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A Darknet is an overlay network within the Internet, and packets’ traffic originating from it is usually termed as suspicious. In this paper common machine learning classification algorithms are employed to identify Darknet traffic. A ROC analysis along with a feature importance analysis for the best classifier was performed, to provide a better visualisation of the results. The experiments were conducted in the new dataset CIC-Darknet2020 and the classifiers were trained to both binary and multiclass classification. In the first classification task, there were two classes: "Benign" and "Darknet", whereas in the second there were four classes: "Tor", "Non Tor", "VPN" and "Non VPN". An average prediction accuracy of over 98% was achieved with the implementation of Random Forest algorithm for both classification tasks. This is the first work, to the best of our knowledge providing a comprehensive performance evaluation of machine learning classifiers employed for Darknet traffic classification in the new dataset CIC-Darknet2020.

An alternative variational modal analysis technique is contributed by this study. Although the weak form of the Maxwell equations is employed, instead of using the finite elements technique, the authors utilise entire/global domain vectorial basis functions. In such a case, to assist performance, the basis functions must comply with the boundary conditions. Since in general, this is a difficult task, they adopt the following strategy. They transform the initial convex cavity using coordinate transformation to a canonical one, where a known complete set of vectorial basis functions exist. Then, taking advantage of the form invariance property of the Maxwell equations, in the transformed domain, the authors solve the canonical variational problem and acquire the respective solution to the initial problem by the inverse electromagnetics transformation. Summarising, the contributing concept is to employ a coordinate transformation to a canonical shape employing ‘transformation electromagnetics’ approach as a pre-processing tool to enlarge the scope of a classical electomagnetics (EM) variational eigen-analysis using the canonical shape's vector modes.

Novel dual-element antenna arrays suitable for small devices of multiple-input-multiple-output (MIMO) applications have been designed and fabricated. The antenna elements have semi-printed structure, are fractally shaped, and operate in ISM (2.4-2.489 GHz) band as well as between 5 and 6 GHz. Although the size of the designed antenna prototypes is small and the elements are positioned too close to each other, correlation coefficients lower than 0.1 and satisfactory levels of mean effective gain have been obtained.

The use of conformal antennas in a MIMO link scenario is investigated. Conformal slot antennas are considered both in the transmitter and the receiver. First, a new modified correlation coefficient is derived that goes beyond the Clarke coefficient and takes into account the element radiation pattern. Secondly, a hybrid formulation that accounts for the impact of the mutual coupling and the pattern dependent correlation on the capacity is presented. The mutual coupling for slots placed circumferentially on a paraboloid substrate is derived using a rigorous approach based on Uniform Theory of Diffraction (UTD). The capacity is evaluated for the case of Rayleigh fading channel considering the new pattern dependent correlation coefficient and the conformal antenna mutual coupling. The planar case is included as a limiting case. It is shown that for conformal antennas on a paraboloid the capacity degradation compared to the planar case is up to 0.5 bps/Hz due to coupling and correlation.

The current work contributes a detailed design of overlapping element direct radiating arrays for satellite communications employing the elements on a planar host. Direct radiating arrays are undisputedly considered as the next step in the space sector of communication industry but their advent is not without challenge. Direct radiating arrays can provide the highly adaptive performance needed for extremely demanding terrestrial and satellite communication cases but unfortunately their cost is also high. This cost is mainly due to the number of control points, (phase shifters plus amplifiers), needed to meet the specifications. Thus the quest for this number reduction is ongoing. Currently, there is a paradigm shift towards using not non-overlapping but overlapping radiating elements. The current work addresses the problem and assesses the solution's potential.

In the current work we focus on sparse array design employing overlapping radiating elements. In this case, the underlying sparse grid shapes the broadside directivity far-field pattern while the overlapping flat-top producing sub-arrays eliminate the scanning loses. In detail, when overlapping arrays are involved the design process is as follows: Perform broadside design, (not scanning beam), using elements' size that keeps Grating Lobes just out of the Field of View (FoV). Since we use Flat-top elements their directivity is reduced and thus their number and/or their size should be increased to balance the two directivity trends. If the element number increase in the previous step is lower than the respective element number increase due to scanning losses when employing non-overlapping arrays, (and non-Flat-topped element), then we have an accepted solution; In most of the cases, this means that using overlapping we achieve a remarkable reduction in the number of control points.

