts away from its nominal value, the phase lead or lag introduced by the notch filter may make itself fail to damp the resonance. Specifically, the phase lag can make the current control stable despite of the resonant frequency drifting, when the grid current is fed back. In contrast, in the case of an inverter current feedback control, the influence of the phase lead or lag on the active damping is dependent on the actual resonant frequency. Accordingly, in this paper, the notch frequency is designed away from the nominal resonant frequency to tolerate the resonance drifting, being the proposed robust active damping. Simulations and experiments performed on a 2.2-kW three-phase grid-connected PWM inverter verify the effectiveness of the proposed design for robust active damping using digital notch filters. [ABSTRACT FROM AUTHOR]

A systematic study of the coupling at room temperature between ferromagnetic resonance and a planar resonator is presented. The chosen magnetic material is a ferrimagnetic insulator (yttrium iron garnet, YIG) which is positioned on top of a stop band (notch) filter based on a stub line capacitively coupled to a 50 Ω microstrip line resonating at 4.731 GHz. Control of the magnon-photon coupling strength is discussed in terms of the microwave excitation configuration and the YIG thickness from 0.2 to 41 μm. From the latter dependence, we extract a single spin-photon coupling of g0/2π = 162 ± 6 mHz and a maximum of an effective coupling of 290 MHz. [ABSTRACT FROM PUBLISHER]

An original RF design approach for the realization of fully reconfigurable planar multiband bandstop filters (BSFs) is reported. The engineered RF filtering topology allows independent control of its stopbands in terms of center frequency and bandwidth. It exploits the in-series cascade of K spectrally agile N -notch filtering cells that are connected through K-1 static impedance inverters to realize an N -band filtering transfer function with K th-order stopbands. Each of these multinotch cells is formed by N tunable resonators—center-frequency control—that interact with the same nonresonating node by means of different variable couplings—bandwidth control. Additional features of this tune-all multiband BSF architecture when compared with related prior-art devices are: 1) scalability to the synthesis of an arbitrary number of stopbands; 2) notch-spectral-merging capability into wider eliminated bands of the same order, which equivalently allows the intrinsic control, i.e., without RF switches, of the amount of active rejected bands; and 3) smaller physical size. The coupling-matrix modeling of the conceived multiband BSF scheme is presented. Moreover, its cointegration with other RF analog-processing actions in multifunctional components, such as bandpass filtering and power division, is investigated. For experimental-validation purposes, three UHF-band mechanically reconfigurable microstrip prototypes are developed and tested. They correspond to a dual-notch filter, a wideband bandpass filter with embedded notches in its tunable passband, and a Wilkinson-type power divider with inserted stopbands for dynamic multi-interference mitigation. [ABSTRACT FROM PUBLISHER]