Asymmetric Filter Research Articles

Unit Root Properties of Seasonal Adjustment and Related Filters: Special Cases

Abstract Bell (2012) catalogued unit root factors contained in linear filters used in seasonal adjustment (model-based or from the X-11 method) but noted that, for model-based seasonal adjustment, special cases could arise where filters could contain more unit root factors than was indicated by the general results. This article reviews some special cases that occur with canonical ARIMA model based adjustment in which, with some commonly used ARIMA models, the symmetric seasonal filters contain two extra nonseasonal differences (i.e., they include an extra (1 - B)(1 - F)). This increases by two the degree of polynomials in time that are annihilated by the seasonal filter and reproduced by the seasonal adjustment filter. Other results for canonical ARIMA adjustment that are reported in Bell (2012), including properties of the trend and irregular filters, and properties of the asymmetric and finite filters, are unaltered in these special cases. Special cases for seasonal adjustment with structural ARIMA component models are also briefly discussed.

Investigation on microwave photonic filter group delay performance

Investigation on the group delay performance of microwave photonic filters is presented. Analysis and simulation results show symmetrical distribution on the delayed optical signals in the impulse response is required to obtain a constant group delay performance. Experimental results for both symmetrical and asymmetrical tap distribution microwave photonic notch filters are presented showing the group delay response with <±25 ps and around 1 ns ripples, respectively.

Asymmetric apodization for the comma aberrated point spread function

This paper deals with the study of light flux distributions in the point spread function formed by an optical system with a one-dimensional aperture under the influence of the coma aberration. The traditional design of an asymmetric optical filter improves the resolution of a diffraction-limited optical imaging system. In this approach we explore the control of monochromatic aberrations through pupil engineering with asymmetric apodization. This technique employs the amplitude and phase apodization for the mitigation of the effects of third-order aberrations on the diffracted image. On introducing the coma wave aberration effect, the central peak intensity in the field of diffraction is a function of the edge strips width and the amplitude apodization parameter of a one-dimensional pupil filter, whereas the magnitude of the reduction of optical side-lobes is a function of the degree of phase apodization at the periphery of the aperture. The analytically computed results are illustrated graphically in terms of point spread function curves under various considerations of the coma aberrations and a different degree of amplitude and phase apodization. Hence, for the optimum values of apodization, the axial resolution has been analyzed using well-defined quality criteria.

An asymmetrical dual band bandpass filter

ABSTRACTA dual band bandpass filter consisting of a cascade of unit elements and shunt connected stepped open and stepped short circuited stubs, is described. The dual passbands can have unequal, asymmetrical width; the stop‐bandwidth between the desired bands and the harmonic upper bands is substantially increased. A prototype filter that finds application in communication systems is developed. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 59:163–168, 2017

A Low Cost Structurally Optimized Design for Diverse Filter Types.

A wide range of image processing applications deploys two dimensional (2D)-filters for performing diversified tasks such as image enhancement, edge detection, noise suppression, multi scale decomposition and compression etc. All of these tasks require multiple type of 2D-filters simultaneously to acquire the desired results. The resource hungry conventional approach is not a viable option for implementing these computationally intensive 2D-filters especially in a resource constraint environment. Thus it calls for optimized solutions. Mostly the optimization of these filters are based on exploiting structural properties. A common shortcoming of all previously reported optimized approaches is their restricted applicability only for a specific filter type. These narrow scoped solutions completely disregard the versatility attribute of advanced image processing applications and in turn offset their effectiveness while implementing a complete application. This paper presents an efficient framework which exploits the structural properties of 2D-filters for effectually reducing its computational cost along with an added advantage of versatility for supporting diverse filter types. A composite symmetric filter structure is introduced which exploits the identities of quadrant and circular T-symmetries in two distinct filter regions simultaneously. These T-symmetries effectually reduce the number of filter coefficients and consequently its multipliers count. The proposed framework at the same time empowers this composite filter structure with additional capabilities of realizing all of its Ψ-symmetry based subtypes and also its special asymmetric filters case. The two-fold optimized framework thus reduces filter computational cost up to 75% as compared to the conventional approach as well as its versatility attribute not only supports diverse filter types but also offers further cost reduction via resource sharing for sequential implementation of diversified image processing applications especially in a constraint environment.

Design of compact and miniaturize asymmetric SIR-DRA filter-antenna subsystem

The proposed work presents a compact filter–antenna subsystem design using asymmetric stepped impedance resonator filter and cylindrical dielectric resonator antenna. A cylindrical dielectric resonator antenna is excited from stepped impedance resonator through slot. The DRA is excited for HEM11 mode. Rather than utilizing customary 50 Ω interfaces, some intermediate impedance between filter and antenna is optimized to get the desired results. The assembly of both filter and antenna into one module leads to compactness in the RF front-end. The designed filter antenna subsystem has efficiency of 93%.

