Bandstop Filter Research Articles

Blind Super-Resolution Network with Dual-Channel Attention for Images Captured by Sub-Millimeter-Diameter Fiberscope

A blind super-resolution network with dual-channel attention is proposed for images captured by the 0.37 mm diameter sub-millimeter fiberscope. The fiberscope can used in scenarios where other image acquisition devices cannot be applied based on its flexible, soft, and minimally invasive characteristics. However, the images have black reticulated noise and only 3000 pixels. To improve image quality, the Butterworth band-stop filter is used to reduce the frequency of the reticulated noise. By optimizing the blind super-resolution model, high-quality images can be reconstructed that do not require a lot of synthetic paired fiberscope image data. Perceptual loss is utilized as a loss function, and channel and spatial attention mechanisms are introduced to the model to enhance the high-frequency detail information of the reconstructed image. In the comparative experiment with other methods, our method showed improvements of 2.25 in peak signal-to-noise ratio (PSNR) and 0.09 in structural similarity (SSIM) based on objective evaluation metrics. The learned perceptual image patch similarity (LPIPS) based on learning was reduced by 0.6. Furthermore, four different methods were used to enhance the resolution of the fiberscope images by a factor of four. The results of this paper improve the information entropy and Laplace clarity by 0.44 and 2.54, respectively, compared to the average of other methods. Validation results show that the approach in this paper is more applicable to sub-millimeter-diameter fiberscopes.

MEMS-Switched Triangular and U-Shaped Band-Stop Resonators for K-Band Operation.

Triangular resonators re-shaped into Sierpinski geometry and U-shaped resonators were designed, linking them with single-pole-double-through (SPDT) RF MEMS switches to provide frequency tuning for potential applications in the K-Band. Prototypes of band-stop narrowband filters working around 20 GHz and 26 GHz, interesting for RADAR and satellite communications, were studied in a coplanar waveguide (CPW) configuration, and the tuning was obtained by switching between two paths of the devices loaded with different resonators. As a result, dual-band operation or fine-tuning could be obtained depending on the choice of the resonator, acting as a building block. The studied filters belong to the more general group of devices inspired by a metamaterial design.

A dynamically switchable multifunctional meta-device in terahertz based on vanadium dioxide and photosensitive silicon

In this study, we propose a dynamically switchable multifunctional device operating in the terahertz range. The device is designed by employing a multilayered planar structure that incorporates vanadium dioxide and photosensitive silicon films. We analyze the transmission characteristics and multifunctional attributes of the device. The device exhibits the capacity to transition among diverse functionalities, including linear polarization conversion, field intensity modulation, frequency selection, and wave absorption. The polarization conversion ratio exceeds 90%, and precise control over the amplitude ratio between cross-polarized and co-polarized fields is achievable. Field intensity modulation can be realized through any of three distinct methods. Upon activation of the frequency selection function, the device can effectively operate as a band-stop filter, yielding a -20dB bandwidth of 0.57 THz. Furthermore, in absorber mode, the device demonstrates a peak absorption efficiency of 90%.

A novel compact dual-band bandstop filter with enhanced rejection bands

A novel compact dual-band bandstop filter with enhanced rejection bands

Design and development of a piezoelectric-hydraulic hybrid actuator with quarter-wavelength tubes

The piezoelectric hydraulic actuator is a hybrid device consisting of a hydraulic pump driven by a piezoelectric stack connected to a hydraulic cylinder. For this type of piezoelectric actuator, the inertial force caused by the flow pulsation of the liquid will inhibit the movement of the piezoelectric vibrator and reduce its output performance. To solve these issues, two tubes were embedded into the piezoelectric-hydraulic hybrid actuation system for the first time to act as mechanical bandstop filters by interfering with the propagation of acoustic waves. The acoustic power transmission loss of the tube is derived from the one-dimensional wave equation. According to the experimental results, when the excitation frequency is close to the optimal operating frequency corresponding to the tubes, the liquid pulsation rate is reduced, the influence of inertial force on the actuator is weakened, and the output performance is relatively significantly improved. This strategy finally leads to a maximum no-load velocity of 153.5 mm s−1 and a maximum blocking force of 261.5 N for the hybrid actuator with 300 mm tubes; the maximum no-load velocity and blocking force of the hybrid actuator with 500 mm tubes are 94.45 mm s−1 and 230 N, respectively. Furthermore, this strategy can be used in other electrohydraulic actuators to enhance their capabilities.

Triangular Sierpinski Microwave Band-Stop Resonators for K-Band Filtering.

