Showing papers on "Stopband published in 1997"

Theory and experiment of novel microstrip slow-wave open-loop resonator filters

Abstract: This paper presents the theory and experiment of a new class of microstrip slow-wave open-loop resonator filters. A comprehensive treatment of capacitively loaded transmission line resonator is described, which leads to the invention of microstrip slow-wave open-loop resonator. The utilization of microstrip slow-wave open-loop resonators allows various filter configurations including those of elliptic or quasi-elliptic function response to be realized. The filters are not only compact size due to the slow-wave effect, but also have a wider upper stopband resulting from the dispersion effect. These attractive features make the microstrip slow-wave open-loop resonator filters promising for mobile communications, superconducting and other applications. Two filter designs of this type are described in detail. The experimental results are demonstrated and discussed.

Existence of a photonic pseudogap for visible light in synthetic opals

Abstract: Synthetic opals, composed of submicron silica spheres close packed in a three-dimensional fcc lattice, are shown to display photonic stop bands at optical frequencies. We have investigated the light attenuation within the stop band as a function of refractive index contrast. Based on measurements of the Bragg attenuation length and on theoretical considerations, we show that a prominent depletion of the photonic density of states (pseudogap) can be achieved in opals by adjusting the volume packing fraction of the spheres and increasing the refractive index of the pores. To approach the pseudogap criterion the pores of opal were impregnated with CdS nanocrystals. We find a dramatic decrease of the attenuation length in opal-CdS, which indicates the strong perturbation of photonic states.

Enhancement of optical gain of semiconductors embedded in three-dimensional photonic crystals

Abstract: The three-dimensional photonic crystals used in this study were synthetic opals, composed of submicron silica spheres, close-packed in a face-centered cubic structure with a period of 200 nm, that exhibit photonic stopbands around 600 nm. We present measurements of the optical gain of CdS quantum dots (QDs) embedded inside the interstitials between the silica spheres. Unlike the usual gain spectra of CdS QDs in glass matrices, which display maximum gain at energies of the first quantum-confined transitions, for QDs embedded in photonic crystals the gain maximum is shifted toward the high-frequency edge of the photonic stopband (2.2 eV) far below the absorption edge of the semiconductor (2.5 eV). Studies of temperature, intensity, and orientation dependencies of the gain spectra allow one to ascribe the observed effect to gain enhancement caused by multiple coherent Bragg scattering of light in the periodic photonic crystal.

Filters and duplexers utilizing thin film stacked crystal filter structures and thin film bulk acoustic wave resonators

Abstract: There is provided a Bulk Acoustic Wave Resonator-Stacked Crystal Filter (BAWR-SCF) filtering circuit or device. The BAWR-SCF circuit comprises a first pair of ports, a second pair of ports, a first lead that is connected between a first and a second one of the first pair of ports, and a second lead that is connected between a first and a second one of the second pair of ports. The BAWR-SCF circuit also comprises a first BAW resonator connected in series in the first lead, and a second BAW resonator connected between the first and second leads. The BAWR-SCF further comprises a Stacked Crystal Filter (SCF) having first and second terminals connected in the first lead between the first BAW resonator and the second one of the first pair of ports. The SCF also has a third terminal that is connected to a node of the second lead. The frequency response of the BAWR-SCF circuit has steeply-sloped upper and lower edges that are similar to those yielded by ladder filters which are constructed primarily of BAW resonators. The upper and lower notches of the BAWR-SCF circuit's frequency response are also similar to those yielded by ladder filters which are constructed primarily of BAW resonators. The BAWR-SCF circuit also provides stopband attenuation characteristics that are similar to those yielded by SCFs. Additional BAW resonators connected in a ladder configuration and/or SCFs may also be provided in the BAWR-SCF circuit.

A simple design method for near-perfect-reconstruction nonuniform filter banks

Abstract: In this correspondence, we propose a simple design method for nonuniform integer-decimated filter banks based on a uniform cosine-modulated filter bank. The resulting distortion and aliasing are comparable to the stopband attenuation of the prototype filter. Examples are given to demonstrate the proposed method.

