Multiband Filter Research Articles

Design and characterization of MoO3/In2Se3 heterojunctions as terahertz/gigahertz band filters suitable for visible light communications and 3G/4G technologies

Herein, MoO3/In2Se3 (MI) heterojunctions are fabricated by a vacuum deposition technique for use as wideband filters. The MI devices are composed of optical and electrical parts to detect visible light spectra and microwave ac signals (0.01–3.0 GHz). Basic physical characterizations on the MI devices have shown that the devices are amorphous in nature, composed of MoO2.86/In2Se2.76 and exhibit valence and conduction band offsets of 1.62 eV and 3.10 eV, respectively. The optical conductivity analyses have shown that, the mobility and the plasmon frequency of charge carriers in the MI devices can reach 121.70 cm2 Vs−1 and 5.39 GHz, respectively. The terahertz cutoff frequency in these heterojunctions is in the range of 0.54–4.80 THz. On the other hand, application aimed characterizations has shown that the MI heterojunctions exhibit high photosensitivity against daylight light-emitting-diode irradiation. The capacitance-voltage characteristics tests have shown that MI devices can behave as metal-oxide-semiconductor field effect transistors (MOSFET). In addition, imposing ac signals of power of −1.0 dBm and measuring the power transmitted within a band width of 5.0 MHz in the frequency domain of 0.01–3.0 GHz indicated that the MI heterojunction devices can behave as multiband bandstop filters with notch frequency value that suits 3G/4G mobile technologies. The features of the currently proposed MI devices nominate them for use as optical receivers suitable for visible light communication technology, MOSFETs and as microwave band stop filters.

Tunable dual-band and high-quality-factor perfect absorption based on VO2-assisted metasurfaces.

Perfect absorbers with high quality factors (Q-factors) are of great practical significance for optical filtering and sensing. Moreover, tunable multiwavelength absorbers provide a multitude of possibilities for realizing multispectral light intensity manipulation and optical switches. In this study, we demonstrate the use of vanadium dioxide (VO2)-assisted metasurfaces for tunable dual-band and high-quality-factor perfect absorption in the mid-infrared region. In addition, we discuss the potential applications of these metasurfaces in reflective intensity manipulation and optical switching. The Q-factors of the dual-band perfect absorption in the proposed metasurfaces are greater than 1000, which can be attributed to the low radiative loss induced by the guided-mode resonances and low intrinsic loss from the constituent materials. By utilizing the insulator-metal transition in VO2, we further proved that a continuous tuning of the reflectance with a large modulation depth (31.8 dB) can be realized in the designed metasurface accompanied by a dual-channel switching effect. The proposed VO2-assisted metasurfaces have potential applications in dynamic and multifunctional optical devices, such as tunable multiband filters, mid-infrared biochemical sensors, optical switches, and optical modulators.

A quint mode fractal architecture based resonator and its efficacy in the design of multiband bandpass filters

This paper presents a new approach to design multiband bandpass filters (BPF) using multimode resonator topology inspired from Bamileke fractal architecture in the form of fractal shaped resonator. The proposed resonator architecture exhibits quint mode resonance behavior where resonance frequencies are determined using ABCD matrix. It offers flexibility in terms of choosing passband center frequencies precisely. Initially a second order dual band BPF is presented by suppressing higher order modes using asymmetric feed line. The same structure is used further to implement a triband and a quad band BPF where the input/output coupling circuit is modified to extract the higher order modes. Two stub loaded resonators are also embedded to improve the passband selectivity and to improve upper stopband characteristics. The design guidelines are demonstrated through the external quality factor (Qe) and coupling coefficient (k) synthesis approach. The developed filters are fabricated and measured to verify the predicted and simulated results. A close agreement is observed between them. The fabricated multiband BPFs has a very compact size, less insertion loss and good return loss profile.

Direct Synthesis of Multiband Bandpass Filters With Generalized Frequency Transformation Methods

This article presents a new generalized direct synthesis method to design multiband bandpass filters (MBPFs). Based on the proposed frequency transformation technique, it can be used to synthesize an arbitrary number of bandpass filters starting from a low-pass prototype filter. This synthesis allows determining analytically all the resonant angular frequencies and slope parameters of all the bandpass filters from the low and high cut-off angular frequencies used as initial specifications whatever the number of bands. To validate our method, triple-, quad-, and quint-band third-order Chebyshev bandpass filters are designed and implemented in microstrip technologies. Very good agreements were achieved between simulation responses and measurements.

