Desired Filter Response Research Articles

Pseudoelliptic Waveguide Filters Using U-Shaped Ridge Resonators

A new structure for the realization of inline waveguide pseudoelliptic filters using U-shaped ridge resonators has been presented. The basic structure is a U-shaped ridge placed inside a rectangular waveguide and can be utilized to realize both a pole and a transmission zero by either adjusting its offset from the waveguide center axis or by making the lengths of its two arms different from each other. The dominant mode of the feeding waveguide acting as the nonresonating mode, bypasses the U-shaped ridge and thus creates an alternate energy path, realizing a transmission zero. The dominant mode of rectangular waveguide also excites the resonating mode in U-shaped ridge because of the asymmetries introduced by either offset or different length arms. A transmission zero below the passband is achieved by offsetting the U-shaped ridge relative to the waveguide center axis. A transmission zero above the passband is realized by using a centered U-shaped ridge with different length arms. Both adjustments can also be made simultaneously to achieve further flexibility in realizing the desired filter response. A fourth-order filter with two transmission zeros, one in the lower stopband while the other in the upper stopband is designed, fabricated and measured. Measurements show good agreement with the simulations thus demonstrating the practicability of the proposed structure.

Coefficient Reduction Method for Stopband Ripple Minimization of IFIR Filter

This paper presents a technique for minimization of ripples of interpolated finite impulse response (IFIR) filter. Single-stage and two-stage IFIR filters are designed using the Remez exchange algorithm. The performance of these filters is improved by minimizing the ripples in the stopband region by discarding zero-valued coefficients. The proposed technique yields the desired filter response of IFIR filters matching closely with the required response of finite impulse response (FIR) filter in the passband and stopband regions, providing very low computational complexity and sharp transition width as compared to the conventional FIR filter. In comparison to other existing techniques, the proposed algorithm reduces the stopband ripples significantly (the distortion in the frequency domain is reduced up to 61.20%). As a result, the power losses in the filtered signal are reduced, thereby enhancing the sensitivity and its consistency during the filtering process.

Design of a frequency spectrum-based versatile two-dimensional arbitrary shape filter bank: application to contact lens detection

A filter bank (FB) is an integral part of any image processing system. The designing of a FB generally involves modifying an existing FB or focusing on a particular property of the filter bank. Such FBs limit their use to a particular image. Through our work, we have devised a unique and novel approach for designing a two-dimensional arbitrary shape filter bank (2-D ASFB). This FB is inherently 2-D and eliminates the need for transforming a one-dimensional FB into 2-D. Its arbitrary nature expands its application to any image as compared to regular-shaped FBs currently in use. The novelty of the design lies in the fact that the designed FB can match the frequency spectrum of any image by reducing the error function between the frequency spectrum and the desired filter response of the FB. The error function has been minimized using the eigenfilter approach. After designing the low-pass analysis filter, perfect reconstruction constraint has been used to get a low-pass synthesis filter. In this paper, we have demonstrated the use of the 2-D ASFB specifically for contact lens detection (CLD). The proposed CLD system focuses on feature extraction using the 2-D ASFB. The support vector machine classifier is the same as in the existing systems. The results show improved correct classification rate as compared to the existing systems for IIITD and ND2013 contact lens database. This 2-D ASFB overcomes limitations posed by the existing filter banks with respect to separability, directionality, orthogonality, and shape. This FB can be effectively applied to any feature extraction application such as pattern recognition, biometrics, medical image processing.