A study of the maximally sparse large planar arrays with electrically large elements is presented. The conditional probabilities of the element placements and their resulting auxiliary radiation integrals are derived. Through them the average and the directivity pattern formulas are also derived. Employing these formulas, we present a convex method that provides a solution to the maximally sparse problem when main lobe constraints are imposed on the directivity pattern. In particular, by taking the possible types of elements into account, we manage to obtain the lower bound of the directivity that an array should exhibit. This lower bound is analytically derived in the form of a Pareto (sub-) set that classifies the possible arrays into feasible and nonfeasible ones. This Pareto set can also enable tradeoff studies to be conducted without the need to consider the full range of every parameter. From the procedure, several acceptable combinations of elements are obtained. Simulation results, which confirm the methodology, are presented.

A deterministic method for the design of direct radiating arrays for multibeam satellite applications is presented in the current work. The method embodies the following steps: First, we consider the problem of continuous aperture synthesis, subject to directivity-pattern mask constraints. We succeed in stating the problem as a convex magnitude antenna design that exhibits a second-order cone program form. The solution provides the optimum continuous aperture current-density distribution. Second, exploiting the optimum solution, analytical formulas, in the form of the Pareto front, are presented through which the proposed method determines the minimum number of radiating elements that must be used in the process of transforming the continuous aperture to an antenna array. Third, an effective deterministic sampling approach is contributed to produce a discrete array with the desired characteristics. Armed with the above, the current work provides a generalized framework for the design of direct radiating arrays for multibeam satellite applications. The method is validated by the provided design examples.

In this work, the design, fabrication, and testing of low sidelobe level (SLL) Butler matrix-based beamformers is presented. The paper is divided in two parts. The first part deals with the conventional technique of simultaneous excitation of input ports. The second part introduces some novel modified low SLL Butler matrices, as an alternative advantageous design choice. Circuit architecture makes use of asymmetric branch line couplers able to provide high values of output power division ratios. Radiation patterns with SLLs far lower than −23 dB are achieved, without the use of any additional circuitry, in opposition to the case of simultaneous port excitation. Apart from SLL reduction, the switched line-phase shifter technique is applied in order to increase the number of radiated beams and improve scanning coverage. The beamformers are suitable for interference suppressing point-to-multipoint ground communications, satellite and radar/EW/SIGINT systems. Several microstrip circuit prototypes are designed, fabricated, and tested, whereas extended simulation and measurements results are adduced.

The problem of optimized multibeam array synthesis is common in Modern Satellite Communications. In this work a new software tool for ADvanced Aperiodic Multibeam Array Synthesis (ADAMAS) is presented. It is based on the combination of Convex Aperture Synthesis with Pareto Front theory resulting both in the minimization of the computation time and the reduction of the number of required elements and the size of the host area. The software can handle demanding cases such as global coverage from a GEO satellite.

High-frequency methods employed for the perfect electrically conducting circular cylinder form two sets. The uniform theory of diffraction (UTD)-based ones are valid outside the paraxial region while there are others that are accurate, close to the axis of the cylinder. Here we present a uniform asymptotic solution for the surface magnetic field valid both within and outside the paraxial region of a perfect electrically conducting circular cylinder. This is achieved by approximating the Hankel functions by a uniform asymptotic expansion within the spectral integral representation of the relevant Green's function. All the resulted integrals are evaluated analytically in an exact fashion. Such a solution is of interest both for theoretical and for practical reasons. From a theoretical point of view, it is important to have a closed-form solution that copes with the canonical problem of a perfect electrically conducting circular cylinder. From a practical point of view, such a solution provides mutual coupling results and thus predicts compatibility and interference between conformal slot antennas mounted on constant radius cylindrically shaped perfectly conducting hosts. Validity of the proposed asymptotic solution is provided by comparison with published results.

In this article, the design of a cylindrical beamforming array (CBA) is presented. The array is conformed over a ring of a conducting circular cylinder. From the total number of elements, M, of the array, a subset of N successive elements is enabled each time. The selection of the subset is based on the minimization of the angle between its broadside direction and the direction of arrival (DOA) of the signal of interest (SOI). Furthermore, by adaptively combining the outputs of the active subarray, the gain of the system is maximized. The cylindrical beamforming array is integrated into the CDMA acquisition phase, where a joint process of code acquisition and smart-antenna adaptation is applied. The array is implemented for the uplink of a base-station receiver of a wireless communications system. A detailed justification and a performance evaluation under various simulation scenarios, which include integration into spatial and two-dimensional rake receivers, are also presented.

