Showing papers on "Prototype filter published in 1969"

A step-by-step active-filter design

Abstract: This article presents, in a simplified manner, a design method for active filters intended for those who are not filter specialists. By following the described five-step approach, a circuit designer who has some knowledge of passive filters will (without having to learn a whole new technology) be able to design active filters just as easily as he now handles conventional passive filters. Starting with the filter specification, it is shown sequentially how to realize a network that meets the prescribed requirements. Configurations and element values are given for the low-pass (LP), bandpass (BP), high-pass (HP), all-pass (AP), and band-elimination (BE), second-order active filter building blocks.

The Stepped Digital Elliptic Filter

Abstract: The design and synthesis of various types of microwave elliptic function filters has been accomplished by a number of authors. However, one problem in this field which remains is the realization of compact narrow-band bandpass elliptic function filters. In this paper, a procedure is presented which enables this class of filters to be constricted in a compact digital form. Since the physical realization is in the form of an n-wire line, one-quarter of a wavelength Iong at the center frequency of the passband, where the impedance levels are stepped along the center of the coupled lines, the filter has been termed the stepped digital elliptic filter. The absence of awkward interconnections in the filter due to the stepped digital structure inherently implies that reasonable insertion loss characteristics may be achieved in the X-band region and above, and also simplifies the mechanical construction. It is shown that the resonant elements in the filter, due to the design procedure adopted, are relatively insensitive to the absolute bandwidth of the filter, and consequently fractional bandwidths of approximately 30 percent and below may be readily achieved while the normalized impedance values of the elements in the network remain of the order of unity. This latter result is similar to that obtainable from conventional interdigital filters but in the case of narrow bandwidths the stepped digital filter is considerably smaller in physical size. A systematic procedure is also formulated for the inclusion of the parasitic lumped end effect capacitances into the overall design procedure in order to maintain the equiripple passband and stopband responses. Experimental results are presented for a five-element, 11 percent bandwidth filter and are shown to be in good agreement with theoretical predictions.

Sharp-cutoff low-pass filters using floating gyrators

Abstract: The practical realization in gyrator-C form of a seventh-order Cauer-parameter low-pass filter with 40-dB stopband attenuation is described. The three floating coils of the equivalent LC filter were replaced by capacitor-loaded semi-floating gyrators. The gyrators were realized in hybrid form using thick-film resistors. The performance of the filter over a temperature range from -40/spl deg/ to +61/spl deg/C was very satisfactory, without any attempt at temperature compensation being made. This, together with the wider allowable element tolerances (compared with other active RC filter methods) shows the inherent suitability of gyrator-C filters for integration. Also in this paper some of the special problems and characteristics of gyrator-C filters are theoretically discussed, in particular the realization of gyrators with floating ports, gyrator Q-enhancement, and component tolerances in gyrator-C filters.

A Class of Time-Varying Digital Filters

Abstract: Discrete-time signals and digital filters have become increasingly important in recent years with the rapid advance of technology in integrated digital circuitry and the increasing availability of digital computers. This paper is concerned with a class of linear time-varying digital filters and the response of such filters with stochastic input signal. It is shown that these filters possess a number of useful properties; the most important of which is the preservation of wide-sense stationarity of stochastic inputs. Such properties can facilitate considerably the analysis of systems incorporating these filters. It is shown that this class is the most general class of time-varying filters that preserve the wide-sense stationarity of the inputs. A subclass of these filters is shown to be periodic and hence can be implemented simply by using parallel connection of time-invariant filters and a rotating switch. The response of these filters to periodic inputs is analyzed.

The Design and Synthesis of a Class of Microwave Bandpass Linear Phase Filters

Abstract: This paper is concerned with the design procedure and synthesis of a class of microwave bandpass linear phase filters which simultaneously exhibit a maximally flat amplitude and delay response about band center. In the first part of the paper a systematic procedure is developed for the construction of a nonminimum phase transfer function which exhibits a maximally flat delay and maximally flat amplitude characteristic. In the second part, a synthesis procedure is presented for the realization of the general nth-ordered transfer function by a generalized interdigital network. To simplify the design and construction of this filter, typical characteristics for filters of degree n = 3,4,5,6,7 are graphically presented together with a tabular representation of the polynomials which are required to design the filter. Finally, the results of an experimental filter of degree 3 are incorporated to illustrate that this class of nonminimum phase filters may readily be constructed in practice.

The Design of Optimal Convolutional Filters via Linear Programming

Abstract: Computational algorithms are given for the design of optimal, finite-length, convolutional filters with finite-length input sequences. Design techniques are developed for minimum-weighted-mean-square-error filters (MWMSE), for minimum-weighted-absolute-error filters (MWAE), and for filters which minimize the maximum output error (minimax). It is shown that the coefficients of the MWAE and minimax filters can be obtained by using standard linear programming methods. Next, the problem of developing a filter whose function is to "sharpen" a particular input waveform is considered. The filter input sequence is assumed to be derived from a Ricker wavelet of the velocity type and the desired output is the Dirac delta function. Convolutional filters are developed for this problem using each of the three performance criteria described above. The output sequences of each of the three optimal filters are discussed. It is shown that the minimax filter gives significantly better discrimination than can be obtained from either the MWAE or MWMSE filters.