Reflective coupled microring resonators for reconfigurable photonic systems: Performance analysis

We propose reflective type triple coupled microring resonators (TCMMRs) for reconfigurable photonic based systems. We have developed an analytical model and analyzed its useful performance characteristics. The TCMMRs based device exhibits a wide range of performance characteristics such as multi-band filtering, optical logical operations, and optical true-time delay lines. Reconfigurable multiple resonances and their splitting features associated with the device provide useful filtering performance characteristics such as high out-of-band rejection, flat-top bandwidth, and near to ideal shape factor. The device can perform multiple functions such as bandpass, bandstop, and notch filtering with a good performance. Unlike two input narrowband logical operations demonstrated in the literature, our proposed device can perform as three-input optical logical operator, and it can switch wideband microwave frequency signals optically. Moreover, the device exhibits wideband flat top group delay response. It carries out delay tuning using a single variable coupling coefficient which simplifies the complexity of the tuning encountered in binary tree-structured optical beamforming networks based on conventional microring resonators.

Spoof surface plasmon polariton beam splitters integrated with broadband rejection filtering function

In this paper, a new kind of spoof surface plasmon polariton (SSPP) beam splitter integrated with band-rejection filtering functions is presented. Firstly, the mechanism of single-band rejection phenomena of the SSPP transmission lines (TLs) with and without T-shaped decorations are revealed through dispersion analyses. Based on the single-band rejection filter, multi-band rejection filters are further designed by introducing different intervals between the symmetric T-shaped decorations. Furthermore, we construct a compact Y-shaped beam splitter integrated with a broadband band-rejection filtering function using the SSPP TLs, which consists of an SSPP TL with rectangular grooves and two filtering branch SSPP TLs. Multiple band-rejection integrated beam splitters can also be realized by incorporating different intervals between the T-shaped decorations. The integration of the SSPP beam splitter and band-rejection filter offers compact areas, lower insertion loss and controllable passband features. It is strongly believed that that the proposed idea will raise promising possibilities in the integration of multiple microwave functions in the same component, e.g. filtering antennas, filtering switches, multifunctional radiofrequency (RF) passive and active components capable of performing several RF analog signal-processing functions in the same circuit volume, and so on.

A New Class of High-Overtone Bulk Acoustic Resonators Using Lithium Niobate on Conductive Silicon Carbide

This letter presents a new class of High-overtone Bulk Acoustic Resonators (HBARs) with only top electrodes but excellent performance using lithium niobate (LN) thin films on conductive silicon carbide (SiC). The 4-inch single-crystalline lithium niobate thin film on conductive SiC (LNCSiC) substrate was prepared by ion-cutting process. Since the conductive SiC serves as both the resonant cavity and the floating electrode, the HBARs based on LNCSiC with only top electrodes were designed and fabricated. The devices show a wide frequency response span exceeding 2.0 GHz, a frequency spacing of 10 MHz, an excellent f $\cdot $ Q $_{\textit {LAKIN}}$ product of ${9.6}\times {10} ^{{13}}$ Hz ( f $\cdot $ Bode-Q of ${1.1}\times {10} ^{{14}}$ Hz), and a low temperature coefficient of frequency (TCF) of −18.9 ppm/°C. The frequency response shift of the proposed HBAR can be achieved by just adjusting the in-plane orientation of the top electrodes. Additionally, a multi-band filter was numerically synthesized based on the proposed HBARs, showing a spectral spacing of 10 MHz and a passband span of more than 2.0 GHz. Upon further optimizations, the proposed HBARs with a wide frequency response, a high- f $\cdot $ Q , and a low-TCF will be very promising for radio-frequency applications.

Dual-function tuneable asymmetric transmission and polarization converter in terahertz region

We theoretically demonstrated a switchable, as well as tuneable, asymmetric transmission and reflective polarization conversion device in terahertz region. The proposed dual-function device composed of vanadium dioxide (VO2) and Dirac semimetal (DSM) metamaterials (MMs). Switching is achieved by exploiting the dielectric-to-metal phase transition of VO2 board. On the one hand, the hybrid MMs structure behave as a transmission device when VO2 board in its insulating phase and VO2 grating in its metallic phase. In this case, broadband asymmetric transmission of linear polarization has been realised in the range of 2.023–5.971 THz. On the other hand, this hybrid metamaterial acts as a reflective device when VO2 board in its metallic phase and VO2 grating in its insulating phase. In this situation, linear-to-circular polarization conversion has been achieved in the ranges 2.058–3.423 and 4.753–5.6 THz, and at 6.496 THz. In each of the above working modes, tuneable spectral response has been achieved by modifying the Fermi energy of DSM materials. The device also exhibits a robust polarization conversion performance with the incident angle less than 40°. Dual-function metamaterial like the one presented here may find applications in active polarization controller, asymmetric transmission device, broadband and multiband filters, and other tuneable modulators.

