1869 research outputs found
Sort by
A Novel Design Methodology for Integration of Optimized Wideband Elements with Aperiodic Array Topologies
No full textThe recent development of many new ultra‐wideband (UWB) array technologies has created a demand for antenna elements that can effectively operate over similar bandwidths. For example, the polyfractal [1] and RPS [2] topologies are capable of exhibiting remarkably wide frequency bandwidths on the order of 20:1, 40:1 or even more, depending on the array size. Often, the antenna elements that are capable of these extended bandwidths begin to develop several lobes in the radiation pattern and generate increased cross‐polarized radiation at their upper range of operating frequencies. A new type of ultra‐wideband antenna has been developed based on a spline‐shaping technique and a particle swarm algorithm (PSO) [3]. With proper attention to the radiation pattern, cross‐polarization, and return loss in the PSO cost function, this method is capable of producing UWB antenna elements that minimize all the aforementioned undesirable characteristics, making them very suitable for use in UWB array systems with bandwidths up to 4:1 and perhaps even wider
Synthesis of Arbitrary Sidelobes Sum and Difference Patterns with Common Excitation Weights
No full textThe synthesis of sum and difference patterns is a canonical problem widely dealt with by researchers working on antenna array synthesis. As a matter of fact, they are used as transmitting/receiving devices for search‐and‐track systems (e.g., monopulse radars [1]). In this framework, several procedures have been proposed to reduce the complexity of the beam forming network aimed at generating at least a couple of radiation patterns. Among them, the generation of an optimal sum pattern and a difference one has been carried out by means of a sub‐arraying strategy [2,3]. The simplification of the hardware complexity has also been addressed by sharing some excitations for the sum and difference channels [4]. Recently, the synthesis of low‐sidelobe sum and difference patterns with a common aperture has been carried out by perturbing the roots of the Bayliss distribution to match as much as possible a given Taylor distribution [5]. The discrete linear arrays have been successively obtained by sampling the resulting continuous apertures. In this work, the same array synthesis problem dealt with in [5] is addressed, and an innovative approach based on a deterministic optimization strategy is presented wherein the problem is formulated as the minimization of a linear function over a convex set. Taking advantage from the approaches proposed in [6] and [7] for the optimal synthesis of sum and difference patterns respectively, the proposed method allows one to synthesize patterns with arbitrary sidelobes (unlike [5])
Evolutionary Algorithms for Inverse Scattering: Advances and State-of-the-art Comparisons
No full textThis work is aimed at presenting the recent advances and the procedures available in the state‐of‐the‐art for the solution of inverse scattering problems through Evolutionary Algorithms (EAs). The main emphasis is on the use of population‐based optimization algorithms used for the retrieval of unknown objects embedded in an inaccessible region when illuminated by a set of microwave radiations. Starting from a description of the general architecture of EAs, advantages and limitation of state‐of‐the‐art approached are pointed out and discussed
A Qualitative Two-Step Inversion Approach for the Reconstruction of Subsurface Defects
No full textThe detection of subsurface objects such as landmine or archaeological find, the location of sedimentary layer for geological inspections, or the identification of cracks and voids in host structures are some examples of applications where the reconstruction of the position and the shape of unknown targets embedded in inaccessible regions is required. In this framework, the imaging methods based on electromagnetic inverse scattering theory can play a key role [1]. As a matter of fact, the electromagnetic and geometric properties of the region under test can be quantitatively reconstructed starting from the observation of the scattered field. Unfortunately, the problem at hand presents several drawbacks such as non‐linearity and ill‐posedness that need to be taken into account especially when dealing with complex scenarios. However, a considerable amount of a‐priori information is generally available in nondestructive testing and evaluation (NDT/NDE) applications, since the crack to be reconstructed is located in a known host medium [2]. Such a peculiarity can be profitably exploited in order to cope with the lack of information characterizing the inverse problem. In such a framework, microwave methodologies based on the use of heuristic optimizers and on the exploitation of the a‐priori information have been effectively used for the detection of a crack in a known host structure [3] or when dealing with more complex and realistic scenarios characterized by multiple defects [4]. The proposed approaches demonstrate their feasibility and effectiveness in providing a coarse estimation of the targets in a qualitative fashion, but they are not suitable for the retrieval of complex shapes. In this work, a two‐step procedure successfully adopted for NDT/NDE problems [5] has been employed for the qualitative reconstruction of complex subsurface targets. In particular, at the first step the target is localized and its shape is roughly estimated starting from the knowledge of the scattered field. Then, the second step is aimed at refining the contour of the target by means of a shape optimization technique characterized by the evolution of a level set function [6]
Compromise Pattern Synthesis by Means of Optimized Time-Modulated Array Solutions
No full textOriginally, the use of time‐modulated arrays was mainly devoted to the synthesis of low and ultra‐low sidelobes arrays for the detection of radar signals [1]. Successively, only a few works have considered the use of time‐modulated arrays for other applications (e.g., wireless communications [2]), although the first work proposing the use of time as an additional degree of freedom dates back to the 1950s [3]. Such an event has been probably caused by the main drawback of time‐modulation that is the unavoidable presence of undesired sideband radiations (SRs) in the radiated field due to the periodic commutation of the RF switches between the on and off states. A detailed analysis on such a topic has been recently presented in [4], where a close‐form relationship quantifying the power wasted in SR has been obtained
