Low-pass Filter Structure Research Articles

Design of a Microwave Quadrature Hybrid Coupler with Harmonic Suppression Using Artificial Neural Networks

In this paper, a compact and simple structure of an elliptic microstrip lowpass filter (LPF) is designed for harmonic suppression in microwave quadrature hybrid coupler (QHC) applications. A radial resonator and a rectangular resonator are used to produce an elliptic LPF. The proposed LPF is used on the outer sides of the branch line coupler, which has improved the coupler harmonic suppression. Furthermore, artificial neural networks (ANNs) are incorporated to improve the LPF design process. The LPF best structure is obtained using the proposed ANN model. The proposed LPF has a compact size, which only occupies 16.4 mm × 7.3 mm equals to 0.164 λg × 0.073 λg, has a cut frequency of 2.2 GHz, and shows a sharp transmission band with a roll-off rate of 158.3 dB/GHz. Finally, the deigned QHC operates correctly at 1 GHz, which shows high harmonic suppression ability. The proposed QHC provides wide suppression band from 2.25 GHz up to more than 14 GHz, which can effectively suppress 3rd, to 14th harmonics. The proposed coupler features desirable parameters of S11, S21, S31, and S41, with magnitude of −21 dB, −3.4 dB, −3.3 dB, and −22.5 dB, at the operating frequency. The proposed approach mitigates the complexity of the circuit fabrication, compared with the previous methods while achieved desirable performances for the proposed QHC.

A Wilkinson power divider with harmonic suppression through low-pass filter for GSM and LTE applications

Conventional Wilkinson power dividers (WPDs) perform satisfactorily near the intended operation frequency. Nonetheless, these WPDs demonstrate subpar performance in the stopband and necessitate a significant physical space. To enhance the existing level of advancement and in order to improve on the current state-of-the-art, a modified WPD is designed and fabricated, demonstrating a significant improvement in stopband and superior isolation between output ports. To improve the stopband and suppress unwanted harmonics, a low-pass filter (LPF) structure is placed in the both branches of the conventional WPD. The proposed modified WPD depicts a wide stopband bandwidth (fSB > 17.25 GHz) from 2.75 to over 20 GHz with an attenuation level of 20 dB, suppressing 2nd to 11th harmonics. According to measured results, the input return loss (|S11|), insertion loss (|S21|) and output isolation (|S32|) at f = 1.8 GHz are better than 33 dB, 3.2 dB and 21 dB, respectively. Indeed, the proposed modified WPD exhibits a magnitude imbalance of 0.00018, a phase imbalance of 1.25 degrees and a group delay of 0.5 ns. The proposed WPD depicts a compact size of 35 mm × 25 mm (0.38 λg × 0.27 λg), where λg is the guided wavelength at f = 1.8 GHz. There is a good agreement between the simulated and measured results. According to the obtained results, the proposed modified WPD shows a desirable performance for modern LTE and GSM communication applications.

A Modeling Approach for Designing New Acoustic Materials

In this study, mathematical modeling design based on Sound Transmission Loss measurement results of new acoustic material samples with natural content was carried out. Using the test samples in question, transfer function of acoustic materials based on electronic filter circuit design and a transition design method for the production of new acoustic materials by utilizing the transfer function is presented. Based on the experimental results of the test samples, it is the most suitable low-pass filter structure for the proposed design. In this study, active Sallen-Key low-pass filter structure is preferred and used. Sound Transmission Losses in dB (decibels) of acoustic samples were obtained experimentally for 500, 1000, 2000 and 4000 Hz. fundamental frequencies in the literature. Based on these data, transfer function simulation suppression gain results were obtained in TINA-TI program, active filter circuit designed, and MATLAB program. When the other results were compared in the experimental results, it was seen that very close values were obtained. It has been demonstrated that the proposed method can be used effectively in the design and examination of new acoustic materials.