Filter Realization of the Time-Domain Average Denoising Method for a Mechanical Signal

Time-domain averaging (TDA) is an effective signal processing technique in fault diagnosis that can extract the periodic components of interest from signals mixed with noise interference while suppressing other irrelevant periodic signals. However, there are two obvious shortcomings to TDA: first, the acquisition of keyphasor signals is often restricted by the application environment and conditions. Even if the signal is obtained by TDA, owing to the existence of periodic truncation errors, satisfactory results cannot be obtained. Second, due to the velocity fluctuation, the actual mechanical signal is easy to produce a large error in TDA stacking. To solve the above challenges, first, based on the disadvantage of using traditional resampling to solve the TDA synchronization problem, this paper proposes a new method of subsection resampling, which improves the analysis effect of the traditional TDA. Second, to further expand the range of the practical applications, according to the amplitude-frequency map of TDA, a method for realizing TDA function by using the FIR multiband filter is proposed. This approach effectively avoids the requirement of traditional methods to collect the keyphasor signals and broadens the application in practical engineering. Finally, the improved TDA method is compared with the filter implementation technology, and their respective application conditions are given.

Dual-frequency optoelectronic oscillator incorporating a single cavity and multiband microwave photonic filter.

Dual-frequency optoelectronic oscillators (OEOs) have potential applications in dual-band wireless networking and dual-parameter sensing systems. We propose a dual-frequency OEO incorporating a multiband microwave photonic filter (MPF). In particular, the two microwave signals are generated simultaneously in a single OEO cavity. By simply varying the parameters of optical spectral slicing and sampling (e.g., with a programmable optical filter) used to implement the MPF, we can readily achieve simultaneous tuning of the dual-frequency output, as well as alternate switching between single-frequency and dual-frequency output. The multi-passband nature of the MPF, enabled via optical spectral slicing, opens a path to multi-frequency OEO operation by scaling our scheme in the future. Such a structure provides a flexible way to generate simultaneously tunable and reconfigurable multi-frequency microwave signals.

Projective view at optimization problem for multiband filter

The best uniform rational approximation of the \emph{sign} function on two intervals separated by zero was explicitly solved by E.I. Zolotarev in 1877. This optimization problem is the initial step in the staircase of the so called approximation problems for multiband filters which are of great importance for electrical engineering. We show that known in the literature optimality criterion for this problem may be contradictory since it does not take into account the projective invariance of the problem. We propose a new consistently projective formulation of this problem and give a constructive optimality criterion for it.

Design and modeling of double Panda-microring resonator as multi-band optical filter

In this paper, the behavior of light within a double stage developed add-drop ring resonator called a double Vernier Panda-ring resonator (DVPR) is investigated using the signal flow graph technique in the Z-domain and Mason’s gain rule. The system included a double stage of add-drop ring resonators that each add-drop ring is attached to two small lateral resonators. The light transmission through the DVPR system is studied and the system responses analyzed in terms of the fundamental physical properties such as the free spectral range (FSR), structural dispersion, group delay, finesse, Q-factor and resonant bandwidth. Based on the coupling strength between the add-drop rings and the small lateral resonators (indirect couplers), different values of extended FSR from 64 nm to 90 nm were realized in the wavelength region of 1.4–1.7μm. Results analyzed for four values of indirect coupling strengths and the optimum layout was determined, which led to realize of a FWHM as narrow as 0.47 nm, the extended FSR of 81 nm for the center wavelength of 1535 nm, the structural dispersion of 6.0 fs/pm and a group delay of 3.9 ps. The superiority of DVPR design rather than the conventional Vernier ring-based filter is in achieving several values for extended FSRs, which provides different optical communication channels. These characteristics of our proposed structure ensure the tuning of optical communication channels by means of an optical device, which is desirable in the optical communication networks