Triangular resonators re-shaped with Sierpinski geometry were designed, manufactured, and tested for potential applications in the K-Band. Prototypes of band-stop filters working around 20 GHz and 26 GHz, interesting for RADAR and satellite communications, were studied in a coplanar waveguide (CPW) configuration. Single and coupled structures were analyzed to give evidence for: (i) the tuning of the resonance frequency by increasing the internal complexity of the triangle and (ii) resonance enhancement when coupled structures are considered. The exploited devices were part of the more extended family of metamaterial-inspired structures, and they were studied for their heuristic approach to the prediction of the spectrum using experimental results supported by electromagnetic simulations. As a result, a Sierpinski resonator, not only fed into but also fully embedded into a CPW environment, had a frequency response that was not easily determined by classical theoretical approaches.

Design of dual-band power amplifier using bandstop filter and dual-mode bias circuit for multistandard transceiver systems

This paper presents a dual-band power amplifier (PA) using a meandered line bandstop filter (BSF). An important challenge addressed in this design is to achieve proper isolation between the operational bands of the amplifier. The proposed BSF provides isolation and efficiency, effectively separating the output power and power gain between the two operational bands. Additionally, a dual-mode bias circuit is designed to serve as an inductor choke and control the second harmonics for both operating frequencies simultaneously. Two dual-band PAs, utilizing LDMOS and GaN HEMT transistors, have been designed using the proposed output matching circuit, which incorporates the BSF, bias circuit, and compensation circuit. The results obtained from both PAs, employing different transistors, are identical. Based on the presented concepts, a dual-band PA with an LDMOS transistor has been fabricated and measured. The measurements reveal an efficiency of 79.23%, an output power of 39.85 dBm, and a power gain of 14.85 dB at a frequency of 0.7 GHz. Similarly, at a frequency of 1.9 GHz, the efficiency is 77.24%, the output power is 38.22 dBm, and the power gain is 13.22 dB.

Graphene based filter design using triangular patch resonator for THz applications

In this paper, graphene based tunable bandpass and bandstop filters are designed in terahertz frequency regime using a triangular microstrip patch resonator. Initially, a bandpass filter is designed at an operating frequency of 1.65 THz with a bandwidth of 65 GHz. Further a dual-band bandstop filter is designed with resonance frequencies of 1.25 THz and 2.14 THz. In both designs, the triangular patch is coupled to the transmission line to achieve bandpass and bandstop characteristics. A graphene layer is deposited between the dielectric and the conductor layer to enhance the propagation of plasmonic waves. The simulation results reveal that the designed filters are capable of achieving the desired frequency response. By varying the graphene’s chemical potential, a shift in the transmission response’s resonance frequency is observed. The proposed filters have the potential to be used as key components for future terahertz band communications systems.

On Six-Element Bridged-T RC Bandstop and Bandpass Networks

This paper is concerned with a six-element bridged-T RC network, which is a bandstop filter, but by reorientation, can also achieve bandpass characteristics. The general configuration is analyzed for its transfer function and then two special cases are considered. Interestingly, the bandstop configuration in one case and the bandpass configuration in both cases show over-unity gain in a small range of frequencies.

Demonstration of an Integrated terahertz band-stop filter using an apodized Bragg grating.

This paper presents the demonstration of an on-chip integrated terahertz (THz) apodized Bragg grating (TABG) which functions as band-stop filter with a center frequency of 0.8 THz and a bandwidth of 200 GHz. For experimentation, we integrate the TABG into our THz system-on-chip to enable wideband (DC - 1.5 THz) device characterization. Using this methodology, we measure the signal transmission through the TABG and find the experimental results align with simulation and theory provides a rejection of approximately 20 dB across the stop-band.

Nonvolatile tuning of Bragg structures using transparent phase-change materials

Bragg gratings offer high-performance filtering and routing of light on-chip through a periodic modulation of a waveguide’s effective refractive index. Here, we model and experimentally demonstrate the use of Sb2Se3, a nonvolatile and transparent phase-change material, to tune the resonance conditions in two devices which leverage periodic Bragg gratings—a stopband filter and Fabry-Perot cavity. Through simulations, we show that similar refractive indices between silicon and amorphous Sb2Se3 can be used to induce broadband transparency, while the crystalline state can enhance the index contrast in these Bragg devices. Our experimental results show the promise and limitations of this design approach and highlight specific fabrication challenges which need to be addressed in future implementations.

A new tunable bandstop filter square-ring resonator using varactor diodes.

