Showing papers on "Stopband published in 1990"

The static and dynamic characteristics of single and multiple phase-shifted DFB laser structures

Abstract: The influence of longitudinal mode spatial hole burning (LMSHB) on the performance of distributed feedback (DFB) laser structures is examined in detail. A comprehensive model has been used to interpret the experimental results and to construct a theoretical framework that was utilized to develop more advanced device designs. An increasing side mode intensity with output power, movement of the lasing mode relative to the stopband, and curvature of the light-current characteristic at low power can all be manifestations of the influence of LMSHB on the static device performance. The dynamic behavior can also be affected, with extended wavelength chirp and amplitude patterning effects on the timescale of the effective carrier recombination time being particularly important. >

Transverse resonance, standing wave, and resonator formulations of the ridge waveguide eigenvalue problem and its application to the design of E-plane finned waveguide filters

Abstract: An accurate computer-aided design of compact, low-cost, low-insertion-loss evanescent-mode waveguide bandpass filters with bilateral metallic E-plane fins is presented. The rigorous field distribution of the ridge waveguide eigenmodes is applied to the design. The design theory takes into account the influences of both the finite fin thickness and the higher-order mode interaction at all discontinuities. The numerical advantage of the transverse resonance method for solving the related cross-sectional eigenvalue problem is demonstrated for the design of quasi-high-pass and bandpass filters of different ridge gap widths and is compared with the classical standing wave and resonator mode-matching techniques. Computer-optimized design data are given for filters with passbands in X-band (8-12 GHz) and E-band (60-90 GHz), which achieve high skirt selectivity and wide stopband. The theory is verified by measurements. >

Asymmetric iris coupled cavity filters with stopband poles

Abstract: An improved type of asymmetric-iris coupled-cavity filters is introduced which utilizes the dual mode resonance and interference characteristics of the fundamental mode and the next-higher-order odd mode in suitably optimized resonators. This design achieves additional stopband poles which may advantageously be used to improve the edge steepness and the rejection characteristic in the second stopband. Based on the modal scattering matrix method. The rigorous design takes into account both the finite iris thickness and the higher-order mode interaction at all step discontinuities. Computer-optimized design examples of asymmetric inductive and resonant iris coupled resonator filters for the waveguide Ku-band (12-18 GHz) and W-band (75-110 GHz), respectively, demonstrate the improved stopband behavior. The theory is verified by available measured results. >

Periodic-structure photoexcitation of a silicon coplanar waveguide for selective optoelectronic microwave control

Abstract: Presented is a detailed analysis of the microwave Bragg-reflection characteristics of a periodically continuous-wave (CW) photoexcited coplanar waveguide on silicon substrate, with special regard to the inherent carrier diffusion mechanisms. In particular, the carrier diffusion in the direction of wave propagation can strongly affect the stopband reflection spectra of the configuration with respect to magnitude and bandwidth or with respect to efficiency and selectivity. The dominant effects are studied quantitatively and are outlined in the form of practical performance diagrams. Future application of periodically photoexcited transmission line sections for light-induced tunable filters or Bragg reflectors can be inferred. Initial experimental results from a three-section periodic structure of 17-GHz-center frequency under 840-nm light emitting diode (LED) CW excitation are reported. >

Microstrip lines using yttrium iron garnet film

Abstract: The spectral-domain technique is used to compute the dispersion characteristics and the transverse field distributions of microstrip lines using a yttrium-iron-garnet (YIG) film on a gadolinium-gallium-garnet (GGG) substrate. Numerical results are presented to show a sharp cutoff characteristic for a large thickness of GGG (which is caused by the reduction in the negative permeability range), and to show the effect of YIG film thickness on the nonreciprocal behavior. Experiments are carried out using YIG film a few tenths of a micrometer thick and a 400- mu m-thick GGG substrate. A narrow stopband characteristic of 200 MHz is observed at 6 GHz, which agrees well with theory. The application to a band-rejection filter is briefly discussed. >

Tunable, temperature-compensated dielectric resonators and filters

Abstract: A thermal and electromagnetic model of a tunable hybrid-mode dielectric double resonator is introduced and analyzed by the mode-matching technique. Results of the analysis show the temperature sensitivity of the structure as a function of the center frequency as well as the other resonator parameters. A simple optimization procedure which allows the design of the resonator to have both a wide tunability range and good thermal stability of the resonant frequency is described. A circuit model is presented for a tunable four-pole dual-mode filter. The model exhibits interesting dual passbands, separated by a very-high-attenuation stopband. Measured results obtained from an experimental four-pole dual-mode dielectric resonator filter designed using the tunable hybrid-mode resonators showed excellent tunability range (200 MHz at C-band) and good agreement with the circuit model. >

Filter system with controlled amplitude in stopband or passband

Abstract: A filter system which may be configured either as a stopband (notch) or passband filter having controlled gain and low ripple throughout its stopband or passband. The system includes a filter network which is operative for splitting an input signal spectrum into a pair of complimentary spectrum components and a coupler for proportionately combining these spectrum components in accordance with a prescribed gain factor. The filter network may either comprise a pair of complimentary band reject and band pass filters connected to a common input terminal or a diplexer including identical filters coupled between a splitter and a combiner.