Design Technique of K-Band CMOS Phase Shifter with L-C-L T-Type Low Pass Structure

In this study, we designed a 5-bit K-band CMOS switch type phase shifter. In order to minimize phase and gain errors, a design technique for bits constituting the phase shifter was proposed. The proposed design technique has been achieved by adjusting the resonant frequencies of inductance and capacitance in the L-C-L T-type low pass filter structure. Through this, a method of optimizing the phase shifter with the T-type low pass filter structure was presented. The K-band 5-bit phase shifter was designed with a 65 nm CMOS process to verify the feasibility of the proposed design technique. The core size was 0.78 × 0.21 mm2. At the frequency ranges of 22.0 to 23.0 GHz, the insertion loss and RMS phase and gain errors were measured to be 7.44 ± 2.0 dB, 2.6°, and 1.2 dB, respectively.

Experimental Investigation of Vibration Isolator for Large Aperture Electromagnetic MEMS Micromirror.

The Micro-Electro-Mechanical-System (MEMS) micromirror has shown great advantages in Light Detection and Ranging (LiDAR) for autonomous vehicles. The equipment on vehicles is usually exposed to environmental vibration that may degrade or even destroy the flexure of the micromirror for its delicate structure. In this work, a mechanical low-pass filter (LPF) acting as a vibration isolator for a micromirror is proposed. The research starts with the evaluation of vibration influences on the micromirror by theoretical calculation and simulation. The results illustrate that mechanical load concentrates at the slow flexure of the micromirror as it is excited to resonate in second-order mode (named piston mode) in Z-direction vibration. A specific LPF for the micromirror is designed to attenuate the response to high-frequency vibration, especially around piston mode. The material of the LPF is a beryllium-copper alloy, chosen for its outstanding properties of elasticity, ductility, and fatigue resistance. To measure the mechanical load on the micromirror in practical, the on-chip piezoresistive sensor is utilized and a relevant test setup is built to validate the effect of the LPF. Micromirrors with or without the LPF are both tested under 10 g vibration in the Z-direction. The sensor output of the device with the LPF is 35.9 mV in piston mode, while the device without the LPF is 70.42 mV. The attenuation ratio is 0.51. This result demonstrates that the LPF structure can effectively reduce the stress caused by piston mode vibration.

Novel Low-Pass Filter Structures Using Spur-Lines to Generate Additional Attenuation Poles

We propose two novel low-pass filter (LPF) structures that have generated additional attenuation poles from applying spur-lines to typical open-stub LPFs. The first structure has the spur-lines added to the serial lines, and the second structure has the spur-lines added to the parallel open stub. From the characteristic analyses of the filters with the proposed design, it was confirmed that the length of the spur-line was an important variable for controlling the stopband bandwidth and attenuation depth. The two types of LPFs were fabricated and then validated by the agreement between the theoretical and measured results. From the measured results, the stopband bandwidths of the serial- and parallel-configuration spur-line LPFs were improved by approximately 4.7 times and 1.4 times of the defined reference level, respectively, compared to that of the typical LPF.

A Miniaturized wide Stopband Low-pass Filter using T and Modified L Shapes Resonators

A new structure of microstrip-based low-pass filter with wide stopband and sharp roll-off is introduced, in this paper. In the proposed topology, resonators with T and modified L Shapes have been used. To improve the suppression factor and relative stopband bandwidth, the second resonator has been added to the first resonator. The designed filter has been fabricated on a 20 mm thickness RO4003 substrate, which has a loss tangent of 0.0021 and a relative dielectric constant equal to 3.38. All parameters including roll of rate, stopband, bandwidth, return loss, insertion loss, and figure of merit have significant coefficients. Simulation has been ran using advanced design system software. The 3dB cutoff frequency is appropriate. The value of the insertion loss parameter is <0.1 dB and the S11 parameter is −22 dB at this point. The stopband is extended from 2.42 up to 24 GHz, which shows an ultra-stopband. The results of the simulation and experiment are almost similar, which indicates a proper performance of the designed structure.

