Design Of Tunable Filter Research Articles

Design of tunable bandpass filter with an improved J-inverter

In this paper, a novel tunable bandpass filter with an improved J-inverter is suggested. In this resonator, as the loading capacitance is increased, the resonant frequency is decreased. Also, the phase of the admittance inverter has characteristics that are variable by series capacitors and parallel varactor diodes. The electrical length of the inverter always maintains 90° at a given physical length of the inverter, which should be changed for different operating frequencies. This new bandpass filter has a tuning range of 1.8 GHz ∼ 2.45 GHz and an insertion loss of less than 2.5 dB. Also, the bandwidth is almost constant within the tuning range. © 2012 Wiley Periodicals, Inc. Microwave Opt Technol Lett 55:852–855, 2013; View this article online at wileyonlinelibrary.com. DOI: 10.1002/mop.27467

Design and fabrication of independent-cavity FP tunable filter

This paper presents a novel micro-electromechanical systems (MEMS) FP tunable filter with a FP cavity independent of electro-static actuator, which is fabricated by the bulk micromachining processes. The electro-static actuator based on the parallel-plate capacitive actuation is separated with the FP cavity, and it can be designed without the limits to fabricate the FP cavity. The compatible MEMS fabrication processes with micromirror and FP cavity is proposed, in which the optical micromirror is fabricated with an average surface roughness (Ra) less than 6nm. The experimental results show that the fabricated FP tunable filter can be tuned 40nm with a driving voltage from 0V to 15V, its 3dB bandwidth is 0.4nm and the single mode fiber coupling loss is less than −3.7dB.

Dual-Band Bandpass Filter With Independently Tunable Center Frequencies and Bandwidths

This paper presents a novel approach to the design of tunable dual-band bandpass filter (BPF) with independently tunable passband center frequencies and bandwidths. The newly proposed dual-band filter principally comprises two dual-mode single band filters using common input/output lines. Each single BPF is realized using a varactor-loaded transmission-line dual-mode resonator. The proposed filter also offers switchable characteristics to select either of the passbands (either the first or the second passband only). To suppress the harmonics over a broad bandwidth, defected ground structures are used at input/output feeding lines without degrading the passbands characteristics. From the experimental results, it was found that the proposed filter exhibited the first passband center frequency tunable range from 1.48 to 1.8 GHz with a 3-dB fractional bandwidth (FBW) variation from 5.76% to 8.55% and the second passband center frequency tunable range from 2.40 to 2.88 GHz with the 3-dB FBW variation from 8.28% to 12.42%. The measured harmonic results of the proposed filters showed a rejection level of 19 dB, which is up to more than ten times of the highest center frequency of the first passband without degradation of the passbands.

Harmonic Suppressed Dual-Band Bandpass Filters With Tunable Passbands

This paper presents a novel approach to the design of tunable dual-band bandpass filter with broadband harmonic suppression characteristics. The proposed filter structure offers the possibility of two tunable passbands, as well as a fixed first passband and controllable second passband. The tunable passband frequency usually causes a shift of the harmonics, which need to be suppressed to improve out-of the passband characteristics. In order to suppress the harmonics over a broad bandwidth, defected ground structures are used at input and output feeding lines without degrading the passbands characteristics. Both theory and experiment are provided to validate the proposed filter. From the experimental results, it is found that the proposed filter exhibits a first passband center frequency tunable range of 34.14% from 0.85 to 1.2 GHz with the almost constant 3-dB fractional bandwidth (FBW) of 13% and second passband center frequency tunable range of 41.81% from 1.40 to 2.14 GHz with the 3-dB FBW of 11%. The measured results of the proposed filters show a rejection level of 20 dB up to more than ten times of second passband frequency can be obtained, thereby ensuring broad harmonics rejection characteristics without degradation of passbands. The measurement data have good agreement with the simulation.