Synthesis and design of asymmetrical dual‐band bandpass filters with modified Richard's transformation

An exact synthesis method for asymmetrical dual-band bandpass filter (BPF) designs is presented with the proposed modified Richard's transformation (MRT). The MRT parameters are calculated first. Next, the filtering response is obtained according to the filter design specifications. Then, the component values of the LC circuit are obtained by an optimisation method. Finally, the LC circuit is transformed to its corresponding transmission line circuit. The discussions on the MRT are divided into two aspects. From the filtering response side, a set of parameters of the MRT is used so as to map a normalised symmetrical to an asymmetrical filtering response. By doing so, the bandwidths and the frequency ratio of the two passbands can be obtained with their desired values. From the circuit side, given that the classical Richard's transformation is a function of tan( θ ) while the proposed MRT is a function of tan( θ / n d ), dual-section commensurate transmission lines are used instead of the commonly used single-section ones. As synthesis and design examples, two second order and a cascading asymmetrical dual-band BPFs are demonstrated in a step-by-step procedure. Their experimental results are in a good agreement with the predicted ones thereby verifying the MRT-based synthesis procedure.

Modulation With Sinusoidal Third-Harmonic Injection for Active Split DC-Bus Four-Leg Inverters

Three-phase four-leg inverters are commonly employed to supply unbalanced loads avoiding the use of a transformer. A suitable output filter is necessary to improve the harmonic content of the output voltage and current waveforms. To this aim, different kind of filters, presenting both symmetrical and asymmetrical phase-to-phase and phase-to-neutral behavior, can be used. The paper discusses and analyzes the effects of different carrier-based modulation techniques, based on the independent control of the fourth leg from that of the other phases, with reference to the different filter topologies. The comparison, performed through extensive simulations and experimental tests, have demonstrated that in case of the asymmetrical filter utilization, such as the active split dc-bus (also known as split-link ), the conventional continuous and discontinuous space-vector modulations produce a significant harmonic content in the output voltages even at no-load condition. Moreover, the analysis is extended considering the interaction between the modulation strategy and load characteristics as linear, nonlinear, balanced and unbalanced loads. The problem is discussed in detail and a specific design procedure for the active split dc-bus is presented.

UWB Pulse Decomposition in Simple Printed Structures

The paper describes the ultra-wideband (UWB) pulse decomposition in simple printed structures aimed at low-cost and effective protection. The structure of an asymmetrical modal filter without resistors is considered, and the possibility of the attenuation by a factor of 55 is shown. Another structure—a turn of a meander line (ML)—is described, and the possibility of the attenuation by a factor of 2.5 is shown. Simulations without and with frequency-dependent losses in conductors and dielectrics are compared with experimental results. Based on the described principles, new devices can be designed which will be reliable, cheap, and radiation resistant due to the absence of any lumped components.

Robust Ground Target Detection by SAR and IR Sensor Fusion Using Adaboost-Based Feature Selection.

Long-range ground targets are difficult to detect in a noisy cluttered environment using either synthetic aperture radar (SAR) images or infrared (IR) images. SAR-based detectors can provide a high detection rate with a high false alarm rate to background scatter noise. IR-based approaches can detect hot targets but are affected strongly by the weather conditions. This paper proposes a novel target detection method by decision-level SAR and IR fusion using an Adaboost-based machine learning scheme to achieve a high detection rate and low false alarm rate. The proposed method consists of individual detection, registration, and fusion architecture. This paper presents a single framework of a SAR and IR target detection method using modified Boolean map visual theory (modBMVT) and feature-selection based fusion. Previous methods applied different algorithms to detect SAR and IR targets because of the different physical image characteristics. One method that is optimized for IR target detection produces unsuccessful results in SAR target detection. This study examined the image characteristics and proposed a unified SAR and IR target detection method by inserting a median local average filter (MLAF, pre-filter) and an asymmetric morphological closing filter (AMCF, post-filter) into the BMVT. The original BMVT was optimized to detect small infrared targets. The proposed modBMVT can remove the thermal and scatter noise by the MLAF and detect extended targets by attaching the AMCF after the BMVT. Heterogeneous SAR and IR images were registered automatically using the proposed RANdom SAmple Region Consensus (RANSARC)-based homography optimization after a brute-force correspondence search using the detected target centers and regions. The final targets were detected by feature-selection based sensor fusion using Adaboost. The proposed method showed good SAR and IR target detection performance through feature selection-based decision fusion on a synthetic database generated by OKTAL-SE.