Design and fabrication of a Wilkinson power divider with harmonic suppression for LTE and GSM applications

Conventional Wilkinson power dividers (WPDs) can provide acceptable performance close to the nominal center frequency. However, these WPDs can also exhibit poor out-of-band performance while requiring a large footprint. In order to improve on the current state of the art, a modified microstrip WPD is proposed that exhibits a substantially improved stopband and high isolation. A lowpass filter (LPF) structure is utilized in both branches of the power divider to provide harmonic suppression. According to the obtained results, the input return loss (|S11|), output return loss (|S22|), output insertion loss (|S21|) and isolation (|S32|) are better than 34.2 dB, 26.2 dB, 3.52 dB and 31.2 dB, respectively. The proposed modified WPD has a wide 20 dB stopband (from 2.54 GHz to 13.48 GHz) and filters the second to seventh harmonics with attenuation levels of greater than 20 dB. The proposed WPD has a small size of 33.8 mm × 27 mm (0.42 λg × 0.33 λg), where λg is the guided wavelength at the operating frequency of 1.8 GHz. The WPD has been fabricated and tested and shows good agreement between simulated and measured results and the proposed design has desirable characteristics for LTE and GSM applications.

Grid-Forming Converter Overcurrent Limiting Strategy Based on Additional Current Loop

Compared with current source converters, voltage source converters (grid-forming converters) have better frequency support capabilities, voltage support capabilities, and regulation performance, thus they have broad application prospects. However, the grid-forming (GFM) converter has insufficient current control ability, and it easily causes problems such as overcurrent issues when a fault occurs. Thus, this insufficiency is one of the most important challenges the GFM converter is faced with. Aiming to solve the problems mentioned above, this paper proposes a control method of a GFM converter achieved with a low-pass filter structure and an additional current loop. The additional current loop controls the dq-axis current components by acting on the outer loop to generate appropriate phase and voltage amplitude reference. The low-pass filter structure is used to solve the system frequency stability problem caused by the inclusion of the additional current loop. On the premise of ensuring that the system frequency meets the grid-connection requirements, the proposed strategy rapidly limits the output current within the allowable range and guarantees expected voltage source characteristics of the converter during the fault period. Finally, the effectiveness and superiority of the proposed control strategy are verified by MATLAB/Simulink simulations.

Active disturbance rejection controller design for alleviation of gust-induced aeroelastic responses

This paper develops an active disturbance rejection control technology that uses the equivalent input disturbance (EID) approach to reduce the aeroelastic vibrations and structural loads caused by wind gusts. The influence of gust disturbance is evaluated by the EID estimator and actively compensated in the control input channel, giving a high disturbance rejection performance of the aeroelastic system. The suitable design of the state observer and low-pass filter is essential for the disturbance estimation and rejection. However, the conventional low-pass filter simply specified by a cutoff frequency may lead to a degraded estimation performance. To this end, a new structure of low-pass filter is proposed, and the design algorithms for the observer gain and filter parameters are also given. By specifying bandwidth constraints, the control system with guaranteed performance can be automatically generated. Numerical results show that for the acceleration measurement-based control, the proposed design method can achieve better disturbance estimation performance than that obtained by the conventional one, resulting in smaller gust responses. Finally, the proposed design method is further extended to the folding wing parameter-varying system. A parameterized version of the EID-based controller is constructed by using the concept of gain-scheduling. It is demonstrated that the gust responses can be significantly reduced in the entire range of folding angle. This study provides an effective solution for gust alleviation of the aeroelastic system with fixed or variable configurations.

A micromachined ultra‐wide stopband lowpass filter based on stepped impedance resonator loaded T‐shaped structure

This article presents an additively manufactured micro-coaxial lowpass filter with ultra-wide stopband suppression. To achieve a wide stopband response, two-stage stepped impedance resonator loaded T-shaped structures are used to substitute the low impedance transmission lines in the lowpass filter prototype to generate extra transmission zeros in the stopband. Shunt open-ended stubs are introduced to the structure in flexible positions to further strengthen the suppression at specific frequency points. The filter is designed with 22 GHz passband and the 20 dB stopband suppression bandwidth over 300 GHz. The micro-coaxial lowpass filter structure was fabricated based on additive metal micro-manufacturing process with the rectangular cross-section dimensions of 0.5 mm × 0.5 mm (300 GHz cutoff frequency). To facilitate the measurement, pair of coax-to-CPW transitions are added at the input/output ports. The measurement results show excellent agreement from DC-110 GHz (limitation of the measurement device), with insertion loss of 1.05 dB at the cutoff frequency fc, which validates the design.

