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Slice regular functions on real alternative algebras
No full textIn this paper we develop a theory of slice regular functions on a real alternative algebra . Our approach is based on a well-known Fueter's construction. Two recent function theories can be included in our general theory: the one of slice regular functions of a quaternionic or octonionic variable and the theory of slice monogenic functions of a Clifford variable. Our approach permits to extend the range of these function theories and to obtain new results. In particular, we get a strong form of the fundamental theorem of algebra for an ample class of polynomials with coefficients in and we prove a Cauchy integral formula for slice functions of class
A Miniaturized UWB Antenna for Wireless Dongle Devices
No full textIn this letter, a planar Ultra WideBand (UWB)antenna suitable for the integration in wireless Universal Serial Bus (USB) dongles is described. The antenna has a bandwidth equal to 2GHz from 3GHz up to 5GHz with return loss values below −10 dB in the whole frequency range. To comply with UWB system needs, the antenna presents good distortionless properties when employed in a TX/RX system. Moreover, thanks to its simple shape and miniaturized geometry, the proposed prototype can be easily integrated and printed on dongle PCBs. In order to assess the reliability and efficiency of the antenna, a selected set of results from the experimental validation are shown and compared with the outcomes of the numerical simulations carried out during the synthesis process. (c) 2008 IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other users, including reprinting/ republishing this material for advertising or promotional purposes, creating new collective works for resale or redistribution to servers or lists, or reuse of any copyrighted components of this work in other works
Array Thinning Through Binary Sequences
No full textThinning is a standard technique to reduce the power consumption, hardware complexity, cost, and weight of large arrays [1][2]. However, array thinning does not allow a suitable control of the peak sidelobe level (PSL), as for filled arrays, with a reduction of the array performances [1][2]. In the literature, several techniques have been proposed for the design of thinned arrays with low sidelobes [1]�][4]. In a chronological order, arrays were at first thinned by deterministic techniques, but no significant advantages on the PSL reduction have been obtained over random approaches [1]. Successively, stochastic optimization techniques have been widely and successfully applied [3][4]. However, such techniques present high computational costs when applied to large arrays, and they do not allow a�]priori estimates of the expected performances for a given aperture size and thinning factor [2]. More recently, thinned arrays have been synthesized by exploiting the autocorrelation properties of binary sequences derived from Difference Sets (DSs) [2][5]. Such an approach has several advantages over traditional thinning techniques. It is computationally efficient and its performances are predictable [2]. However, DSs exist only for a limited subset of configurations, and their features cannot be exploited in a general way [2][5]. In order to apply the same strategy to a wider set of array configurations, sequences which are sub�]optimal with respect to DSs can be considered. For instance, Almost Difference Sets (ADSs) [6] are good candidates for large array thinning, since they represent a generalization of DSs with several similar properties [6]. This paper is aimed at analyzing the applicability of ADSs to the design of thinned linear arrays, as well as the effectiveness of such an array synthesis technique in terms of beam�]pattern features. Selected numerical results are provided to assess the performances of the proposed approach also in comparison with state�]of�]the�]art thinning techniques with predictable PSL behaviour
A Time-Based Approach for the Synthesis of Antennas for UWB Communication Systems
No full textIn Ultra‐Wideband (UWB) Communications, the design of the radiating system is a very demanding task. Since high data rates are obtained by transmitting very short temporal pulses, the correct reception of the transmitted waveforms plays a fundamental role to guarantee the reliability of the whole UWB system. Under these hypotheses the design of the antennas as independent devices is no more acceptable. Consequently, customized synthesis techniques are needed [1] as well as appropriate analysis tools for an accurate description of the behavior of the antennas in the time domain [2]. In this paper, an innovative approach for the design of antennas compliant to the UWB requirements is presented. In such an approach, the whole system constituted by both transmitting/receiving antennas and the communication channel is modeled in order to allow an accurate characterization of the whole set of interactions and mutual effects. Besides a good impedance matching over the operating bandwidth, UWB antennas are characterized by distortionless propagation properties suitable to assure a correct reception of the UWB waveforms. Towards this end, a Particle Swarm Optimizer (PSO) [3] is suitably integrated into a time‐domain (FDTD) electromagnetic simulator
Multi-Frequency/Multi-Scaling Techniques for the Electromagnetic Inversion of Lossless Profiles: A Numerical Comparison
No full textStarting from the iterative multi�]scaling approach developed for monochromatic illuminations, two multi�]resolution strategies have been studied for dealing with multi�]frequency inverse scattering experiments. The first approach is based on a multi�]scaling frequency�]hopping reconstruction scheme, while the second one is concerned with a simultaneous multi�]resolution processing of multi�]frequency data. In this contribution, a comparative assessment is performed by means of a set of representative experiments in order to evaluate the reconstruction accuracies of the proposed implementations also in comparison with the monochromatic multi�]step process
Innovative Approaches Based on a Reactive Sorting Algorithm for Sum and Difference Antenna Pattern Design
No full textThis work presents two new approaches for the design of sum and difference antenna array. The first approach considers a configuration of sub-arrays that minimizes a “residual error” functional, while the second one a configuration that minimizes a “gain sorting” functional. The obtained results show that by means of such methods difference pattern close to the optimal ones can be obtained with simpler feed networks. This is the author's version of the final version available at IEEE
A Non-Destructive Microwave Approach for the Detection of Multiple Defects in Industrial Products
No full textThe non�]destructive inspection is a key�]problem in many industrial processes since the detection of defects or cracks in the products is mandatory. Many tomographic approaches that have been proposed are based on the use of interrogating microwaves and their effectiveness in inspecting dielectric or conductive materials has been demonstrated. In general, a NDT/NDE problem solved through an inverse scattering technique is still ill�]conditioned and non�]linear. However, unlike standard microwave imaging problems where a complete image of the unknown investigation domain is required, a lot of a�]priori information on the scenario under test (the industrial product) is available. In this framework, Caorsi et al. proposed an optimization technique (FGA) [1], where a reduction of the number of problem unknowns was achieved by exploiting such an a�]priori information about the inspected geometry. As a matter of fact, a non�]destructive inspection is aimed at detecting an unknown defect inside a known unperturbed host medium lying on a known background. Starting from this assumption, the a�]priori information on the unperturbed structure was exploited by means of a suitable Genetic Algorithm (GA). As a consequence, the inverse scattering problem in hand was significantly simplified since the unknowns was reduced to an array of geometric parameters of the defect: the position of the defect, its size and orientation, and its electromagnetic properties
Recent Advances on the Use of Kernel-Based Learning-By-Examples Techniques for Electromagnetic Subsurface Sensing
No full textElectromagnetic approaches based on learning‐rom‐samples(LFS) techniques [1] have been proposed for the on‐line [after the learning process (or training phase) performed once and off‐line] detection of subsurface objects
Particle Swarm Optimization for Real-Time Adaptive Array Control
No full textThis paper describes the application of the particle swarm optimizer to the real time adaptive antenna control
Extending a geo-catalogue with matching capabilities
No full textTo achieve semantic interoperability, geo-spatial applications need to be equipped with tools able to understand user terminology that is typically different from the one enforced by standards. In this paper we summarize our experience in providing a semantic extension to the geo-catalogue of the Autonomous Province of Trento (PAT) in Italy. The semantic extension is based on the adoption of the S-Match semantic matching tool and on the use of a specifically designed faceted ontology codifying domain specific knowledge. We also briefly report our experience in the integration of the ontology with the geo-spatial ontology GeoWordNet