An optimization procedure for the layout assessment of electrically large but finite planar arrays is presented. The synthesis takes into account the desired directivity pattern that is prescribed employing bound constraints. Moreover, the size of the radiators is taken into account, which results in a hard nonoverlapping, between the elements, constraint. The latter should not be violated if we want the attained solution not only to obey the far-field mask, but also to be physically realizable. As stated, the optimization problem is twofold. An antenna design is associated with a packing problem. In order to take the constraints on the layout into account and solve the whole problem, we propose the constraint relaxation approach, which is equipped with a packing algorithm. Our study is applied to various initial geometries, and the resulting arrays appear to comply with the desired pattern and the nonoverlapping constraint. Several examples for different cases including symmetric arrays and a study on maximally sparse arrays are presented, which show the applicability and merit of the method.

A design procedure for the synthesis of planar arrays is presented. Synthesis takes into account the desired pattern and the constraint on the directivity index. It makes use of the perturbation method in conjunction with the Lagrange multiplier theory. Starting from an initial array we perturb the element positions by employing an iterative technique. In the iteration, by setting the first variation of the Lagrangian (Cost function) equal to zero we derive the perturbed positions. Perturbation is applied simultaneously along two independent variables, (element coordinates x and y). The final position of the elements results from the last iteration where the stopping criteria are met. The choice of the initial array takes into account the number of elements and the reduction need of nonuniformity in the excitation. Our study is used for various initial geometries and the resulting arrays are shown to comply with the desired pattern and the directivity index.

A design procedure for the synthesis of a coupled active antenna oscillator array is presented. Such an array is synthesized by deriving two sets of parameters: the radiators' positions and the oscillators' outputs. The outputs are used to excite the radiators. Minimization of the mean square error between the desired pattern and the resulting one is made. Synthesis starts from an initial array, which is perturbed iteratively by varying simultaneously the element excitations and positions. In the iteration, the first variation of the cost function is set equal to zero. The final array results from the last iteration, where the stopping criteria are met. The procedure designs simultaneously both the antenna and the attached coupled oscillator array providing viable solutions. The second by properly configuring the tuning parameters through the use of closed-form formulas. The resulting arrays are shown to comply with the desired pattern and the nonlinear dynamics thus proving the validity of our method.

A geometry synthesis procedure for arrays by the help of the orthogonal method (OM) is given in the work at hand. We start from an initial array with a given excitation and we perturb the element positions by combining an iterative technique with the OM. The final position of the elements is found from the last iteration where the desired approximation of the pattern is obtained. It is noticed that our formulation does not give always a successful outcome, since the search can be trapped in a local minimum. Thus, the successful issue comes from a suitable selection of the initial array. Cases with uniformly excited arrays or arrays with less number of excitations than the number of the elements are studied. Several examples for different cases will be presented and will show the applicability of the method.

An analysis method for multiconductor transmission lines embedded in inhomogeneous bi-anisotropic media is presented. The Maxwell-Boffi equations, accompanied by the Maxwell-Minkowski ones, are expressed as Taylor series of the operating frequency where the zeroth- and first-order terms are retained. The reduced problem is solved using the potential formulation through the static 2-D free-space Green's function. The method of moments is employed to numerically solve the set of quasi-TEM integral equations, to produce the Telegrapher's equations, and to derive the circuit parameters in matrix form. The procedure is augmented by providing in closed form the field-coupling integrals.

A4 4 Butler matrix (BM) optimized for UMTS appli- cations is presented. Special care is taken for the design of the elliptic couplers and the line crossovers. The BM is fabricated by conventional photolithography on a single laminate. No expensive double layer/multi- layer or high permittivity substrates or high-temperature superconduc- tors are used. The design is compact and complies with the bandwidth specifications of the UMTS band. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 585-588, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop. 22200

The current work is the theoretical framework of the Research Project “Thales” entitled: “Development of electromagnetic simulation and design tools for digitally controlled and multifunctioning RF-microwave stages and subunits which retain characteristics-specification supporting Software Defined (SDR) and cognitive Radios (CR)”. Thus, a review of the analytical and numerical eigenenalysis tools developed and used under the framework of this project is presented herein. An abstract description of these methods in addition with some indicative results is thus presented.