Analysis of leaky-surface-wave propagating under periodic metal grating

Abstract: A detailed field analysis is presented for a leaky surface wave propagating under a periodic metal grating, using a theory that neglects the effect of mass loading due to the grating. The approach is based on Floquet's theorem and the coupled equations of wave motion with unperturbed mechanical and perturbed (or periodic) electrical boundary conditions, yielding a general field solution applicable to any material and to arbitrary connections to the grating. As a key step, the periodic boundary equations are solved by combining them into a set of infinite homogeneous equations through algebraic treatment and performing orthogonal integration with respect to space harmonics. The advantage in using this method results from there being no need to use assumptions or complicated expressions anticipating an accurate solution if sufficient space harmonics are considered. It is shown that the theory proposed here can be directly extended to solve simpler SAW problems. An analysis is carried out for LiNbO/sub 3/ for both the leaky wave and Rayleigh wave, taking into account dispersion relations, propagation attenuation of the leaky wave, and other field distributions. Theoretical and experimental results for the width of the first stopband are discussed. >

GHz low-loss SAW filters employing standard fabrication process

Abstract: The authors present SAW (surface acoustic wave) filter techniques suitable for low-loss operation. These techniques are based on a newly developed submicron photolithography as the appropriate mass-production low-cost pattern fabrication process. Two filters have been designed and realized at 1.7 GHz and 2.5 GHz, which corresponds to electrode widths of 0.6 mu m and 0.4 mu m, respectively. The filters provide an insertion loss of 6 dB and a stopband rejection of about 40 dB. The dual-track technique has been applied with the advantage of local separated structure parts responsible for low-loss operation and high selectivity. >

Coplanar waveguide discontinuities for p-i-n diode switches and filter applications

Abstract: A full-wave space-domain integral equation (SDIE) analysis of coplanar waveguide (CPW) two-port discontinuities is presented. An experimental setup to measure the S-parameters of such discontinuities is described. Experimental and theoretical results for CPW realizations of passband and stopband filters are presented. The S-parameters of such structures are plotted in the frequency range 5-25 GHz. >

New design techniques for SAW filters using slanted-finger IDTs

Abstract: The authors describe two design techniques for slanted-finger interdigital transducers (IDTs) which could not be designed using conventional techniques. One technique provides a large stopband attenuation: individual fingers or groups of slanted-fingers are withdrawn from the selected portions of the IDT. The other technique realizes a nonlinear phase response: the center-to-center distance between transmitting and receiving ITDs is varied along the axis normal to the surface acoustic wave (SAW) propagation axis. Two examples of filters, fabricated on x-112y LiTaO/sub 3/, are shown with about a 30% fractional bandwidth and a 19 MHz center frequency. One filter has a 45-dB stop-band attenuation, a 1.10 shape factor, and +or-0.05-dB passband ripples. The other filter has a nonlinear phase response which equalizes the phase response of an LC filter. This filter achieves a group delay distortion of less than +or-10 ns. >

Linear phase low pass filter

Abstract: An electrical signal filter composed of a pair of cascaded filter sections in which the group delays of the two filter sections are matched so that their non-linear effects cancel in the passband, resulting in an overall linear phase. In addition, the attenuation slope after the first null in one filter section's stopband response is complemented by the other filter's stopband attenuation. This prevents the overall stopband attenuation from falling to extremely low values as with some filters, which, in turn, limits the time domain overshoot. The passband group delay and stopband attenuation characteristics are controlled by appropriate selection of the passband ripple and filter order number parameters of the filter. In a preferred embodiment, the two filter sections are of the elliptic and Chebyschev type. The invention can be implemented as analog-component active filter circuit or as a digital filter.