High-order micromechanical electronic filters

Abstract: Third-order, micromechanical bandpass filters comprised of three folded-beam resonators coupled by flexural mode springs are demonstrated using an IC-compatible, polysilicon surface-micromachining technology. The use of quarter-wavelength coupling beams attached to resonators at their folding-trusses is shown to suppress passband distortion due to finite-mass nonidealities, which become increasingly important on this micro-scale. A balanced, 300 kHz, prototype, three-resonator micromechanical filter is demonstrated with filter Q=590 and stopband rejection greater than 38 dB.

Design and realization of multiple quarter-wave phase-shifts UV-written bandpass filters in optical fibers

Abstract: Ultraviolet (UV)-written optical fiber bandpass filters based on multiple quarter-wave phase-shifts, up to eight, are presented and modeled. It is demonstrated that the shape of the bandpass peak can be tailored by optimization of the phase-shifts locations. We show that flat top bandpass peak with negligible ripples (<0.01 dB) at the top can be designed and that a tradeoff between nearly rectangular shape and stopband width occurs when gratings containing more than two phase-shifts are to be used. We also present experimental spectral responses of gratings with up to three phase-shifts and comparisons with theoretical results.

Fabrication and characterization of bandpass filters based on concatenated chirped fiber gratings

Abstract: Practical, low-loss ( 30 dB out-of-band rejection over /spl sim/25 mm spectral widths. The approach adopted is based on the concatenation of two or more tailored broadband chirped gratings fabricated with low short-wavelength loss to maximize the rejection and stopband width in a filter with /spl sim/1 nm passband. The effect of thermal aging for similar complex structures is considered in the context of three different fiber types: standard telecommunication, high germania (Ge)-doped and boron/germania (B/Ge)-codoped. It is shown that while hydrogenated B/Ge-codoped fiber exhibits excellent photosensitivity, the resulting decrease in guiding strength and thermal stability may make germania-doped fiber the more attractive choice.

Surface-acoustic-wave filters with poles of attenuation created by impedance circuits

Abstract: A surface-acoustic-wave filter couples a two-port surface-acoustic-wave resonator filter circuit coupled in parallel or in series with a two-port impedance circuit. The two-port impedance circuit has an impedance that creates a pole of attenuation, by making the open-circuit impedance of the surface-acoustic-wave filter equal to the short-circuit impedance. High attenuation over a wide range of stopband frequencies is obtained in this way, combined with steep roll-off between the passband and stopband.

Optimized E-plane bandpass filters with improved stopband performance

Abstract: A computer-aided synthesis technique for E-plane bandpass filters with improved stopband performance is developed. An optimization procedure based on equal ripple optimization is adopted. The design of a symmetrical E-plane bandpass filter with improved stopband performance is considered; higher order mode interaction between E-plane discontinuities is included in the design. The predicted filter performance shows improved stopband performance and reduced filter dimensions compared with conventional E-plane bandpass filters. The validity of the method is confirmed by the measurement of a fabricated five resonator E-plane bandpass filter with improved stopband performance.

A modified Chebyshev bandpass filter with attenuation poles in the stopband

Abstract: This paper describes a design method of a modified Chebyshev bandpass filter with attenuation poles in the stopband. The insertion of attenuation poles into resonators in the authors' bandpass-filter design is accomplished by connecting a lumped inductor or capacitor in series with a shunt-type coaxial transmission-line resonator. The inserted poles which are distributed over the stopband can be chosen such that the insertion loss of the filter has equiripple characteristic and maximum attenuation in the stopband with the given number of attenuation poles. The modified Chebyshev bandpass filter designed by this method can be effectively used in diplexer design.

Fabrication of multipassband moiré resonators in fibers by the dual-phase-mask exposure method.

Abstract: We report on the fabrication of in-fiber moire filters by dual exposure of a nondedicated chirped phase mask. This simple technique produces broadband filters whose structure depends only on an intermediate stretch between two identical UV exposures. We demonstrate moire filters with as many as four narrow passbands within a 2-nm stopband.

Microstrip slow-wave open-loop resonator filters

Abstract: Microstrip slow-wave open-loop resonators allow various filter configurations including those of elliptic or quasi-elliptic function response to be realised. The filters are not only compact in size due to the slow-wave effect, but also have a wider upper stopband resulting from the dispersion effects. These attractive features mean the microstrip slow-wave open-loop resonator filters hold promise for mobile communications, superconducting and other applications.