Simultaneous Optimization of Subarray Weights and Sizes for Low Sidelobe Synthesis of Large Array Antennas
No full textLarge array antennas of wide dimension are often used in several communication and radar systems. Thanks to their performance (e.g., the patterns are electronically steerable, the illumination can be controlled directly on the aperture, etc.), array antennas have replaced parabolic reflectors in many challenging and real applications. Nevertheless, large phased arrays still represent too expensive solutions because of the large number of radiating elements and the high circuit complexity. For this reason, the subarraying strategy has been widely adopted in order to simplify the antenna design and to achieve a better trafe‐off between cost and performances. Accordingly, the elements on the array aperture are grouped into clusters and a gain is assigned to each of them. Since the use of amplitude weights at the output of the subarrays generates unavoidable grating lobes [1], various strategies have been proposed to synthesize subarrayed antennas with low sidelobe levels (s) [2]‐[4]
Synthesis of Sub-Arrayed Monopulse Planar Arrays by Means of an Innovative Excitation Matching Method
No full textPlanar antenna arrays are widely used as transmitting and receiving part of monopulse trackers because of the need to gen‐erate sum and difference radiation modes to estimate the angular location of an unknown target. In such a framework, this paper presents an innovative synthesis technique able to synthesize two orthogonal sub‐arrayed difference patterns close to an optimal reference one. The proposed numerical results assess the effectiveness of the proposed approach also dealing with large arrays
An Innovative Spline-Based Shaping Approach for Ultra-Wideband Antenna Synthesis
No full textAntennas play a unique role in Ultra-wideband (UWB) systems because of their behaviour as a bandpass filter and the need of avoiding undesired distorsions in the spectra of the transmitted pulses. For this reason, traditional approaches for antenna characterization prove inadeguate, so innovative design procedures and measurement techniques are needed for antennas in UWB systems [1]. Up till now, the most common design approach (i.e., the Parametrical Approach) is based on the parametrization of some geometrical shapes and the optimization of their descriptors for fitting the requirements. The choice of the initial reference geometry is dictated by the a-priori knowledge on its range of application and achievable performance. In such a framework, examples of UWB antennas can be found in [2][3][4]. Another synthesis approach, called Non-Parametrical Approach, considers a description of the antenna structure in terms of a collection of elementary building blocks suitably-coded in an unknown array. In [5][6] some examples of antennas synthesized with such an approach and considering a binary encoding are presented. In this work, a novel UWB antenna design method is proposed in order to exploit the advantages of both the aformentioned approaches. In particular, some standard geometrical parameters (e.g., groundplane, feedline and substrate dimensions) are described according to a parametrical approach, while the design of the remaining features is obtained starting from a spline-based shape generator. This new design method exploits the simplicity of the classical parametric approach with the flexibility of the spline-based shape representation in order to obtain cheap and reliable antennas for UWB applications. In order to assess the effectiveness of the proposed approach, simulated and experimental results concerned with a representative UWB antenna design are presented and discussed. This is the author's version of the final version available at IEEE
Future Trends on Nanoantennas Synthesis
No full textThis paper aims at outlining some possible future challenges and solutions in nanoantennas design in the range of applications going from millimeter to nanometer scale. The growing interest for such systems, both in the field of miniature sensors and for applications in the visible and near infrared frequencies, requires effective design procedure in order to satisfy the desired specifications and the feasibility constraints. In such a context, the paper presents some non�]intuitive methodologies based on the swarm intelligence that could provide effective tools for nanoantennas synthesis. This is the author's version of the final version available at IEEE
Distributed Entity Search
No full textCapturing information about entities of the real world (i.e. locations, people, institutions and others) is a goal that is gaining more attention in today’s web of data. We believe that this capturing would only be possible if users can contribute and interact as they do in the real world. The contribution and interaction of users may take place over a distributed network where they can publish information about known entities. We think that the contribution of users will not happen, if the network can not be considered also as a source of information for them. Therefore, this PHD thesis aims to address the problem of finding entities (i.e. information about entities) that are related to the information needs of the user, in order to consolidate a web of data, which is based on entities. These entities need to be found from a collection, which can be distributed and where each entity can be described from the points of view of different users. In this proposal we analyze different layers of abstractions in the context of an entity-centric application, which allow users to define and share their entities. Then, we describe the problem of entity search in a distributed environment considering the different abstraction layers. We end with a discussion of possible approaches for the solution, where a network architecture for the search is proposed