Median-based feature selective filtering

Abstract: The design of a linear filter is quite straight forward especially if the spectra of the required and unwanted signals are known and do not overlap with each other. Basically, a linear filter is implemented by tuning its passband to the required signal and adjusting its stopband to the unwanted signal. However, in case of two or higher dimensional image filtering, we normally only have knowledge about the shape of the unwanted feature and have little or no knowledge about its spectrum. For non-linear filters such as the 2-D standard median filters, their filtering characteristics can only be roughly controlled by the size and the shape of the filter window. The unwanted feature cannot be specified in details and hence some related but required features may also be removed. In this paper, a novel median based feature selective filtering technique is introduced. Unwanted features of any particular shape can be specified in details by a set of custom-tailored shells and all features, other than those specified features which are to be removed, can be preserved regardless of feature orientations. In particular, this technique can be used to remove very high density impulsive noise from corrupted images.

A 900 MHz SAW microstrip antenna-duplexer for mobile radio

Abstract: A novel, 900-MHz SAW (surface acoustic wave) microstrip antenna-duplexer designed for use in European mobile radio systems is presented. The duplexer consists of a transmitter SAW filter, two receiver SAW filters, a low-noise receiver amplifier, and a duplexing microstrip circuit. A dual-track filter design using interdigital transducers for track coupling provides low insertion loss (5 dB), small passband ripple (+or-0.5 dB), high stopband rejection (50 dB), and small chip-size (TO-39 package). The filters were fabricated on 36 degrees -rotated YX-LiTaO/sub 3/ substrates with a photolithographic technique. Due to the design of the microstrip duplexer, the selectivity of the front end is enhanced by 15 dB. >

Prototype reference transfer function parameters in the discrete-time frequency transformations

Abstract: A direct discrete-time frequency transformation technique is presented with which it is possible to transform a prototype normalized lowpass reference transfer function into a denormalized lowpass (LP), highpass (HP), bandpass (BP), or bandstop (BS) transfer function. The salient feature of the proposed technique is that it permits prescribed values to be assigned not only to the passband edge(s) but also to the stopband edge(s) of the required denormalized transfer functions. In addition, it permits one degree of freedom in the determination of the passband edge and the stopband edge of the lowpass reference transfer function. This degree of freedom has been exploited to derive the passband edge and the stopband edge of the reference transfer function for the important class of denormalized LP, HZP, BP, and BS transfer functions with elliptic magnitude-frequency characteristics. >

An approximation algorithm for irregular-ripple filters

Abstract: A simple formulation is presented for the approximation of low-pass filters with specified number and level of ripples in the passband and stopband. The order of any finite attenuation or transmission zero can be specified as simple or double, and these zeros are not restricted to the jw axis. The method can be used to numerically obtain the characteristic functions of approximations ranging from the Butterworth to the elliptic ones. >

Sinusoidal and pulse responses of morphological filters

Abstract: The amplitude and phase responses of 1-D morphological filters to sinusoidal input signals are analyzed. The studied filters are dilation, erosion, opening, closing, and also open-closing and close-opening. The power spectral density of the filters is also analyzed for i.i.d. (independently identically distributed) Gaussian noise input. Rectangular pulse responses and root signals are discussed and responses to noisy edges are shown. It is shown that the opening filter has wider passband than the other morphological filters studied, and the open-closing filter behaves more consistently in the stopband than the corresponding median-based filters. The effect of the relative phase of the input signal is analyzed. The phase shift is found to change the amplitude response only at some discrete frequencies. >

Practical limitations in limiting the rate-line detectability of spread spectrum LPI signals

Abstract: Realizable filters (such as Butterworth, Chebyshev, and Bessel filters) were used to generate bandlimited symbol sequences so that practical limitations on symbol rate-line suppression could be investigated The signal-to-noise ratio at the output of a square-law detector, with the input matched to the symbol shape, was used as the measure of performance Analytical results were obtained for various filter orders The analytical results are compared with computer simulation results obtained using filters with finite impulse response It is shown that at low stopband attenuations ((20 dB), the Chebyshev symbol shape offered significant improvement in suppressing the rate line over the Butterworth or Bessel shapes, with the Bessel symbol shape being the worst of the three It is also shown that for large stopband attenuation, the performance differences between the filters became small >

IIR partial response digital filter design with equiripple stopband attenuation (class I)

Abstract: The design of infinite impulse response (IIR) digital transmitter and receiver filters of class I is described The filters are designed to be quasi-matched; each has a maximally flat delay polynomial as the denominator Each filter is designed to have an equiripple stopband attenuation as well as low, uncontrolled intersymbol interference (ISI) when cascaded In order to get low ISI and high stopband attenuation, it is necessary for the band-edge frequency to be slightly larger than the ideal value A brief comparison with finite impulse response filter design is made By IIR design, the filter order and group delay are reduced about 20% and 30% respectively, but the ISI is somewhat increased >