Design techniques for SAW filters using slanted finger interdigital transducers

Abstract: This paper describes useful design techniques for wide-band linear phase SAW filters using slanted finger interdigital transducers (SFITs): to increase stop band attenuation, to flatten the pass band response, and to draw SFIT patterns for photo-masks. In order to increase stop band attenuation, a withdrawal-weighted SFIT is employed. A combination of a withdrawal-weighted SFIT and an unweighted SFIT provides good stop band responses, even though the number of finger pairs is small. In order to achieve a desired amplitude response in the pass band, an aperture-weighting technique for divided channels of SFITs is presented. A design method for drawing SFIT patterns for photo-masks is also described. A linear-phase SAW filter using SFITs with a 50% fractional bandwidth is designed and fabricated on 128/spl deg/ y-x LiNbO/sub 3/. A sidelobe suppression of 40 dB and a 3 dB to 40 dB shape factor of 1.12 were realized. Good agreement between theoretical and experimental results is obtained.

Eigen design of quadrature mirror filters

Abstract: This work presents a method for the design of quadrature mirror filters. A new frequency weighted stopband energy function is introduced, which leads to considerable flexibility in the design process. Unlike other techniques which involve searches and nonlinear optimization, our formulation reduces the design equations to an eigenvector problem. Furthermore, the resulting filters are regular and have additional desirable properties for applications to pyramidal coding of images, which together with DPCM, PCM, vector quantization, or zero-tree wavelet coding schemes leads to high compression ratios.

Slot antennas on photonic band gap crystals

Abstract: The radiation patterns of a slot antenna placed on a photonic band gap crystal have been measured. We used a layer-by-layer photonic band gap crystal having a three-dimensional stop band between 12 and 15 GHz. The slot antenna radiation depends sensitively on the relative position and orientation of the slot in the surface unit cell of the photonic crystal. We have found configurations of the slot antenna with an increase of radiated power by 2-3 dB. The photonic band gap crystal can considerably improve the performance of a simple slot antenna.

Dual polarization frequency selective medium for diplexing two close bands at an incident angle

Abstract: A frequency selective medium that is adapted to receive an incident electromagnetic radiation at an angle of incidence of about 45° has two arrays of conductive elements on opposite parallel surfaces (20, 22) of a dielectric substrate. In one embodiment, the conductive elements are cross-dipoles (6) each having a horizontal dipole (10) and a vertical dipole (8) of different lengths and widths. In another embodiment, the conductive elements comprise a plurality of conductive gridded rectangular loops (40). The frequency selective medium allows incident waves that are within a passband of transmit frequencies to transmit through the medium, and reflects waves at frequencies within a stopband adjacent the passband. In other embodiments, meanderline polarizers (28) are added to cross-dipole and gridded rectangular loop frequency selective media to circularly or dual-linearly polarize incident linearly polarized waves.

High performance balanced type SAW filters in the range of 900 MHz and 1.9 GHz

Abstract: This paper describes balanced SAW filters with low insertion loss and high stopband rejection, which are applicable to 900 MHz and 1.9 GHz range portable telephone. The longitudinal coupled type double mode SAW design is suitable for balanced filter design. The 42 degree Y-X LiTaO/sub 3/ substrate is chosen to get low insertion loss and high Q factor performances. The design and evaluation method are studied and the effect of phase difference between balanced terminal signals is shown. The new filter design makes it possible to convert input/output impedance in order to match to an IC impedance.

Resonator-type surface-acoustic-wave ladder filter with improved upper stopband attenuation and reduced insertion loss

Abstract: In a resonator-type SAW filter, at least one series-arm SAW resonator has an interdigital transducer with reflectors on both sides, and the reflectors are separated from the interdigital transducer by a distance of from (N/2+0.55)λ 1 to (N/2+0.81)λ 1 , where N is an arbitrary non-negative integer and λ 1 is the wavelength of the surface acoustic waves excited by the SAW resonator. Alternatively, from 30% to 80% of the electrode fingers Constituting the interdigital transducer in at least one series-arm SAW resonator are apodized, dividing the interdigital transducer into an excitation region and a dummy region, and the electrode fingers in the dummy region are offset from the electrode fingers in the excitation region by a distance of 0.05λ 1 to 0.31λ 1 .