In the past 10 years due to their attractive features, the characteristic modes have been applied widely for the wideband and Multiple Input Multiple Output (MIMO) antennas design. In these works the radiator was a metallic structure located in air. Fabres in [M. C. Fabres, “Systematic Design of antennas using the theory of characteristic modes.” Universidad Politecnica de Valencia, Valencia, Ph.D. dissertation, pp 118–120, February 2007] applied the classical theory of characteristic modes to study parallel plates separated by air. However, utilizing the typical characteristic modes analysis the resulting electric eigencurrents do not give clear information about the structure radiation.

A Butler matrix (BM) for UMTS applications is presented. The Butler matrix was fabricated by conventional photolithography on a single laminate. The design is compact and complies with the required bandwidth. The design is based on the use of an elliptical coupler with certain geometrical characteristics, and a Lange coupler as a crossover. Furthermore, a design-scaling procedure that produces an N times N Butler matrix by using two (N/2)times(N/2) Butler matrices is given. The presented performance extrapolations clarify the potential and scalability of our approach

An efficient numerical algorithm for the analysis of printed antennas on a dielectric coated circular cylinder is presented. The formulation employs the spectral domain approach. Green's function is evaluated via Olver's uniform asymptotic expansions. The Fourier summation is transformed into integration and the asymptotic part of the integral is evaluated in closed form. The whole procedure results in a numerical algorithm that is at least as accurate and efficient as the respective one for the planar structure. The present approach can be applied for any source-receiver position and any cylinder radius

The orthogonal method, a powerful and versatile array design procedure, is implemented to the synthesis of conformal slot arrays that reside on a perfectly conducting elliptic cone. In the design scheme, coupling between the slots is taken into account. The coupling information is derived through a numerically rigorous technique based on a full wave analysis. Two arrays, a circumferential and a quasi-radial, are synthesized. In the design examples, constraints on the side lobe level, on scanning capabilities and on cosecant pattern shaping are included.

A procedure that can be employed to design slot arrays on smooth convex conducting surfaces is presented. The uniform theory of diffraction (UTD) for the analysis and the orthogonal method (OM) for the synthesis have been used. Detailed description of the method is given and it is accompanied by a design study of a slot array on a perfectly conducting paraboloid. UTD has been applied after a proper re-construction and re-evaluation of the diffraction integral. Thus, a method for treatment of caustics formed on convex surfaces comes out as a by-product of our study. Coupling phenomena between two slots on convex surfaces are also addressed.

This work aims at the establishment of a methodology providing the characteristic modes of mobile devices realistic models including their metallic parts as well as their material-dielectric loading. A modified integral equation Moment method is employed to yield the impedance matrix of such metal-dielectric structures. In turn the characteristic mode approach is employed to formulate and solve the related eigenproblem.

A comprehensive study on the statistics of adaptive antenna arrays is presented. The main contribution is the derivation of the probability distribution function of the cochannel interference for the uplink of mobile communications systems, unconditioned on the interferers' directions of arrival. Closed-form results for the cumulative distribution function, moment generating function, and outage probability are also reported. Numerical verification is provided, utilizing both simulation and published data. Copyright © 2011 John Wiley & Sons, Ltd.

Our activity has to do with the design of Direct Radiating Arrays (DRA) for satellite communications. The objective is to have a reduced number of controls in order to minimize the manufacturing and operating complexity. The DRAs will create a set of simultaneously overlapped multi-beams in the frequency range of 20 GHz and will satisfy certain specifications (End of Coverage (EOC) gain, grating and side lobe levels). Radio-Communications Laboratory (RCL) shall consider the DRA design and shall mainly optimize the geometry of the array and develop the appropriate software tool. The design methods which are going to be used are the Fractal Technique and the Orthogonal Method(OM) in conjunction with the Orthogonal Perturbation Method (OPM). Some preliminary examples are presented and show the effectiveness of the design methods.