Predistorted Waveguide Filters for Use in Communications Systems

Abstract: Predistortion is a standard technique for correcting the effects of energy dissipation in filters, making their response conform to that of ideal filters. The problem of dissipation is particularly noticeable in narrowband bandpass filters used in microwave communications systems. Dissipation makes the passband edges slump downward, as shown in Figure 1, which can cause distortion and intermodulation. In predistorting a filter, we allow for dissipation in the initial design. A response approximating the ideal response can be approximated at the price of increased insertion loss. The flat response of predistorted filters is advantageous when used in high-capacity microwave communications systems; however, the filters have an additional property which makes them especially attractive for certain applications in microwave communications systems.

Field Analysis of Helical Resonators with Constant-Bandwidth Filter Application

Abstract: The problem of designing helical resonators for use in constant-bandwidth tunable filters from VHF through UHF frequencies is approached from two different viewpoints and the conclusions are verified by experimental results.

General expression for the group delay of digital filters

Abstract: An expression for the group delay of a digital filter is derived in terms of the numerator and denominator polynomials of the transfer function H(z) The application of this expression to three cases is shown, and an important theorem relating to the exact realisability of linear phase digital filters is given

Wave-propagation analysis of the monolithic-crystal filter

Abstract: The monolithic-crystal filter has two or more pairs of electrodes on the same piezoelectric plate; mechanical-wave propagation in the regions between electrodes takes place in an evanescent mode. A method of analysis, based on solutions to the wave equation, is first developed in general terms and then applied specifically to AT-cut quartz. Boundary conditions are used to determine resonant frequencies and vibration patterns under short-circuit conditions; from these, the electrical equivalent circuit is developed. Experimental results confirm the validity of the method. The theoretical results presented describe the bandwidth and motional capacitances of 2- and 3-resonator filters as functions of their geometry (electrode width, thickness and spacing). A method of predicting unwanted resonances is developed. A 3-resonator filter, with a centre resonator of different geometry, is considered. Some results relevant to multiple-resonator filters (up to ten) are described. Extension of the theory to overtone-mode devices is also discussed.

Electronically tunable acousto-optic filter

Abstract: The paper reports experimental results on a new type of electronically tunable optical filter (1). The filter makes use of collinear acoustic-optic diffraction in an optically anisotropic media. By changing the driving acoustic frequency, the band of optical frequencies which the filter will pass may be changed. A LiNbO 3 acoustic-optic filter with a pass band approximately 2 A wide, which is tunable from 750 A to 5500 A by changing the acoustic frequency from 750 Mc to 1050 Mc, has been demonstrated. Peak transmission at band center is about 30 percent and average rejection outside the pass band is about 50 db.

Variable-bandwidth filters using switching

Abstract: It is shown that, if a switching technique is used to scale the bandwidth of a lowpass filter, the resultant circuit has some of the characteristics of an N-path filter. The consequence of this is that the signal frequency must be bandlimited to avoid spurious responses at the switching frequency and its harmonics.

Discrete-time filtering apparatus

Abstract: In a discrete-time filter, sensitivity to coefficient variation is substantially reduced by using a unit delay interval, for the delay networks of the filter, which is not equal to the sampling interval. Furthermore, in realizing higher order filter systems, a plurality of such filters may be cascaded, each having a delay interval different from that of the other filters. The periods of repetition of the poles of the overall filter function are therefore different, resulting in improved filter performance.

Narrow Bandwidth Elliptic-Function Filters

Abstract: Although wide bandwidth microwave elliptic-function filters have previously been reported, this paper describes a circuit which provides, for the first time, a narrow bandwidth elliptic-function response at microwave frequencies. It is for narrow bandwidth applications (from 5 percent to a fraction of a percent) that the elliptic-function filter offers its most important advantages over other filter types--lower loss and greater selectivity. These features are verified by theoretical analysis and experimental data on a 1-percent bandwidth S-band stripline filter. The design of the filter, which is based upon the low-pass prototype, is simple to obtain with the relationships presented in this paper, and the elliptic-function response is readily realizable in printed or other TEM transmission lines. A waveguide elliptic-function filter is also discussed, but experimental verification of this has not yet been attempted.

Bandstop filter for the H10 mode in a rectangular waveguide

Abstract: A bandstop filter for the H10 mode in a rectangular waveguide is established by a stub in the E-plane. The enlargement of the bandwdth of this filter by a stepped pattern of the stub or by cascading of stub filters is outlined.