A New Method for Designing of Stable Digital IIR Filter Using Hybrid Method

In this paper, a new technique for designing of a stable digital infinite impulse response filter, with improved performance in passband and stopband regions using quantum particle swarm optimization (QPSO) and artificial bee colony (ABC) algorithm, is explored in frequency domain. In the proposed method, QPSO technique is modified with exploiting the novelty of search and replacement mechanism of scout bee from ABC algorithm. For this purpose, a new design problem is constructed as a nonlinear minimization of mean square error between the designed and desired filter responses in passband, stopband, and transition band simultaneously, allowing permissible ripples in passband and stopband. Efficiency of the proposed technique is measured by several attributes like passband error, stopband error, total squared error (SE), maximum stopband attenuation, maximum passband error $$ \left( {e_{pb}^{\hbox{max} } } \right) $$ , passband ripple, and maximum phase deviation in passband. Experimental results evidence that a significant reduction is achieved in sum of the SE in passband and stopband from 12 to 54%, and the performance is not degraded due to quantization and truncation process. However, computation time in term of CPU time is increased from 0.77 to 4.1%, along with 2.62–7.43% hike in number of function evaluation, when compared to QPSO. A comparative study reveals that the proposed method yields better fidelity parameter as compared other evolutionary algorithms such as gravitational search algorithm, genetic algorithm, and variants of PSO. The proposed technique is also suitable for higher filter taps.

Generalized Synthesized Technique for the Design of Thickness Customizable High-Order Bandpass Frequency-Selective Surface

This paper presents a design guide for the implementation of thickness customizable high-order ( $N \ge 2$ ) bandpass frequency-selective surface (FSS). Admittance inverters are used to synthesize the filter response given desired characteristics such as filter type, center frequency, and bandwidth. The spatial inverter layers are essentially electromagnetic coupling interlayers that can be adjusted to customize the thickness of multilayered FSS without degrading the desired filter performance. A generalized equivalent circuit is used to provide physical insights of the proposed design. This synthesized technique can be adopted to deliver a versatile implementation capability of high-order FSS filters using various dielectric spacers with arbitrary thicknesses. Such a technique enables the realization of spatial filters with variable weight and size, while maintaining the desired filter response. To highlight its thickness controllability, a third-order bandpass FSS operating at the X-band (center frequency at $f_{0} = 10$ GHz) with $\approx 10$ % fractional bandwidth is synthesized in four different thickness configurations (electrical size varying from $\lambda _{0}$ /12 to $\lambda _{0}$ /6). The simulation results of all the four thickness customized configurations deliver the same filter response. To validate the proposed technique, two prototypes among the four design configurations are fabricated and measured in a free-space environment. Simulated and measured results show good agreement.

Designing an Inverter-based Operational Transconductance Amplifier-capacitor Filter with Low Power Consumption for Biomedical Applications

The operational transconductance amplifier-capacitor (OTA-C) filter is one of the best structures for implementing continuous-time filters. It is particularly important to design a universal OTA-C filter capable of generating the desired filter response via a single structure, thus reducing the filter circuit power consumption as well as noise and the occupied space on the electronic chip. In this study, an inverter-based universal OTA-C filter with very low power consumption and acceptable noise was designed with applications in bioelectric and biomedical equipment for recording biomedical signals. The very low power consumption of the proposed filter was achieved through introducing bias in subthreshold MOSFET transistors. The proposed filter is also capable of simultaneously receiving favorable low-, band-, and high-pass filter responses. The performance of the proposed filter was simulated and analyzed via HSPICE software (level 49) and 180 nm complementary metal-oxide-semiconductor technology. The rate of power consumption and noise obtained from simulations are 7.1 nW and 10.18 nA, respectively, so this filter has reduced noise as well as power consumption. The proposed universal OTA-C filter was designed based on the minimum number of transconductance blocks and an inverter circuit by three transconductance blocks (OTA).

오디오 이퀄라이저를 위한 주파수 응답의 고속 그래픽 표현 방법

This paper proposes a new method for fast graphic visualization of accurate frequency response of audio equalizer (EQ). When a logarithmic frequency scale is used, a frequency response in high resolution is required for accurate low-band frequency response. However, the high-resolution frequency response requires a huge amount of computational load, which makes the real-time graphic visualization of frequency response impossible. In order to solve the problem of computational load, the proposed method utilizes a low-resolution virtual frequency response in the mid band. It first computes the virtual frequency response of each filter of EQ in the mid band, and then moves it to the target band so that the result corresponds to the desired filter response. Then, it determines the final frequency response of EQ by combining all filter responses. The experiments confirm that the proposed method provides the frequency response of EQ which has an equivalent shape to that computed in high frequency resolution with huge computational load.