This work presents the development of a bandstop filter with a tunable response. Varactor diodes are used as control elements. Studies and investigations demonstrate the influence of the variable capacitance on the input admittance and on the S-parameters frequency responses of the proposed square-ring resonator geometry. The design of the square-ring resonator is based on mathematical modeling of ideal transmission lines, considering parameters of characteristic admittance and electrical length for odd and even excitation modes. Based on S-parameters in ports, an equivalent circuit model of the resonator geometry is presented. The corresponding results are compared with numerical simulations. Comparative analyses are presented in order to guide the process of optimizing the physical dimensions of the layout. A prototype with dimension 0.0272 [Formula: see text] was designed, fabricated, and tested. As a measured result, a filter with two rejection bands was obtained, the first at 0.6-1.15 GHz and the second at 1.71-2.28 GHz, with 63.0 and 29.0% tuning range, respectively. In comparison with bandstop filters from the literature, the proposed reconfigurable filter presents a larger tuning range for the first band, sufficient inband rejection levels for several applications, and reduced physical dimensions. The proposed configuration is an attractive reconfigurable filtering device for use in modern communication systems operating below 3.0 GHz.

A Broad Stopband and High Rejection HTS Lowpass Filter for Quantum Computers

This paper presents a novel approach for extending the upper stopband of lowpass filters. The proposed technique involves dividing the hairpin unit cells' coupled lines into multiple smaller components, which shifts the harmonics to higher frequencies while maintaining the cut-off frequency. Additionally, the stopband is further extended by modifying the tapping position to suppress the second harmonic. For demonstration, an improved dual-hairpin unit cell is devised, which is able to extend the stopband up to 11.3 times the cut-off frequency. Furthermore, a cascaded lowpass filter utilizing multiple improved dual-hairpin unit cells is also designed, which is divided into two sub-filters to suppress enclosure resonance. The cascaded filter is fabricated on an HTS (high-temperature superconducting) thin film deposited on a MgO substrate, demonstrating a cut-off frequency of 483 MHz, extending the stopband to 25.1 GHz (51.9 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f_c</i> ), affording a rejection level exceeding 60 dB and insertion loss below 0.04 dB. Notably, the roll-off rate exceeds 569 dB/GHz, and the size measures only 0.144 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_g</i> × 0.030 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">λ_g</i> .

Design and analysis of tunable optical filter based on silicon-on-insulator photonic crystal for visible light communication

In this paper, tunable narrow bandwidth band-stop and band-pass optical filters for visible light communication (VLC) are designed and numerically investigated using a photonic crystal (PC) structure. Designing a tunable filter for visible light communication is crucial for enhancing spectral utilization and maximizing communication efficiency. A rectangular defect with optimized sides length utilized in the center of the PC structure based on the desired filtering characteristics. To obtain a favorable narrow bandwidth filter for visible light wavelengths, this defect is filled with a specific liquid crystal. In addition, an electric field is applied to the proposed structure in order to change the refractive index of the liquid crystal and achieve tunability in the desired range. The functional wavelength ranges of band-pass and band-stop filters are 550–570 nm and 565–585 nm, respectively. Applying an electric field causes a shift in the central wavelengths of the filters. It is shown that a 1.5 nm central wavelength shift for a band-stop filter and a 0.9 nm central wavelength shift for a band-pass filter can be achieved by changing the voltage source up to 1.5 V. In addition, the impact that the variation in the length of the rectangular defects’ sides has on the filtering characteristics of the proposed device is studied.

An ultrawideband antenna with two independently tunable notch bands

This paper presents a planar CPW-fed Ultrawideband (UWB) antenna with two independently tunable notch bands. The proposed design consists of a modified Rhombus-shaped monopole structure that is integrated with a dual band-stop filter based on hexagonal split ring resonators (HSRR). The antenna is capable of suppressing multiple frequency bands within ultrawideband range (3.1–11 GHz) such as WLAN and X-band downlink satellite communication frequency bands with an independent tunable mechanism to fulfill the on-demand band rejection. The frequency reconfigurability of the two notch bands is obtained by loading the hexagonal filter arms with two varactor diodes (for each band). Details of antenna design steps and reconfigurability mechanism are illustrated. The notch band element is explained using equivalent circuit model and surface current distribution at lower and higher notch frequency bands. A prototype of the proposed design is printed on the RO4003C (ϵr = 3.55) substrate printed circuit board (PCB) and tested to authenticate the performance. The proposed antenna volume is 21.5 ▪ 48 ▪ 1.524 mm3 and demonstrates an omnidirectional radiation pattern in E and H planes with an average gain of 3.7 dBi across the operational passbands, while a sharp reduction in gain of -6.8 dBi and -3.5 dBi is achieved at the lower and higher notch bands, respectively. Continuous tuning is achieved experimentally from 5.08 to 5.77 GHz and 7.75 to 8.52 GHz for the lower and higher notch bands, respectively. Excellent agreement is observed between the simulated and measured results. Application areas include radio-frequency identifications, ground-penetrating radar, and wireless communications.