A Neural Network (NN) methodology is presented for the Direction of Arrival (DoA) estimation of the desired mobile user, namely the Signal of Interest (SoI), in the asynchronous Direct Sequence Code Division Multiple Access (DS-CDMA) scheme. In DS-CDMA the SoI DoA should be estimated in the presence of a group of interfering users that constitute the Multiple Access Interference (MAI). In this paper a NN algorithm follows the MAI suppression done by the code-matched filters, to achieve the DoA finding goal for a Switched-Beam System (SBS). The proposed method is developed, while DoA estimation simulation tests show accurate results for a varying number of mobile users., Prikazana je metodologija procjene smjera dolaska signala željenog pokretnog korisnika uz primjenu neuralnih mreža za sustave s višestrukim pristupom po kodnoj osnovi s asinkronom izravnom sekvencijom (DS-CDMA). U sustavima DS-CDMA, valja procijeniti smjer dolaska signala željenog korisnika u nazočnosti više korisnika koji stvaraju interferencije (smetnje) što vodi do interferencije višestrukog pristupa. U ovom se radu rabi algoritam neuralnih mreža za potiskivanje interferencije uz primjenu kodno prilagodenih filtara kako bi se mogao odrediti smjer dolaska signala u sustavu s preklapanjem antenskog snopa. Razvijena je predložena metoda, a simulacijski pokusi s procjenom smjera dolaska signala pokazali su točne rezultate za različit broj pokretnih korisnika.

Presentation of a geometry synthesis procedure accompanied by the Orthogonal Method employed for arrays on various non-planar surfaces is given in the work at hand. Prior to the enforcement of the design procedure the host's response is analyzed so that radiation from the element radiators are characterised. Afterwards, radiation information is used in the design technique to synthesize an array with the desired response specifications. We start from an initial conformal array and we perturb the element positions by combining an iterative technique with the orthogonal method. The final position of the elements is found from the last iteration where the desired approximation of the pattern is obtained. It is noticed that our formulation does not give always a successful outcome, since the search can be trapped in a local minimum. Thus, the successful issue comes from a suitable selection of the initial array. Also, in many cases the procedure could be repeated for non-uniform excitations if the final result does not give the desired approximation. Several examples for conformal arrays on circular cylinders, on paraboloids and on elliptic cones for different cases will show the applicability of the orthogonal method. (6 pages)

A new direction of arrival (DoA) estimation method using neural networks (NNs) is presented. The method is especially designed for a switched-beam system (SBS) that operates in an asynchronous direct sequence code division multiple access (DS-CDMA) scheme. The technique exploits the Multiple Access Interference (MAI) suppression done by the code-matched filters in DS-CDMA, and is simple and appropriate for real time applications. Simulations of DoA estimations tests show accurate results for a varying number of interferers.

Summary form only given. Conformal antenna arrays are well suited to radar and communication applications. A cylindrical microstrip antenna array due to the lightweight, low-profile, low cost, integrability with microwave circuitry and simple manufacturing is an attractive choice among other systems. In order to analyze and eventually exploit such geometries, suitable modeling tools, other than the ones used for planar arrays, are needed. These tools must be able to synthesize the array and analyze the whole system, including mutual coupling. In this study we focus our effort in developing a stable and computationally effective tool that takes into account the coupling between the element radiators. Such an effort has to cope with the evaluation of Sommerfeld-type integrals and the Bessel-type Green's function. The patch antenna modeling is treated by using the surface-current model. The key assumption is that the patch metalization is replaced by a surface electric current density, which is unknown and needs to be found. The Green's function of the coated cylindrical conductor is expressed as an infinite sum of Bessel functions. The mutual coupling is found by combining method of moments with the reaction theorem for the near zone EM field of the patches. The far field is acquired via the inverse Fourier transform using the steepest decent method of integration. Mutual coupling computations as a function of frequency, of the angular separation and the cylinder radius are presented and compared with results coming from the international literature. These results show the reasonable agreement and the validation of our numerical code.

Water scarcity and desertification are considered to be among the greatest challenges of humanity over the coming decades. Worldwide, agriculture accounts to 69% of total water usage, while industry accounts for 23%, and urban use to 8%. In Greece, a rural development model and poor farming practices have resulted in an overwhelming 83% of total water consumption to be directed to farming uses. Furthermore, excessive use of water in agriculture combined with existing pesticides and fertilizers usage levels creates exponential problems in the water cycle in Greece. Taking into account the above challenges, the AREThOU5A Project aims to exploit the state-of-the-art technologies and, in particular, the emerging developments in the field of Internet of Things (IoT) as a means to promote rational use of water resources in agriculture. In particular, AREThOU5A Project aims at accelerating penetration of low-power wide-access (LPWA) technologies through a series of research and innovation actions focusing on the design, development, operation and commercial exploitation of relevant hardware/software & IoT applications. Preliminary results of the AREThOU5A Project are depicted and future remarks are outlined.