Maximization of Signal-to-Noise Ratio in an Optical Filter

Abstract: where xeE , S = {xeE :0 0, (ii) B is symmetric and positive definite, (iii) # > 0. This problem arises in the maximization of the signal-to-noise ratio in a spectral filter for infrared detectors (see [7]). The term 2 represents the incoming signal and + ,B is the variance of the background signal. The constraint S reflects the fact that the filter can transmit no more than 100 % and not less than 0 % of the total energy. A paper detailing the physics of the problem is in preparation. Although various general-purpose algorithms have been developed which may be applied to obtain solutions to this problem, the special nature of the objective function and the constraints can be exploited to obtain more efficient solution techniques. Two related algorithms are presented here and are both based on a parametric analysis of the problem. The second method is based on the first and offers some computational advantages that the first does not possess. The derivation of the second method involves the notion of the "conjugate function" [6] in a unique manner and should be of interest in itself since the practical applications of this notion have heretofore been extremely limited.

Tailored response microwave filter

Abstract: A multiple section microwave filter capable of being accurately tailored to special frequency response requirements over wide bandwidths in disclosed. The tailored response filter consists of an array of cascaded traveling-wave directional filters. Each filter section couples power out of a through transmission line into suitable microwave terminations. Due to the directional characteristics of traveling-wave directional filters, there is no interaction between sections. Thus the frequency response of the array is the product of the transfer functions of the individual sections. The coupling constants and the center frequencies of individual filter sections are tailored, i.e., synthesized, to result in a set of individual transfer functions which will produce the desired overall response. The tailored response filter can be used in wide bandwidth microwave systems for phase and amplitude weighting and for equalization functions.

Synthesis of High-Power Harmonic Rejection Waveguide Filters

Abstract: Waveguide filters for rejection of harmonic power content of high-power transmitters are widely used, and corrugated waveguide or waffle-iron filters are most commonly employed for this application. The method of design described in the literature is based on the use of image parameters, and may be considered a rather complicated non-optimum procedure which may be difficult to control, particularly in regard to pass band VSWR, since empirical adjustments are usually required. The new methods described here are based on synthesis techniques, and give practical results close to the initial specifications. Only filters of the reflective type will be discussed, but occasionally conversion to the absorptive class is feasible.

Digital notch filters

Abstract: The letter deals with the special class of digital filters that possess a prescribed notch frequency. The present techniques for synthetising such filters rest on the bilinear-transformation method, where the designer is required to synthetise a continuous s plane notch filter, prewarp it, and then apply the transformation. It is shown here that notch filters can be synthetised directly into the z−1 plane.

Synthesis of Equally Terminated Low-Pass Lumped and Distributed Filters of Even Order (Correspondence)

Abstract: A Chebyshev-like polynomial of even order is described which, when used in low-pass filter design of even order, allows for the output to input resistance ratio of the filters to be specified independently of the passband ripple level. This is an improvement on the conventional theory, which requires that the resistance ratio be a junction of the passband ripple level. In particular, the important case of equally terminated lumped and distributed lowpass filters is considered in detail, and tables of element values are given for a large number of practical design specifications.

Vhf filter having absorptive tuned section to eliminate narrow spurious passband

Abstract: Disclosed is a very high frequency filter for use with a high frequency radio transmitter which prevents transmission of harmonics. The filter includes an absorptive filter which eliminates spurious passbands resulting from interaction of components. The absorptive filter includes highpass filters arranged in an L-network.

Tone channels for multifrequency receivers

Abstract: A tone channel of the type used in multifrequency receivers has in cascade an input band-pass filter that has a frequency curve similar to that of overcoupled filters, a limiter-amplifier, and an output band-pass filter that has narrow band-pass characteristics. The center frequency of both filters is the frequency of a desired incoming tone. After a signal ceases, ringing of the input filter caused by signal is at the peak response points of the input filter at either side of the center frequency, and it is therefore not effective to prolong ringing in the output filter.

Linear phase digital filter design

Abstract: The results of an investigation of linear phase digital filters are presented. It was determined that stable filters of this type are necessarily nonrecursive. The corresponding transfer function is presented in a general form in terms of basic z-plane pole and zero configurations. The design of digital filters of this form is accomplished by approximating a desired frequency function by one of four types of Fourier series. The types of series correspond to the forms of the z transfer function polynomial, which is either a mirror-image polynomial or a negative mirror-image polynomial, and either even or odd order.

Weight Selection in First-Order Linear Filters

Abstract: : The report describes methods for the proper design of first-order, recursive, fixed-weight, linear filters. Expressions are derived and listed for commonly used design parameters such as noise ratio, transient response, and truncation error. The performances of critically damped and steady-state optimum filters are compared. Design curves are given that can be used to select the weights of the steady-state optimum filter from total error requirements.

Band selection filter with two active elements

Abstract: The invention relates to active band-selection filters with a band-selection transfer function of the second order. The filter contains resistances and lossy resonant circuits. A significant feature for filter circuits constructed in accordance with the invention is that they contain two active elements connected in such a way that the denominator of the transfer function has certain well-defined symmetry properties related to the circuit parameters of the two active elements and to the passive elements. In filters with these symmetry properties changes in the transfer function caused by variations in the active and passive filter elements are minimized and the manufacture of band-selection filter is simplified.