Exchange algorithms that complement the Parks-McClellan algorithm for linear-phase FIR filter design

Abstract: The authors describe an exchange algorithm for the frequency domain design of linear-phase FIR equiripple filters where the Chebyshev error in each band is specified. The algorithm is a hybrid of the algorithm of Hofstetter, Oppenheim and Siegel and the Parks-McClellan algorithm. The authors also describe a modification of the Parks-McClellan algorithm where either the passband or the stopband ripple size is specified and the other is minimized.

Position weighting of fiber bragg gratings for bandpass filtering

Abstract: A fiber Bragg grating bandpass filter with tailored refractive-index modulation is investigated. The writing method includes a position weighting technique, which provides flexible and accurate control of the index modulation along the fiber. This weighting is accomplished by adjusting the positions of a large number of overlapping subgratings to control the local grating strength. A 10-cm grating with a truncated sin(x)/x refractive-index modulation function was written and characterized with this method, showing good agreement with simulations. These types of filter are well suited for wavelength-division-multiplexing applications and can be made to have steep edges, low sidelobes, large bandwidth, and low stopband ripple.

Design of predictive IIR filters via feedback extension of FIR forward predictors

Abstract: Finite impulse response (FIR) predictors for polynomial signals and sinusoids are easy to design because of the available closed-form design formulae. On the other hand, those FIR predictors have two major drawbacks: the passband gain peak is usually greater than +3 dB, and a long FIR structure is needed to attain high attenuation in the stopband. Both of these characteristics cause severe problems, particularly in control instrumentation when the predictor operates inside a closed control loop. In this paper, we present a novel feedback extension scheme for FIR forward predictors. This extension makes it possible to easily design infinite impulse response (IIR) predictors with low passband ripple and high stopband attenuation. The new approach is illustrated with design examples.

Saw filter using low-pass configuration and method of providing the same

Abstract: An acoustic wave resonator filter (10) provides series and shunt resonator elements (22, 24) in a ladder network. The series elements (22) are configured in a lowpass configuration. The shunt elements (24) act as impedance inverters in a passband of the filter and they series resonate at an antiresonant frequency of the series elements (22) in a stopband which provides additional isolation. The electrodes (14) of the elements (22, 24) are of a metal thickness which improve the losses of a series resonant frequency in a passband which improves insertion loss. However, any increase in loss near the antiresonant frequency is compensated by the reduced loss near the resonant frequency of the shunt elements (24). The lowpass configuration and the aligned series element antiresonant frequency and shunt element resonant frequency provides good insertion loss, good isolation between transmitting and receiving bands, and maintains good stopband characteristics while reducing the number of elements required for the ladder network.

Optical bistability in colloidal crystals

Abstract: We present a one-dimensional model for the nonlinear response of a colloidal crystal to intense light illumination along a high symmetry direction. The strong coupling between light and the colloidal lattice, via the electric gradient force acting upon the particles, induces an interesting large optical nonlinearity. We obtain a bistable behavior when the incident frequency is inside the stopband of the periodic structure, with decreasing switching intensity as the frequency increases. The transmission characteristics and the magnitude of the switching threshold intensity are also in good agreement with a recent experiment. @S1063-651X~97!08703-5#

Rugate filter manufacturing by electron cyclotron resonance plasma-enhanced chemical vapor deposition of SiNx

Abstract: Electron cyclotron resonance plasma-enhanced chemical va- por deposition (ECR-PECVD) is used to deposit thin films of SiN x of different composition from mixtures of N2 and 30% SiH4 in Ar onto dif- ferent substrates. Measured values of the complex refractive index over the wavelength range of interest are used in the design and computer- controlled fabrication of one- and two-band rugate optical interference filters. The excursion of the continuously varying refractive index is cho- sen to be between 0.8 and 1.2, and window functions and matching layers at both sides are employed for sidelobe suppression. Measured reflection patterns of filters agreed well with simulated results. Filters designed for a center wavelength of 1000 nm and a total thickness of 2.1 mm, have a reflectance of 97% in the stopband and a bandwidth of typically 240 nm. The two-band filter is designed for stopbands at 1000 and 770 nm with reflectance of 98 and 96% and bandwidths of 150 and 120 nm, respectively. The total thickness of this filter is 3.33mm. Filters are successfully deposited on optical fiber ends using one of the fibers for in situ monitoring of the deposition process. © 1997 Society of Photo- Optical Instrumentation Engineers. (S0091-3286(97)04004-X)

Conductor loaded resonator filters with wide spurious-free stopbands

Abstract: A new configuration of conductor loaded resonator filters using two different size conductor loaded resonators and enclosures with significantly improved spurious performance Is presented. A rigorous mode-matching method is used to compute the resonant frequencies, unloaded Q, and the fields of the resonant modes of the conductor (solid or ring) loaded resonators. The coupling coefficients between two resonators are computed using small aperture coupling theory. The stopband characteristics of the filter are investigated. An eight-pole elliptic-function filter was designed, constructed, and tested. Extremely wide spurious-free stopband filter response was obtained which verified the theory.