Opposition aided Cat Swarm OptimizationAlgorithm for Optimal Digital IIR High PassFilter Design

1 ABSTRACT: This paper presents a solution methodology for the designing of optimal and stable digital infinite impulse response (IIR) high pass (HP) filter by employing the cat swarm optimization (CSO) technique with oppositional learning. Because of the presence of the denominator terms, the error surface of digital IIR filters is non linear and multimodal. Therefore, the traditional designing techniques usually got trapped in the local minim. CSO is a population based global optimization technique which has global as well as local search capabilities. Here, the multicriterion optimization is used as the design criterion that undertakes the minimization of magnitude approximation error and minimization of ripple magnitudes while satisfying the stability constraints that are imposed during the design process. For the intent of starting with an improved solution set, the opposition based learning strategy is included in CSO. The developed algorithm is used to design the digital IIR high pass (HP) filter and attempts to find the optimal filter coefficients which are approximately close to the desired filter response. The computational results shows that the proposed algorithm is capable of designing the stable and optimal digital IIR HP filter structure that is better to the designs presented by other algorithms.

SIW‐based interdigital bandpass filter with harmonic suppression

ABSTRACTA novel configuration of interdigital bandpass filter based on the substrate integrated waveguide (SIW) technology is proposed. In addition to the interdigital resonators in SIW that determine the main response/characteristics of the filter, narrowing the width of the SIW at the center of the filter and additional vias at its input and output parts act as two additional control mechanisms to achieve the desired filter response. Moreover, dumbbells are etched to the ground side of the microstrip feeding sections at both ends of the filter to improve its harmonic suppression. A prototype filter is designed and fabricated for verification. The measured results are in good agreement with the simulations, and the filter exhibits very good harmonic suppression. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:66–69, 2015

A Generalized Analytical Approach for Designing of One Dimensional Photonic Crystal Based Optical Filter With Flat-Top Response

One dimensional photonic crystal based optical band pass filter has been analyzed using coupled mode approach in order to achieve a desired filter response in terms of full width at half maximum. The power transmittance through successive primitive cells of the crystal has been rationalized by considering weak coupling between the forward and specularly reflected waves within the crystal, which is modeled as distributed feedback structure. The time constants, associated with the optical resonator and responsible for a weakly coupled eigen mode to exist, have been estimated. These time constants would actually be used to determine the number of primitive cells, on either side of a defect, required to build up a desired mode. The collateral observations provide necessary conditions of resonance.

The design of waveguide filters based on cross‐coupled resonators

ABSTRACTThis article addresses the physical realization of crosscoupled waveguide filters based on electromagnetic (EM) simulations. For this design procedure, the filter structure is simulated by successively adding one resonator at a time. The desired filter response is achieved without the need of a global optimisation on all the mechanical dimensions within an EM simulator. This reduces the design time required for a crosscoupled waveguide filter and allows the possibility of building high‐order waveguide filters with complex crosscouplings. A sixth order X‐band dual‐band filter with a center frequency of 10 GHz and a fractional bandwidth of 1% is designed using this procedure and presented here as an example. Excellent agreement between simulation results and theoretical results from coupling matrix verifies the proposed approach. © 2014 Wiley Periodicals, Inc. Microwave Opt Technol Lett 56:3–8, 2014

Synthesis of high-order bandpass filters based on coupled-resonator optical waveguides (CROWs)

We present a filter design formalism for the synthesis of coupled-resonator optical waveguide (CROW) filters. This formalism leads to expressions and a methodology for deriving the coupling coefficients of CROWs for the desired filter responses and is based on coupled-mode theory as well as the recursive properties of the coupling matrix. The coupling coefficients are universal and can be applied to various types of resonators. We describe a method for the conversion of the coupling coefficients to the parameters based on ring resonators and grating defect resonators. The designs of Butterworth and Bessel CROW filters are demonstrated as examples.