Multivariate time series prediction of complex systems based on graph neural networks with location embedding graph structure learning

Graph convolutional neural networks (GNNs) have an excellent expression ability for complex systems. However, the smoothing hypothesis based GNNs have certain limitations for complex process industrial systems with high dynamics and noisy environment. In addition, it is difficult to obtain an accurate information about the interconnections of sensor networks in manufacturing systems, which brings challenges to the application of GNNs. This paper introduces a graph convolution filter with a serial alternating structure of low-pass filter and high-pass filter to alleviate the problem of node feature loss. Furthermore, we propose a simple and effective method to learn graph structure information during training. This method combines the advantages of graph structure learning based on metric method and direct optimization method. Finally, a spatiotemporal parallel feature extraction framework for multivariate time series prediction is constructed. Experiments are carried out on real industrial datasets, and the results demonstrate the effectiveness of the model.

A new configuration of a compact printed coplanar low pass filter with high rejection

The aim of this contribution is a new study on the achievement, fabrication and the test of a new low pass filter (LPF) coplanar structure based on periodic resonators. The proposed structure can be easly integrated with microwave devices, the validated LPF circuit has a wide band pass and high band stop. The design was done by two electromagnetic (EM) solvers one is based on moment method and the other one on finite integration technique. In order to reach a final LPF structure with good characteristics concerning the insertion loss of−0.8 dB and high attenuation until 15 GHz, the cut-off frequency of this filter is equal to 6,77 GHz. Many series of optimization were conducted using multiple algorithms. The whole area of the validated LPF is16×40 mm2.

Design of microstrip quint‐band lowpass–bandpass filters with flexible passband allocation

In this paper, newly proposed microstrip quint-band lowpass–bandpass filters are presented. The lowpass filter structure comprises a meandered transmission line and modified T-shaped resonators. Based on such an lowpass filter (LPF) structure, a quad-band λ/4 inductively-coupled dual-mode stub-loaded stepped impedance resonators BPF with one pair of a coupled I/O feeding line are parallelled on both sides of LPF to construct a quint-band lowpass–bandpass filter. By incorporating the parallel I/O coupled line and utilising multiple coupling paths, four bandpass bands can be fully controlled and designed independently. Specially, two distinct types of bandpass filters with different generating mechanisms are investigated and then combined to provide the quad-band responses. To validate the design concept, two types of quint-band lowpass–bandpass filters are designed, fabricated, and tested, where simulation results agree well with measurement results.

Extended Digital Programmable Low-Pass Filter for Direct Noise Filtering of Three-Phase Variables in Low-Cost AC Drives

This paper proposes an extended structure of a programmable low-pass filter (PLPF) for direct filtering of three-phase variables in automotive AC drives. The PLPF adjusts its cut-off frequency according to the synchronous frequency of the AC motors. Moreover, it compensates gain attenuation and phase delay of the fundamental component signal. The conventional PLPF can only be applied to variables in the stationary reference frame. In order to obtain filtered three-phase variables, an inverse reference frame transformation is required. However, the extended structure, which includes reference frame transformations, can be directly applied to three-phase variables and remove the noise in the earlier stage before transformation. The extended PLPF is more useful for making signal flows clear and intuitive when organizing an algorithm that directly requires three-phase variables. The extended PLPF requires a moderate computational load corresponding with that of the conventional PLPF because its formula is simplified by use of Kirchhoff’s law. The reduction in the execution time is critical for implementing the filter based on low-cost microcontrollers. Using case studies, dead-time compensations and open-phase fault detection for AC drives show the effectiveness of the extended PLPF.

Research on weak signal detection of integral average digital lock-in amplifier

In the process of detecting the amplitude and phase of the weak signal based on digital lock-in amplifier (DLIA), a low-pass filter (LPF) with an extremely low cut-off frequency is required. Even so, the effect is often not good. The detection results of amplitude and phase of weak signal are distorted and fluctuate sharply. To eliminate the difficulty of LPF design, and to reduce the distortion and output fluctuation of detection results of DLIA, this paper proposes a weak signal detection method based on integral average digital lock-in amplifier (IADLIA), which can be used for weak signal detection under strong noise. This method optimizes the structure of the traditional DLIA based on the principle of cross-correlation detection. And then this paper analyzes the influence of the cut-off frequency and signal-to-noise ratio of the LPF on the detection accuracy and output stability of the weak signal amplitude and phase. Finally, the corresponding weak-signal amplitude at the bearing rotating frequency is accurately detected by the proposed method, and the accurate identification of bearing faults is realized. The experimental results show that the IADLIA is characterized by stable output, strong anti-interference ability and high output accuracy. The proposed method can accurately detect the amplitude and phase information of the weak signal in a strong noise environment, get rid of the structure of LPF, and the overall performance is better than the traditional DLIA.