A compact plasmonic tunable filter using elasto-optic effects

We report on the theoretical concept of the design of a compact plasmonic tunable filter made of a metal–dielectric–metal waveguide and using elasto-optic effects. The proposed device is designed in a nanoring resonator structure and numerically studied by means of 3D-FEM simulations. We obtained an optimized nanoring resonator that has a radius R=390nm and resonances at the telecommunication wavelength of 1.58μm. Simulations using elasto-optic material as the dielectric layer and top and bottom Ag layers as electrodes indicate that the output can be tuned in the telecommunication wavelength range with an applied field. Further, using the proposed device, optical switching phenomenon is also found to be possible. This tunable ring resonator filter with ultra-small radii is considered valuable for photonic integrated systems.

Design and fabrication of center frequency and bandwidth tunable HTS filter

We have developed a bandwidth and a center frequency tuning method for use in high-temperature superconducting microstrip filters. A pair of waveguide is placed between the resonators, and the bandwidth is adjusted by changing the switch states of the waveguides. Additional electrical pads are placed open ends of the resonators for tuning the center frequency. Pads are also placed around the input/output coupled-line elements to enable the external quality factors to be adjusted, thereby reducing the insertion loss caused by tuning. A prototype three-pole tunable bandpass filter was fabricated by depositing YBa2Cu3O7 thin film on an MgO substrate and has a measured center frequency of 4.83GHz and bandwidth of 121MHz. Use of the waveguides to adjust the coupling coefficients, the electrical pads to adjust the effective lengths of the resonators and the pads to adjust the external quality factors resulted in 120-MHz bandwidth tuning and 400-MHz center frequency tuning without increased insertion loss.

Power Handling of Electrostatic MEMS Evanescent-Mode (EVA) Tunable Bandpass Filters

This paper presents the first theoretical and experimental study on the power handling capabilities of electrostatically tunable MEMS cavity filters. The theoretical analysis indicates that the frequency-dependent RF voltage inside a narrowband filter may play an important role in the generation of electromechanical nonlinearities such as frequency response distortion, frequency shift, and bifurcation instability. This analysis also reveals that the filter's power handling capability is dependent on several critical factors, including the capacitive gap, stiffness of the diaphragm actuator, and the overall quality factor ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> ) of the evanescent-mode (EVA) resonators. A nonlinear computer-aided design (CAD) model is proposed as a practical tool for capturing the important tradeoffs in high-power design. An EVA tunable resonator and a two-pole 2% filter are fabricated and measured as vehicles to validate the theory and the CAD model. Specifically, a medium-power filter with a tuning range of 2.35-3.21 GHz (1.37:1) and an extracted unloaded quality factor ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Qu</i> ) of 356-405 shows measured power levels of 23.4 dBm (0.22 W) before bifurcation instability occurs. The measured IIP3 of this filter are 52.1 dBm. The theory and modeling, backed up by the measurements, provide significant insights into the high-power design of electrostatic tunable cavity filters.

Design and analysis of a novel noncollinear acousto-optic tunable filter

The design of a noncollinear acousto-optic tunable filter (AOTF) is commonly based on parallel tangent momentum-matching condition. Previous studies have either moving parts or modulation. These approaches would obviously decrease the accuracy of an acousto-optic tunable filter (AOTF) since it will be influenced by vibration or by an extended measurement time. In this paper, we introduce a novel noncollinear acousto-optic tunable filter division-of-amplitude photopolarimeter (DOAP). It is completely characterized by a wavelength-dependent 4×4 matrix that can be determined directly by calibration. The instrument has neither moving parts nor modulation. Besides, this system can acquire the image, spectral and polarization information of an object simultaneously.

Design of Tunable Bandpass Filters With Ferrite Sandwich Materials by Using a Piezoelectric Transducer

With their high relative permeability and high permittivity, magneto-dielectric materials show great potential in tunable bandpass filter designs. This paper presents a novel tunable bandpass filter with magneto-dielectric perturbation by using a piezoelectric transducer (PET) on a microstrip hairpin. Compared to traditional dielectric perturbation, the frequency tunability of the bandpass filter with magneto-dielectric is much larger while the insertion loss is not much affected. NiCo-ferrite films were adopted to laminate magneto-dielectric sandwich structure on a commercially available Rogers substrate. Novel bandpass filter designs with self-biased NiCo-ferrite films on one layer to five layers of the sandwich structure were compared and investigated. A maximum frequency shift of 240 MHz with respect to the unperturbed condition has been achieved.