Folded Substrate Integrated Waveguide Based Multiband Filter for Wi-Fi6E Application

This paper presents the design and development of a multiband filter using folded substrate integrated waveguide (FSIW) for the Wi-Fi 6E application. The emerging network standard IEEE802.11ax also known as Wi-Fi 6E is the next generation of Wi-Fi, which includes an additional frequency band at 6 GHz and provides improvements over 802.11ac (Wi-Fi 5). The designed filter is based on modification of the impedance of the FSIW structure introducing longitudinal as well as transverse slots. The equivalent circuit of the slot loaded structure is derived and simulated results using ADS are compared with the simulated results of the structure using HFSS as well as with the measured results. The measured results and simulated results using HFSS and ADS show the good agreement. The size of the designed structure is 0.31λg × 0.15λg and shows insertion loss less than 0.8 dB over the desired frequency bands.

Dual‐Sensitivity Terahertz Metasensor Based on Lattice–Toroidal‐Coupled Resonance

High quality factor resonance with extremely narrow line‐width offers an important platform for terahertz (THz) sensing technology as it enables strong light‐matter interaction between THz waves and analyte materials. Lattice mode arising from the collective Rayleigh scattering of metamaterial periodic structures has the ability to strongly confine the electromagnetic waves on the surface that fails to radiate to the far‐field. Herein, for the first time, a strategy is experimentally demonstrated to design THz metasensors, which exhibit dual‐sensitivity of frequency and resonance intensity by coupling the first‐order lattice mode to the toroidal resonance. The frequency sensitivity mainly results from the localized field confinement, whereas the sensitivity of resonance intensity depends on the matching degree between toroidal resonance and lattice mode. It is found that both the frequency shift and resonance intensity show exponential growth with the increase in the analyte thickness. In addition, the sensing performance between toroidal and toroidal–lattice modes is compared to verify the superiority of the dual‐sensitivity property. This work would greatly improve the practical applications of THz sensing technology and open up new opportunities for the realization of slow light devices, multiband narrow filters, and nonlinear systems.

Effect of the defected microstrip structure shapes on the performance of dual-band bandpass filter for wireless communications

Due to the progression growth of multiservice wireless communication systems in a single device, multiband bandpass filter has attract a great attention to the end user. Therefore, multiband bandpass filter is a crucial component in the multiband transceivers systems which can support multiple services in one device. This paper presents a design of dual-band bandpass filter at 2.4 GHz and 3.5 GHz for WLAN and WiMAX applications. Firstly, the wideband bandpass filter is designed at a center frequency of 3 GHz based on quarter-wavelength short circuited stub. Three types of defected microstrip structure (DMS) are implemented to produce a wide notch band, which are T-inversed shape, C-shape, and U- Shape. Based on the performance comparisons, U-shaped DMS is selected to be integrated with the bandpass filter. The designed filter achieved two passbands centered at 2.51 GHz and 3.59 GHz with 3 dB bandwidth of 15.94 % and 15.86 %. The proposed design is very useful for wireless communication systems and its applications such as WLAN and WiMAX

Tunable Plasmon-Induced-Transparency Effect in a Simple Planar Composite Structure

A planar metamaterial structure has been designed to obtain surface plasmon-induced-transparency (PIT) effect, which is composed of a nanodisk sandwiched between double rods. From theoretical perspective, the three-level plasmonic system has been utilized to analyze the near-field coupling mechanism. Besides, the simulation results show that PIT resonance can be tailored by structure parameters. Particularly, when the length of the rods is more than twice of the diameter of the disk, two PIT windows are generated simultaneously, based on the coupling between the bright mode of the nanodisk and two multipole dark modes of rods. Furthermore, a metamaterial structure, composed by a disk and two pairs of nanorods, is suggested to achieve the polarization-independent plasmon-induced-transparency effect. As a result, this work shows great application prospect in the area of compact optical devices, such as multiband tunable filters, plasmonic switches, and slow light devices.