SAW ring filters with insertion loss of 1 dB

Abstract: This paper presents low loss ring SAW filters on 49/spl deg/YX, 64/spl deg/YX, 128/spl deg/YX LiNbO/sub 3/ with reflective multistrip couplers (RMSCs). Using the RMSCs with 3 electrodes per /spl lambda/ (/spl lambda/ is the SAW wavelength at the center frequency) and the self-matching approach, when the static capacitance of the IDT is compensated by the acoustic radiation susceptance, the ring filters have shown very low insertion loss of 0.8-1 dB, 3-dB fractional bandwidth of 2-5% with very low ripple of 0.1 dB, stopband attenuation over 50 dB at 10-33% offset from the center frequency of 45 MHz. In a 50 ohm system, 148, 164, 172 MHz ring filters on 128/spl deg/YX for low power transceivers have provided an insertion loss of 1 dB, 1 dB bandwidth of 1.8-2 MHz, stopband attenuation over 55 dB at /spl plusmn/25 MHz offset from the center frequency. Two cascaded filters at 164.5 MHz have shown insertion losses below 3 dB and stopband attenuation over 90 dB at /spl plusmn/25 MHz, offset from the center frequency. The chip size is 5/spl times/4/spl times/0.7 mm.

Evanescent mode band reject filters and related methods

Abstract: Apparatus and related methods for an easily manufactured evanescent mode band reject filter that provides high performance with minimal dependence on critical dimensions. According to one embodiment, the present invention provides a band reject filter including a waveguide having an input, an output, a first wall between the input and the output, and a second wall opposite the first wall. The first wall is part of a substantially solid first block, and the second wall is part of a substantially solid second block. The waveguide is capable of transmitting an electromagnetic radiation signal from the input to the output, where the signal is at an operating frequency above a waveguide cutoff frequency. The band reject filter also includes at least one cavity coupled directly to the first wall of the waveguide, where the cavity is a substantially cylindrical cavity formed in the first block. Further, the cavity operates in an evanescent mode such that the cavity has a cavity cutoff frequency above the stopband frequency of the band reject filter. The cavity may have a circular, elliptical, or substantially rectangular cross-section in some specific embodiments.

Low-loss SAW filters using new SPUDT structures

Abstract: The new SPUDT structures based on triple electrode sections (TES) per wavelength with the period between SAW sources about n/spl lambda//3 are presented. The simulation technique which accounts for second order effects has been developed within the framework of modified equivalent circuit model. The SPUDT structures have been implemented in filters with 0.1-3.2% bandwidths fabricated on quartz and LiTaO/sub 3/ substrates. The results of simulation have been verified experimentally and show that insertion loss of TES SPUDT filters is less by 1.0-1.5 dB than that in conventional SPUDT filters. The impedance frequency dependence becomes more symmetrical and the passband distortions are reduced. Stopband rejection is 50-60 dB.

IEEE 1997 Ultrasonics Symposium Proceeding, pp.61-64, paper PT-3 LOW-LOSS SAW FILTERS USING NEW SPUDT STRUCTURES.

Abstract: The new SPUDT structures based on triple electrode sections (TES) per wavelength with the period between SAW sources about n/3 are presented. The simulation technique which accounts for second order effects has been developed within the framework of modified equivalent circuit model. The SPUDT structures have been implemented in filters with 0.1-3.2% bandwidths fabricated on quartz and LiTaO3 substrates. The results of simulation have been verified experimentally and show that insertion loss of TES SPUDT filters is less by 1.0-1.5 dB than that in conventional SPUDT filters. The impedance frequency dependence becomes more symmetrical and the passband distortions are reduced. Stopband rejection is 50-60 dB.