Dimitrios G. Babas

Aperiodic Array Layout Optimization by the Constraint Relaxation Approach

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.

EM field measurements in the vicinity of an antenna park for radiation hazard purposes

An extensive set of measurements folr the purpose of mapping of the EM pollution in the vicinity of an Antenna Park is given. The EM power density is compared with three international standard limits. Special attention has been paid to residential areas. An increased EM pollution was found in areas where construction of buildings is planned for the future. In view of these plans, reformation of the park and spreadmg of the antennas have to be done.

A Stochastic Study of Large Arrays Related to the Number of Electrically Large Aperture Radiators

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.

Design of Planar Arrays With Reduced Nonuniform Excitation Subject to Constraints on the Resulting Pattern and the Directivity

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.

Evolutionary design of a dual band E-shaped patch antenna for 5G mobile communications

Fifth generation (5G) wireless technology is a promising solution for multi-Gbps data rates in future mobile communications. The new devices are expected to operate at millimeter wave frequencies. To address the 5G requirements novel antennas have to be developed. In this paper the Teaching-Learning-Optimization (TLBO) algorithm is applied in order to design a dual-band E-shaped patch antenna. The geometrical parameters of the aperture-coupled antenna are the inputs of the optimization algorithm. The method gives acceptable design solutions achieving simultaneously S11 minimization and low VSWR at the frequencies of interest (25GHz and 37GHz).

On the Design of Direct Radiating Antenna Arrays with Reduced Number of Controls for Satellite Communications

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.

Design of radiation-emission measurements of an air-traffic surveillance radar

The current work presents the procedure of designing and carrying out measurements of radiation emission from an air-traffic surveillance radar. The system requirements are first given, and then the equipment used is described. The steps to determine the operating characteristics of the radar are specified in detail. The necessary methods for manual power measurements and calculations are next explained. Since the final measurement system was fully automated, its main features (topology, protocol of operation) are also given. Finally, some measurement results taken during the initial phase of system operation are presented and discussed.

On the synthesis of nonuniform linear microstrip arrays: a circuit design approach

Summary form only given. A synthesis method for the design of non-uniformly spaced series-fed rectangular microstrip arrays is described. By our approach the problem of the patch array design results in one of a slot array synthesis. The resulting equivalent configuration is able to give the necessary parameters for the microstrip array geometry. According to the transmission-line model, which is used in our method, a microstrip antenna can be represented by two radiating slots, separated by a low-impedance, Z/sub 0/, transmission line of length L. When the substrate is thin the equivalent slots are uniformly excited and can be used to derive the necessary expressions for the parameters of the model. Numerical results are given for Taylor, Bayliss and secant square patterns.

Design of overlapping element direct radiating arrays for satellite communications

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 solutions potential.

A software tool for satellite advanced multibeam aperiodic array synthesis

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.