Power-Normalized Cepstral Coefficients (PNCC) for Robust Speech Recognition

This paper presents a new feature extraction algorithm called power normalized Cepstral coefficients (PNCC) that is motivated by auditory processing. Major new features of PNCC include the use of a power-law nonlinearity that replaces the traditional log nonlinearity used in MFCC coefficients, a noise-suppression algorithm based on asymmetric filtering that suppresses background excitation, and a module that accomplishes temporal masking. We also propose the use of medium-time power analysis in which environmental parameters are estimated over a longer duration than is commonly used for speech, as well as frequency smoothing. Experimental results demonstrate that PNCC provides substantial improvements in recognition accuracy compared to MFCC and PLP for speech in the presence of various types of additive noise and in reverberant environments, with only slightly greater computational cost than conventional MFCC processing, and without degrading the recognition accuracy that is observed while training and testing using clean speech. PNCC also provides better recognition accuracy in noisy environments than techniques such as vector Taylor series (VTS) and the ETSI advanced front end (AFE) while requiring much less computation. We describe an implementation of PNCC using online processing that does not require future knowledge of the input.

URBAN VEGETATION MAPPING BASED ON THE HJ-1 NDVI RECONSTRCTION

Abstract. HJ-1A/B NDVI (HJ NDVI) time-series data possess relatively high spatio-temporal resolution which is significant for the research on urban areas. However, its application is hindered by noise resulting from the restrictions of imaging quality and limits of the satellite platform. The NDVI noise reduction is necessary. Some noise-reduction techniques including the asymmetric Gaussian filter (AG), the double logistic filter (DL), the Savitzky-Golay (S-G) filter and the harmonic analysis (Hants) of NDVI time-series have been used to carry out the NDVI time series reconstruction, and based on the comparison results of different filter, S-G filter is the optimal in the application on urban areas. Finally,urban vegetation mapping is carried out based on the new HJ NDVI.

URBAN VEGETATION MAPPING BASED ON THE HJ-1 NDVI RECONSTRCTION

HJ-1A/B NDVI (HJ NDVI) time-series data possess relatively high spatio-temporal resolution which is significant for the research on urban areas. However, its application is hindered by noise resulting from the restrictions of imaging quality and limits of the satellite platform. The NDVI noise reduction is necessary. Some noise-reduction techniques including the asymmetric Gaussian filter (AG), the double logistic filter (DL), the Savitzky-Golay (S-G) filter and the harmonic analysis (Hants) of NDVI time-series have been used to carry out the NDVI time series reconstruction, and based on the comparison results of different filter, S-G filter is the optimal in the application on urban areas. Finally,urban vegetation mapping is carried out based on the new HJ NDVI.

Designing asymmetric multilayered membrane filters with improved performance

Abstract Asymmetric multilayered filters, comprising a series of membranes with varying pore sizes stacked on top of one another, allow filtration to be tailored in a variety of novel ways. We develop a network model that systematically captures the complex filtration behaviour in such multilayer filters. The model allows us to understand the response of the system when challenged with a particular feed composition, characterized through the particle size and adhesivity to the membrane. We show how the model enables comprehensive and time-efficient sweeps in parameter space to be conducted that determine the optimal multilayered filter configuration for a given filtration challenge, classified by the number of membrane layers, the change in pore size between each layer (filter taper angle), and the level of trans-pore interconnectivity between each layer. The model allows us to isolate and analyse the effect of each of the specific filter characteristics and identify the practical merits and disadvantages. In particular, we predict that the optimal arrangement for maximizing throughput through the filter is to have pore radius gradually decreasing with depth, and a slight level of pore interconnectivity, with the precise set-up a function of the particle size, adhesivity and number of filter layers. The results of the analysis are used to draw conclusions on the design of membrane filters for optimal filter performance.

A Design Approach to Linear‐Phase FIR Filters with Odd‐Symmetric Transition Bands Using Piecewise Exponential Functions

SUMMARYThis paper proposes a novel method for designing linear‐phase finite‐impulse response digital filters with an asymmetric transition band. The proposed filters use a form of piecewise exponential functions in the frequency domain where transition characteristics are determined by giving only two fixed feature points. The design method was evaluated in two ways. First, we evaluated a designed asymmetric transition band filter, and the results revealed that evaluated errors in the proposed filters were equivalent to well‐known existing filters. Then, it was shown that a three‐channel filter bank with an asymmetric transition band and linear‐phase property could be implemented.