Design of Tunable Flat-top Bandpass Filter Based on Two Long-period Fiber Gratings and Core Mode Blocker

We propose a tunable flat-top bandpass filter to pass light in a customized wavelength band by using long-period fiber gratings (LPFG) structure. The LPFG structure is composed of a core mode blocker in between two LPFGs. The bandpass spectrum of the proposed structure is obtained in overlapped wavelength band of two LPFGs operating on the same modes. To analyze the properties, we introduce a mathematical matrix model for the structure. We theoretically demonstrate flexibility of the flat-top bandpass filter with various bandwidths.

A tunable terahertz filter and its switching properties in terahertz region based on a defect mode of a metallic photonic crystal

We theoretically investigate and discuss an electrically tunable terahertz filter design and its optical switching properties based on the defect mode of a woodpile metallic photonic crystal (MPC). The model filter design is based on a dual use of an MPC as a resonator and as electrodes with a liquid crystal used as a defect layer. The static and the dynamic responses of a realistic liquid crystal are obtained using the Oseen–Frank elastic continuum theory, and the corresponding transmission spectra are calculated using an analytic modal expansion method combined with a transfer-matrix method. The tuning range of f = 1.430∼1.577 THz and the order of milliseconds switching property are observed in our design.

BOR-FDTD analysis of nonlinear Fiber Bragg grating and distributed Bragg resonator

Recently, nonlinear materials have attracted a great deal of attention because of their importance in designing new devices to meet a need range of optical systems. An intense investigation of the possibility of using these materials for all optical ultrafast applications is achieved by allowing their dielectric characteristics to be varied in such a way that a periodic perturbation of their refractive index along the length of the waveguide will be formed. The Finite-Difference Time-Domain (FDTD) method, on the other hand, has been proven to be one of the most powerful numerical techniques that are usefully applied to a wide range of optical devices. In this paper, a FDTD technique, developed for nonlinear structures, is used to analyze a nonlinear waveguide and periodic nonlinear structures that exhibit attractive properties that make them suitable for novel devices with wavelength tunable characteristics. More specifically, the Bodies of Revolution (BOR) FDTD numerical simulation method will be used to model the fiber Bragg Grating (FBG) and the direct integration method will be employed to include the effect of Self Phase Modulation (SPM) in this model. The combination of these techniques will result in a model that is used to analyze two different types of periodic nonlinear structure, FBG and Distributed Bragg Resonator (DBR). The nonlinear effect provides the designer an added degree of design flexibility for devices with wavelength tunable characteristics, for example, in the design of tunable filters, WDM systems and optical sensors.

Tunable active bandpass filter design

A tunable active bandpass filter that uses control voltage to select passband frequency response is presented. The proposed topology basically consists of a cascoded current-injection active inductor so as to tune passband frequency response from 2.35 to 3.66 GHz and extend the available bandwidth.

Tunable Bandpass and Bandstop Filters Based on Dual-Band Combline Structures

New methods for the design of tunable combline bandpass and bandstop filters are presented. The first part of this paper presents a tunable bandstop filter designed using a dual-band circuit with wide passband and integrated narrow stopband. A prototype has been constructed and measured results shows that the bandwidth remained constant at 30 MHz as the filter was tuned from 3.22 GHz to 3.66 GHz. The second part of this paper presents a tunable bandpass filter designed using a dual-band circuit with both wide passband and stopband. The response corresponds to two narrow passbands, where the lower passband bandwidth and center frequency can be tuned. A prototype has been constructed and measured results demonstrate wide centre frequency tuning range and over 300% bandwidth tuning without the need for coupling adjustment.

A Study on the Novel Rectangular Split Ring Notch Resonators

In this paper, a novel notch resonator is proposed based on Rectangular Split Ring Resonator (RRSS) element. We represented the electrical characteristics for R-SRR elements coupled with microstrip line, and measured result is compared with electromagnetic simulation (HFSS) result. We also solved equivalent circuit for R-SRR element, and also discussed influences of change structural parameters of R-SRR. The size of R-SRR is the most important parameters for frequency tuning. Also we can make tunable resonator form the basic structure. This novel resonator can apply to design of tunable bandpass filter and voltage control oscillator.