Optimal matrix filter design with controlled mean-square sidelobe level

In this study, a simple approach for designing a matrix filter with controlled mean-square sidelobe level is proposed. Two methods are used for designing the matrix filter. In design method 1, the authors minimise the normalised mean-square error between the designed and the desired filter responses in the passband subject to the different normalised mean-square error constraints in the left and right stopbands. In design method 2, the objective function and the constraints in the design method 1 are reversed. By using Lagrange multiplier theory, the optimal solution and the optimal value of the optimisations are given, the equations of finding the optimal Lagrange multipliers are offered. In addition, the optimal matrix lowpass filters with symmetric stopband region and equally sidelobe level are given, the matrix codiagonalisation method is used for improving the design efficiency. Numerical results show that the proposed approach is effective for designing matrix filter and filtering short data records.

Analysis, design and applications of the triple-mode conductor-loaded cavity filter

This study presents the analysis and design of a new triple-mode filter that employs the recently proposed triple mode conductor-loaded cavity resonator. The resonator consists of a cubic-shaped metallic structure suspended in a metallic enclosure. The resonator is mounted in the cavity through a low-loss low-dielectric-constant support structure. The triple-mode conductor-loaded cavity resonator is considerably cheaper, easier to design and manufacture, and offers a significantly wider spurious-free response in comparison with the triple-mode dielectric resonator. A six-pole filter is designed using Ansoft HFSS employing the proposed triple mode conductor-loaded cavity resonator. The analysis shows that introducing asymmetry into the structure of the resonator in the form of chamfers or corner cuts creates the necessary perturbation to achieve the required coupling between the degenerate modes inside each block to realise the desired filter response. The six-pole triple-mode conductor-loaded cavity filter is fabricated and tested. Finally, two applications of the proposed concept are identified. The triple mode conductor-loaded cavity resonator is combined with higher Q-factor triple-mode ceramic resonators to realise a small size, high Q-factor filter with wide spurious-free response. Also, a direct-coupled band-stop filter is proposed employing the triple-mode conductor-loaded cavity filter.

Optimal Matrix Filter Design With Application to Filtering Short Data Records

This letter presents a simple computer-aided approach for designing matrix filter based on the least-square criterion. Three methods are considered for designing matrix filter. In design method 1, we minimize the normalized mean-square error between the designed and desired filter response in the passband subject to the normalized mean-square error constraint in the stopband. In design method 2, the objective function and the constraint in the design method 1 are reversed. In design method 3, the optimal matrix filter which has the general mean-square error is considered. Numerical results show that the proposed approach is effective for designing matrix filter and filtering short data records.

개별 공진기의 EM 시뮬레이션에 기초한 새로운 직접결합 대역여파기 설계 방법

이상적인 전송선을 가정하고 도출된 여파기 설계 공식에 의하여 대역여파기를 설계할 경우, 제작된 여파기는 중심 주파수의 이동 및 주파수 특성의 왜곡을 발생시키며, 주파수가 높아질수록 심각한 문제를 야기한다. 이를 해결하기 위하여 본 논문에서는 개별 공진기의 EM(Electro-Magnetic) 시뮬레이션을 기초로 한 새로운 여파기 설계 방법을 제안하였다. 이 방법은 여파기를 개별 공진기로 분리하고, EM 시뮬레이션을 통해 개별 공진기의 리액턴스(reactance) 기울기 및 인버터 상수와 같은 여파기 설계 파라미터를 추출한 후, 이것이 인버터와 리액턴스 기울기로 구성된 인버터-기준형 설계치와 같도록 조정하는 것이다. 이와 같이 조정된 공진기를 조합하여 구성된 여파기는 별도의 조정 없이 목적한 설계치를 만족하게 된다. EM 시뮬레이션 시 이미 선로의 분산(dispersion) 및 불연속(discontinuity) 효과를 고려하였기 때문에 더 이상의 조정이 필요 없으며, 이 방법은 인버터-기준형으로 환원되는 대부분의 여파기에 적용 가능하다. 본 논문에서는 5단 SIR 여파기를 예로 들어 여파기 설계의 전반적인 과정을 설명하였고, 평행결합선로 여파기(parallel coupled line filter) 및 hair-pin 여파기에 확장 적용한 예를 보여 이 방법의 타당성을 보였다. The BPF designed by the formula based on strip line shows the center frequency shift and distortion in filter response and this becomes more significant with higher frequency. In this paper, the novel design based on EM simulation is proposed. In the design, the filter is decomposed into individual resonators and, for each resonator, the reactance slope and the inverter values are measured and tuned to desired design values for a inverter BPF prototype. The filter composed with such resonators shows the desired filter response without further tuning. This is because possible effects of discontinuities and dispersion are included in the filter parameter extraction. The method can generally apply to all filters that can be transformed into inverter BPF prototype. The procedure is verified by designing a 5th-order SIR filter and quite general to adapt into the design of a parallel coupled line filter, and hair-pin filter.