ASYMMETRIC FIBER TAPER FOR NARROW LINEWIDTH COMB FILTER

The employment of asymmetric optical fiber taper as a means for producing narrow linewidth comb filter is proposed and demonstrated. Fiber taper with different values set for the up-taper and down-taper transition regions was used to produce narrow linewidth comb filter through coupling interaction of light in the asymmetric fiber. Two configurations; single-pass and bidirectional fiber taper filters were studied and analyzed in this project. Results showed narrower 3-dB linewidth for asymmetric taper compared with uniform taper for single pass configuration. The asymmetric taper linewidth was improved further in bidirectional configuration, narrowing down to 2 nm. Bidirectional asymmetric taper filter recorded extinction ratio of 27.14 dB, which was 18 dB and 3 dB better than single-pass asymmetric taper and bidirectional uniform taper respectively. The findings emphasize the attractiveness of bidirectional asymmetric taper as a high performance optical filter.

Computational Cost Reduction for &lt;italic&gt;N+2&lt;/italic&gt; Order Coupling Matrix Synthesis Based on Desnanot-Jacobi Identity

Matrix inversion is routinely performed in computational engineering, with coupling matrix filter synthesis considered here as just one of many example applications. When calculating the elements of the inverse of a matrix, the determinants of the submatrices are evaluated. The recent mathematical proof of the Desnanot-Jacobi (also known as the “Lewis Carol”) identity shows how the determinant of an N+2 order square matrix can be directly computed from the determinants of the N+1 order principal submatrices and N order core submatrix. For the first time, this identity is applied directly to an electrical engineering problem, simplifying N+2 order coupled matrix filter synthesis (general case, which includes lossy and asymmetrical filters). With the general two-port network theory, we prove the simplification using the Desnanot-Jacobi identity and show that the N+2 coupling matrix can be directly extracted from the zeros of the admittance parameters (given by N+1 order determinants) and poles of the impedance parameters (given by the N order core matrix determinant). The results show that it is possible to decrease the computational complexity (by eliminating redundancy), reduce the associated cost function (by using less iterations), and under certain circumstances obtain different equivalent solutions. Nevertheless, the method also proves its practical usefulness under constrained optimizations when the user desires specific coupling matrix topologies and constrained coefficient values (e.g, purely real/imaginary/positive/negative). This can lead to a direct coupling matrix constrained configuration where other similar methods fail (using the same optimization algorithms).

A Reconfigurable Microwave Combline Filter

A general cascaded filter design technique is implemented to get a tunable narrow-band filter response based on the general Chebyshev bandpass filter. A cavity combline microwave filter is fabricated by cascading two asymmetrical filters without using an isolator between them. Tuning is provided by means of the screws on top of each resonator of the cavity combline filter. An optimization is applied to get the desired response. The designed example is presented together with the simulation and measurement results. The measured data are in good agreement with the simulation results.

Ultra-Miniature SIW Cavity Resonators and Filters

This paper presents ultra-miniature substrate integrated waveguide (SIW) cavity resonators, and filters by employing ramp-shaped slots as interdigital capacitors (IDCs) to force the structure to operate in the first negative-order resonance mode. Additionally, a metal patch in the middle metal layer along with disconnected vias is used to increase the equivalent series capacitance of the resonator and accordingly the miniaturization factor. By applying this method to half-mode SIW (HMSIW) and quarter-mode SIW (QMSIW) resonators, 90%, and 95% of miniaturization is achieved, respectively, compared to conventional full-mode SIW resonators. Afterwards, a two-pole bandpass filter is proposed based on the presented QMSIW resonator. Also, by using a combination of HMSIW and QMSIW ultra-miniature resonators, two trisection filters with a controllable transmission zero on either side of the passband are presented. To the best of authors' knowledge, this is the first disclosure of simultaneous use of HMSIW and QMSIW resonators to achieve asymmetric filter response with an ultra-compact size.

Effect of waist diameter and twist on tapered asymmetrical dual-core fiber MZI filter.

A compact in-fiber Mach-Zehnder interferometer (MZI) filter fabricated from custom-designed asymmetrical dual-core fiber is numerically analyzed in detail and experimentally verified. The asymmetrical dual-core fiber has core diameters and a core pitch of 6.9, 6, and 19.9 μm, respectively. The fiber tapering technique is introduced to fuse the originally uncoupled cores into strong coupling tapered regions. The length and diameter of the waist region have a close impact on the splitting ratio, which further affects the spectral properties of the MZI filter. The field evolution with varied waist parameters is characterized by the finite element method and beam propagation method. Repeatable comb filters with ∼15 dB extinction ratio are successfully achieved under the guidance of simulated optimum conditions. The twist-induced circular birefringence gives rise to a retardance that causes the spectral shifts of the MZI filter. The theoretical and experimental results confirm that the relative wavelength shift is proportional to the retardance, which follows a sinc function in the limit of a large twist rate.