Inductively-loaded RF MEMS reconfigurable filters

This article presents an inductively loaded radio frequency (RF) microelectromechanical systems (MEMS) reconfigurable filter with spurious suppression implemented using packaged metal-contact switches. Both simulation and measurement results show a two-state, two-pole 5% filter with a tuning range of 17% from 1.06 GHz to 1.23 GHz, an insertion loss of 1.56–2.28 dB and return loss better than 13 dB over the tuning range. The spurious passband response in both states is suppressed below −20 dB. The unloaded Q of the filter changes from 127 to 75 as the filter is tuned from 1.06 GHz to 1.23 GHz. The design and full-wave simulation of a two-bit RF MEMS tunable filter with inductively loaded resonators and monolithic metal-contact MEMS switches is also presented to prove the capability of applying the inductive-loading technique to multibit reconfigurable filters. The simulation results for a two-bit reconfigurable filter show 2.5 times improvement in the tuning range compared with the two-state reconfigurable filter due to lower parasitics associated with monolithic metal-contact MEMS switches in the filter structure. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.

Design of tunable biquadratic filters employing CCCIIs: state variable block diagram approach

A state variable block diagram method is given for the realization of universal biquadratic transfer functions employing second-generation current-controlled conveyors (CCCIIs). Using minimum number of passive components and properly adjusting the bias currents of CCCIIs, the proposed circuits can realize all the tunable frequency standard filter functions: high-pass, band-pass, low-pass, notch-pass, and all-pass by choosing appropriate input branches without changing the passive elements. These presented circuits are in current-mode and voltage-mode separately. The non-ideality analyses of these configurations are given. Additionally, a high-order low-pass filter derived from the proposed voltage-mode biquadratic filter is introduced. PSPICE simulation results are included to verify the theory.

Design of bandwidth tunable HTS filter using H-shaped waveguides

We have developed a bandwidth tuning method for use in high-temperature superconducting (HTS) microstrip filters. Several H-shaped waveguides are placed between the resonators, and the bandwidth is adjusted by changing the switch states of the waveguides. The coupling coefficients between the resonators are controlled by switching the connection or isolation of the center gaps of the waveguides so as to tune the bandwidth. The effects of using this method were evaluated by simulation using a filter composed of 3-pole half-wavelength straight-line resonators with an H-shaped waveguide between each pair and additional electric pads for post-tuning trimming. The filter was designed to have a center frequency of 5 GHz and a bandwidth of 100 MHz by using an electromagnetic simulator based on the moment method. The simulation showed that bandwidth tuning of 150 MHz can be obtained by using H-shaped waveguides to adjust the coupling coefficients. It also showed that using additional electric pads around the feed lines, which was previously shown to be useful for trimming to improve insertion loss after center-frequency tuning, is also useful for bandwidth tuning.

Design of tunable terahertz photonic crystal narrow-band filters

The coupling between the line defect and point defect in a two-dimensional photonic crystal is studied by using plane wave expansion method and finite difference time domain method. Based on the analysis, we propose a novel tunable terahertz narrow-band filter. Simulation results on the defect modes and output spectra show that the photonic crystal that consists of two line defects and one point defect can act as a tunable filter with narrow bandwidth of 0.02 THz under the control of an external electric field.

Soft Error Rate Reduction Using Circuit Optimization and Transient Filter Insertion

This paper describes a tunable transient filter (TTF) design for soft error rate reduction in combinational logic circuits. TTFs can be inserted into combinational circuits to suppress propagated single-event transients (SETs) before they can be captured in latches or flip-flops. TTFs are tuned by adjusting the maximum width of the propagated SET that can be suppressed. A TTF requires 6–14 transistors, making it an attractive cost-effective option to reduce the soft error rate in combinational circuits. A global optimization approach based on geometric programming that integrates TTF insertion with dual-V DD and gate sizing is described. Simulation results for the 65 nm process technology indicate that a 17–48× reduction in the soft error rate can be achieved with this approach.