George S. Miaris

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.

On the quantized excitation and the geometry synthesis of a linear array by the orthogonal method

A method for the geometry synthesis of a linear array is presented. We start from an initial array with quantized amplitudes. After this, 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. Arrays with more constraints on the pattern need more quantized amplitudes. Several examples for different cases show the applicability of our method.

The orthogonal method for the geometry synthesis of a linear antenna array

The orthogonal method for geometry synthesis of a linear antenna array is presented. We start from an initial array, and we perturb the element positions by using an iterative procedure and applying the orthogonal method. Applications for arrays with uniform excitation give patterns with the desired sidelobe level.

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.

Pyramidal-horn design under constraints on half-power beamwidth

A pyramidal-horn design is presented. Two distinct design cases are considered. The first one uses the half-power beamwidth in the two principal planes as a constraint, while the second uses the ratio of the half-power beamwidths and the directivity of the horn. A number of approximate expressions make the procedure simple. Some characteristic examples show the applicability of the method.

Orthogonal Advanced Methods for Antennas: the ORAMA computer tool

A computer tool (ORAMA) for the synthesis of linear antenna arrays is presented. The orthogonal method (OM) and the orthogonal perturbation (OP) method are used. The orthogonal method derives the excitation of the elements of the array, while the orthogonal perturbation method quantizes the excitation and determines the position of the elements. The user has the options to select the array geometry, the case study for a specific desired pattern, the method to be used, and the element type. Several design cases with various constraints are presented. ORAMA (a demo of the software is available at http://rcl.physics.auth.gr) has been designed as a Windows MDI application for the academic classroom, as well as for professional antenna engineers. A set of examples for different array patterns shows the usefulness of the tool.

A unified formulation for Chebyshev and Legendre superdirective endfire array design

ContentsA unified formulation for superdirective end-fire arrays by using Chebyshev and Legendre Polynomials and their maximum directivities as well as the corresponding efficiency index and theQ factor are found. Several examples show the simplicity of the formulation.ÜbersichtEs wird eine einheitliche Formulierung für Supergain-Längsstrahler mit Tschebyscheff- und Legendre-Polynomen vorgestellt. Die Strahlergruppen werden für unterschiedliche Kombinationen dieser Polynome angegeben, ebenso ihre optimalen Richtgewinne wie auch der dazugehörige Strahlungs- Wirkungsgrad in der Hauptrichtung und der GütefaktorQ. Einige Beispiele belegen die Einfachheit der Formulierung.

On mobile communications smart base-station system design

A design technique for mobile base-station antennas is presented. Beam tilting to avoid intersymbol interference is considered, and the orthogonal method (OM) under constraints on the radiation pattern is applied. The adaptive architecture of the mobile system, in conjunction with the direction of arrival (DoA) and the least mean square algorithms, is explained. A set of useful examples shows the applicability of the whole design.

On the Orthogonal Nonuniform Synthesis From a Set of Uniform Linear Arrays

Synthesis of uniform linear arrays by using the orthogonal method is presented. Composing functions similar to that of Woodward-Lawson technique are used. In Woodward-Lawson technique, sampling of the desired pattern is made. In this letter, instead of sampling, the orthogonal method is applied. The number of composing functions can be the same as or different than the elements of the arrays. Also, the progressive phase of each function can be derived in several ways. Numerical examples for the synthesis of different array patterns are presented, and the results show the usefulness of the method.

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.