Waveguide Components Based on Multiple-Mode Resonators: Advances in Microwave Multiple-Mode Waveguide Components, Including Multiplexers, Three-State Diplexers, Crossovers, and Balanced/Unbalanced Elements

Waveguide components have been widely explored for several decades, due to their inherent merits of low insertion losses, high quality (<;i>Q<;/i>) factors, and a significant power-handling capacity. Historically, cavity-based narrowband filters and multiplexers have been explored and designed for base stations and satellite applications. Compared with using single-mode resonators (SMRs), the implementation of multiple-mode resonators (MMRs) in waveguide structures is a promising solution to dramatically reduce the circuit volume and improve the frequency selectivity. Taking advantage of MMR techniques, various innovative waveguide structures have been proposed for a wide range of application scenarios. This article presents an overview of advances in microwave multiple-mode waveguide components, including narrow-, wide-, and multiband filters; multiplexers; three-state diplexers; crossovers; and balanced/unbalanced elements. Representative examples and their results are comprehensively discussed and summarized.

Ultraviolet Imaging Telescope (UVIT) observation of the Galactic globular cluster NGC 7492

ABSTRACT We present detailed photometric observations of the Galactic globular cluster NGC 7492 using the data obtained with two far-ultraviolet (FUV; 1300–1800 Å) and three near-ultraviolet (NUV; 2000–3000 Å) filters of Ultraviolet Imaging Telescope (UVIT) onboard the AstroSat satellite. We confirmed the cluster membership of the extracted sources using Gaia data release 2 (Gaia DR2) proper motion data. We have used colour–magnitude diagrams (CMDs) using UVIT and GAIA filters to separate out different evolutionary stages of the stars present in the cluster. We have identified a new extreme horizontal branch (EHB) star at the core of the cluster using UV and UV-optical CMDs. The estimated distance modulus of the cluster is 16.95 ± 0.05 obtained by fitting BaSTI isochrones with cluster parameters, [Fe/H] = −1.8 dex and age =12.0 Gyr on the V − I versus V CMD. Interestingly, only the EHB star and blue horizontal branch stars (BHBs) among the UV-bright hot sources are detected in FUV filters of UVIT. We have derived the effective temperature of BHBs using colour–temperature relation and spectral energy distributions (SEDs) of multiband filters, which are in the range from 8000 to 10 500 K. We find a variation of He abundance of BHBs by fitting the BaSTI ZAHB (zero-age horizontal branch). The range in the He abundance of the BHBs corresponding to the best-fitting isochrones is from 0.247 to 0.350. We have estimated various physical parameters of the newly identified EHB star in the cluster using SED fit and post-HB evolutionary tracks. We have studied the radial distribution of all the sources of the cluster detected in UVIT. The sources detected in FUV filters extend beyond the half-light radius (1.15 arcmin) of the cluster, whereas the sources detected in NUV filters extend beyond the tidal radius (9.2 arcmin) of the cluster.

An adaptive multi band-pass filter algorithm and its application in fault diagnosis of rolling bearing

Construction of an optimal band-pass filter for effective envelope demodulation spectral (EDS) analysis of rolling element bearing has been studied widely and amount of methods have been arising. However, most of these methods only get the envelope demodulation analysis result of a specific frequency band. In fact, multiple resonance bands might be caused when rolling bearing fails, especially when compound fault arises, and some key components buried in the original signal are often neglected by the above methods such as fast Kurtogram and Autogram algorithms. Therefore, it is particularly necessary to establish a multi-band pass filter algorithm for EDS. In the paper, an adaptive multi-band pass filter method based on signal energy is proposed, and then the square wave envelope analysis method is used for multi-band pass filtered signal to extract the fault characteristic frequency of rolling bearing. In addition, since the phase of the signal retains a lot of useful information of the original signal, the phase information of the multi-band filtered signal is retained and used for signal reconstruction. Not only the early weak fault feature could be extracted, but also the compound fault feature of rolling bearing could also be extracted by the proposed method, which is verified thorough simulation and experiments.

Compact Octa-band Bandpass Filter based on Controllable Transmission Zeros with Wide Upper Stopband

A novel synthesis method is proposed to design multi-band bandpass filters (BPFs) using an L-C ladder prototype lowpass filter loaded with two symmetric shorted stubs. The transmission zeros (TZs) are produced by the shorted stubs, which are used to realize multiple passbands. By controlling the number of the open stubs loaded on the shorted stub, the number of TZs is exactly determined. Therefore, multi-band BPF is easy to be obtained by increasing the number of the open stubs. The TZs can be adjusted by optimizing the L-C values of the equivalent circuit of the proposed filter to tune the center frequencies of each passband independently. The proposed BPF also has wide upper stopband. For demonstration, an octa-band BPF is designed and manufactured. The measured results show good agreement with the simulated ones.