Tunable bandstop filtering specialities in superconducting Thue–Morse photonic multilayers

We theoretically investigate wide and tunable bandstop filters based on one-dimensional superconducting photonic multilayers. These multilayers are composed of superconductors (Nb) and semiconductors (GaAs), arranged in accordance with the Thue–Morse sequence. The wide transmission bandgap of the multilayers can be utilized as a bandstop filter, with greater accuracy achieved by larger sequence number and thinner semiconductor. Our results demonstrate that both the bandwidth and center frequency decrease as the ambient temperature and semiconductor thickness increase. Especially, the stopband disappears when the temperature exceeds the critical temperature (Tc) of Nb. On the other hand, increasing hydrostatic pressure and superconductor thickness leads to monotonous increases in both the bandwidth and center frequency. Moreover, for thin superconductors or high temperatures close to Tc, the quality factor is high and tunable in a wide range. Our work presents a flexible solution for optical bandstop filters, which may also find potential applications in optical switching and modulating.

Design and Implementation of a Wilkinson Power Divider with Integrated Band Stop Filters Based on Parallel-coupled Lines

This paper presents a technique to improve the spurious suppression performance at the second harmonic (2f0) of a Wilkinson power divider. The technique is achieved by the insertion of bandstop filters realizing with parallel-coupled lines with the characteristic impedance of 2√Z0Ω and the electrical length of λ/8 in a conventional structure. The simulated and measured results of the conventional and the proposed divider are compared at 0.9 GHz. The insertion losses (S21, S31) are less than 3.1 dB, while the return losses (S11) are less than 34.6 dB across 100% fractional bandwidth. Moreover, the proposed Wilkinson power divider achieves more than 25.5 dB suppression at 2f0.

Second Harmonic Current Suppression and Dynamic Response Improvement for V2G System

Electric vehicles interconnect and interact with the grid bidirectionally through a vehicle-to-grid (V2G) system. In V2G, the output power on the AC side pulsates at twice the grid frequency 2 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> , which leads to the presence of a second harmonic current (SHC) on the DC side and reduces the reliability of the system. A bandstop filter (BSF) with a center frequency of 2 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sub> is introduced in the voltage sampling loop to suppress the SHC. A digital implementation of the BSF is proposed to apply at arbitrary frequencies, which avoids the cost increase and provides high simplicity and flexibility. An adaptive PI control method is further proposed to improve the dynamic performance, which adjusts the PI parameters in real-time according to the inductor current. A 3.5 kW V2G experimental prototype is built and tested to verify the feasibility and stability of the proposed strategies. The prototype offers an excellent dynamic and steady-state response in stand-alone and grid-tie modes.

Using Mixed Coupling to Realize Wide Stopband Multilayer Substrate Integrated Waveguide Filter

Mixed coupling has been used in substrate integrated waveguide (SIW) filters to eliminate the transmission of spurious modes. However, the elimination only applied to the first spurious mode. Here, we propose a new mixed coupling structure that consists of slots for magnetic coupling and holes for electric coupling. Using it as the inter-coupling structure, the total coupling/transmission of multiple spurious modes can be zero. This brief presents a prototype that is a multilayer SIW filter working in TE101 (f0). Theoretically, all the spurious modes below TE404 of this prototype can be eliminated efficiently, which is verified by an experiment result showing a stopband extended to 4.02 f0. The proposed technique not only extends the stopband of SIW filters but also the application scope of mixed coupling. It should facilitate the development of high-performance SIW filters in wireless/microwave circuits and systems.

Design of a Common-Mode Rejection Filter Using Dumbbell-Shaped Defected Ground Structures Based on Equivalent Circuit Models

An efficient design method is proposed for a compact common-mode rejection (CMR) filter utilizing dumbbell-shaped defected ground (DS-DG) structures and gap-coupled stub (GCS) resonators. A CMR filter for differential lines helps to improve the signal integrity of high-speed digital signals on printed circuit boards. The proposed CMR filter design is based on the equivalent circuit models, while the previous designs depended heavily on the DS-DG structure optimization using the EM simulations. The proposed CMR filter effectively rejects the common-mode components while minimally affecting the differential signals. To prove the simplified design approach, a fifth-order Chebyshev band-stop filter is designed with three DS-DG structures and two GCS resonators. From the simulated and measured results, it is found that the proposed CMR filter provides ~90% fractional frequency bandwidth with more than 20 dB of common-mode rejection ratio and less than 0.6 dB of insertion loss of the differential signal.