Method for acoustic transducer calibration

A method of acoustic transducer calibration ( 200, 400 ) using a band limited pseudo random noise source with an internal digital signal processor ( 209, 403 ) to tailor audio characteristics of an internal microphone 103 and internal speaker ( 301 ) within a communications device ( 101 ) to insure consistent amplitude and frequency characteristics of these microphone and speaker transducer devices. The method offers and advantage such that tuning of the amplitude and frequency response consistently converges to the desired filter response with a filter type offering operational stability.

Fast algorithms for designing variable FIR notch filters

AbstractThe paper presents fast algorithms for designing finite impulse response (FIR) notch filters. The aim is to design a digital FIR notch filter so that the magnitude of the filter has a deep notch at a specified frequency, and as the notch frequency changes, the filter coefficients should be able to track the notch fast in real time. The filter design problem is first converted into a convex optimization problem in the autocorrelation domain. The frequency response of the autocorrelation of the filter impulse response is compared with the desired filter response and the integral square error is minimized with respect to the unknown autocorrelation coefficients. Spectral factorization is used to calculate the coefficients of the filter. In the optimization process, the computational advantage is obtained by exploiting the structure of the Hessian matrix which consists of a Toeplitz plus a Hankel matrix. Two methods have been used for solving the Toeplitz‐plus‐Hankel system of equations. In the first method, the computational time is reduced by using Block–Levinson's recursion for solving the Toeplitz‐plus‐Hankel system of matrices. In the second method, the conjugate gradient method with different preconditioners is used to solve the system. Comparative studies demonstrate the computational advantages of the latter. Both these algorithms have been used to obtain the autocorrelation coefficients of notch filters with different orders. The original filter coefficients are found by spectral factorization and each of these filters have been tested for filtering synthetic as well as real‐life signals. Copyright © 2007 John Wiley & Sons, Ltd.

Flat-passband 3 /spl times/ 3 interleaving filter designed with optical directional couplers in lattice structure

This paper presents a novel lattice optical delay-line circuit using 3 /spl times/ 3 directional couplers to implement three-port optical interleaving filters. It is shown that the proposed circuit can deliver three channels of 2/spl pi//3 phase-shifted interleaving transmission spectra if the coupling ratios of the last two directional couplers are selected appropriately. The other performance requirements of an optical interleaver can be achieved by designing the remaining part of the lattice circuit. A recursive synthesis design algorithm is developed to calculate the design parameters of the lattice circuit that will yield the desired filter response. As illustrative examples, interleavers with maximally flat-top passband transmission and with given transmission performance on passband ripples and passband bandwidth, respectively, are designed to verify the effectiveness of the proposed design scheme.

Robust least mean square adaptive FIR filter algorithm

The authors propose a new robust adaptive FIR filter algorithm for system identification applications based on a statistical approach named the M estimation. The proposed robust least mean square algorithm differs from the conventional one by the insertion of a suitably chosen nonlinear transformation of the prediction residuals. The effect of nonlinearity is to assign less weight to a small portion of large residuals so that the impulsive noise in the desired filter response will not greatly influence the final parameter estimates. The convergence of the parameter estimates is established theoretically using the ordinary differential equation approach. The feasibility of the approach is demonstrated with simulations.