Filter and radio transmitter/receiver using it

Abstract: PURPOSE: To combine two filters without a circulator by providing plural open holes which extend from a top to a bottom and are arranged at a prescribed distance, selectively plating a dielectric means with electrically deductive material and separately forming a transmission line resonator to more than two open holes. CONSTITUTION: A block 210 has seven holes 201 to 207, and they extend from its top to its bottom. A plane securing the holes 201 to 207 is plated with electrically conductive material and each of them is a transmission line resonator which has a short circuit coaxial transmission lines 242 to 246 having selected length. A band-stop filter mechanism that is expressed with three zeros by the transmission line resonator in section A to C of the block 210 can acquire a level on which the degree of attenuation of a stop band in a flyback area is considerably increased. Thereby, the selectivity of a filter is not only increased, but also two of such filters can directly be combined without using a circulator.

Linear distortion compensation band stop filter

Abstract: PURPOSE:To eliminate a professional use signal band by arranging a plural-order of band stop filter, a high order delay equalizer compensating a delay distortion and a linear amplitude equalizer compensating the amplitude distortion of the pass band in cascade connection. CONSTITUTION:A plural order of band stop filter 5 having plural different attenuation poles of a detuning frequency required to obtain a desired attenuation of a stop band, a high order delay equalizer 6 compensating a delay distortion caused in the pass band of the band slop filter 5 by optimizing the filter effect with the least square successive approximation method maximizing the power separation ratio of a left channel of a stereo signal with respect to a right channel and a linear amplitude equalizer 7 compensating the amplitude distortion of the pass band caused by the band stop filter 5 and the delay equalizer 6 are arranged in cascade connection. Thus, the band for a professional signal is eliminated and the broadcast service for general home use applications is improved.

A courseware package for iterative design of FIR digital filters

Abstract: A computer algorithm written in BASIC is presented for the realization of a finite impulse response (FIR) digital filter designed using the Fourier series method. This method produces a linear-phase FIR filter of length L subject to an idealized geometry which assumes the passband is flat, the transition band is zero, and the stopband has infinite attenuation. The design technique allows the user to specify the minimum stopband attenuation (in dB). The resulting amplitude response is displayed on the terminal screen with the desired attenuation identified by a horizontal line throughout the stopband. The user either can modify L or insert/change the window function until the response is acceptable. The program is written for use with a personal computer and does not require a graphics board. The digital filter design package converts the Fourier series design algorithm from a hit-and-miss proposition to an iterative procedure which provides reasonable solutions. >

Rechteckhohlleiter-Filterstrukturen mit seitlich angekoppelten Resonatoren

Abstract: In this paper the analysis of a band-stop filter in waveguide technique is described. The filter consists of a rectangular waveguide with cavity resonators coupled to the broad or narrow side walls. It is possible to achieve not only the desired stop band but also the necessary pass band contemporary by appropriate design of the waveguide structure. The band-stop filter is interesting for use in transmitter and receiver sets, because of its low passband losses. The calculations are based on the field-theoretical exact procedures using a mode-matching method and the resonator method

Design method for optimal data transmission filters

Abstract: A data transmission filter design method is introduced. The method yields filters that are optimal in the sense that for given pole locations the intersymbol interference error is minimum. The prescribed loss requirements in the stopband are met and the eye diagrams are wide open.

Stopband characteristics of shallow gratings

Abstract: A numerical method of rapidly computing the width of the stopband of a shallow grating in a SAW filter and the dependence of this bandwidth on fabrication parameters is presented. The method is based on the properties of the equivalent circuit of the unit cell at the transition frequencies. Numerical results illustrate the variation of the relative bandwidth with respect to the element reflection coefficient, the mark-to-space ratio, and the velocity perturbation parameter. >

The Propagation Characteristics of Signal Lines with Crossing Strips in Multilayered Anisotropic Media

Abstract: In this paper, full modal analysis is used to study the dispersion characteristics of microstrip lines periodically loaded with crossing strips in a stratified uniaxially anisotropic medium. Dyadic Green's functions in the spectral domain for the multilayered medium in conjunction with the vector Fourier transform (VFT) are used to formulate a coupled set of vector integral equations for the current distribution on the signal line and the crossing strips. Galerkin's procedure is applied to derive the eigenvalue equation for the propagation constant. The effect of anisotropy for both open and shielded structures on the stopband properties is investigated.

An appbox.dution algorithy for iilbegulml-ripple filters

Abstract: A simple formulation is presented to the approximat ion of low- pass filters with specified number and level of ripples in the passband and stopband. The order of any finite attenuation or transmission zero can be specified as simple or double, and these zeros are not restricted to the jw axis. The method can be used to numerically obtain the characteristic functions of approximations ranging from the Butterworth to the elliptic ones.