A compact lowpass/dual-band bandpass filter for microwave application

A combination of lowpass and dual band bandpass filter with improved selectivity is presented in this manuscript. Two circular split ring resonators which are connected at the upper side, provide a lowpass filter characteristics. In order to achieve combined lowpass with dual passband response two L-shape stubs are incorporated into the lowpass filter structure. The parametric analysis of the proposed filter has been carried out using CST microwave studio. The numerical result shows a 3-dB cutoff frequency for lowpass at 1.22 GHz, first and second passband resonant frequencies are 2.44 GHz and 3.7 GHz respectively. The proposed filter is compact and overall size of the proposed filter is 32.9 mm?15mm.

Design of Compact Planar Lowpass Filters by Using Fragment-Type Structure With Multi-Bit Scheme

A novel design method for compact planar lowpass filter (LPF) with prominent roll-off rate and wide stopband suppression is proposed by using fragment-type structures (FTS) with multi-bit scheme. The proposed multi-bit FTS design has the potential to achieve higher LPF performance at higher optimization efficiency, without any prerequisite knowledge about the pivotal LPF structures needed in conventional LPF designs. The definition of multi-bit FTS and the implementation of LPF design with multi-bit FTS scheme are presented in detail. Compared to the LPF design with 1-bit FTS, the 2-bit FTS design may use smaller decision space, take fewer iterations in multi-objective optimization searching, and yet achieve sharper roll-off rate, higher stopband suppression and a wider stopband. For demonstration, planar LPFs on PCB using the 1-bit FTS and 2-bit FTS are designed and tested. The 2-bit FTS design yields a sharp roll-off rate of 123.3 dB/GHz, a relative stopband bandwidth of 165% referred to stopband suppression of 20 dB, and a high figure-of-merit of 21060. Effects of the geometry parameters of the 2-bit elements are further discussed to give some guide rule on using the 2-bit FTS design.

Coplanar waveguide low pass filter based on square complementary split ring resonator with wide rejection

In this paper, we present a novel coplanar waveguide low pass filter (LPF) structure based on the use of square complementary split ring resonators (CSRRs) in order to enhance the performances of a low pass filter. Especially, to enlarge the bandwidth of the LPF, the insertion losses and to increase the rejection of the LPF. The CSRRs are optimised and inserted periodically along the center conductor of the CPW line with a CPW ground integrating stubs permitting to enlarge the bandwidth. The simulation results of this filter show a -3 dB cut-off frequency equal to fc = 5.28 GHz. The designed filter has a good rejection in the stop band which below -20 dB and presents a good insertion loss in the bandwidth. The proposed filter has been fabricated and tested which give a good agreement between simulation and measurement results, the whole dimensions of the validated filter are 35.48x21.16 mm2. The originality of this work is the wide rejection band and the miniature dimensions. © 2020, Universitas Ahmad Dahlan.

Miniaturized ultra-wideband coplanarwaveguide lowpass filter with extended stop band

<p class="Default">In this article, we propose a novel design of large rejected band of miniaturized ultra wide band (UWB) of a planar CPW low pass filter “LPF” based on the use of periodic elements of ‘e’ slots. The goal of this work is to develop a new structure of Low Pass Filter with the following criterion: Miniature, Compact and Easy for Fabrication. The Miniaturization of this structure is achieved by entering the 'e' slot in etching area in the ground of CPW line, to save the standard gap of the adapted coplanar line. The designed coplanar LPF is a compact filter having a large band pass and extended stop band, with the possibility to associate easily with others RF and microwave planar circuits. The entire area of the proposed structure of CPW LPF is 14.3x20 mm<sup>2</sup>.</p>