Dr. Daniel Rodríguez Prado

Jesús Alberto López-Fernández

Fast and Accurate Modeling of Dual-Polarized Reflectarray Unit Cells Using Support Vector Machines

George Goussetis

A machine learning technique is applied to the design and optimization of reflectarray antennas to considerably accelerate computing time without compromising accuracy. In particular, Support Vector Machines (SVMs), automatic learning structures that are able to deal with regression problems, are employed to obtain surrogate models of the reflectarray element to substitute the full-wave analysis tool for the characterization of the unit cell in the design and optimization algorithms. The analysis, design and optimization of a very large reflectarray antenna for Direct Broadcast Satellite applications are accelerated up to three orders of magnitude. This is here demonstrated with three examples: one showing the design of a reflectarray; and two for the crosspolar optimization, one with one coverage for each linear polarization (Europe and the Middle East) and another with a Middle East coverage working in dual-linear polarization. The accuracy of the proposed approach is validated by means of a comparison of the final designs with full-wave simulations based on local periodicity obtaining good agreement. The crosspolar dicrimination and crosspolar isolation are greatly improved using the SVMs while considerably reducing computing time.

5 January 2018 in IEEE Transactions on Antennas and Propagation

Journal Article

Jesus A. Lopez-Fernandez

Guillermo Barquero

Efficient Crosspolar Optimization of Shaped-Beam Dual-Polarized Reflectarrays Using Full- Wave Analysis for the Antenna Element Characterization

Fernando Las-Heras

This paper describes the characterization of reflectarray unit cells using support vector machines (SVMs) to obtain fast and accurately the full matrix of reflection coefficients, which is used for an analysis of dual-polarized reflectarrays, demonstrating the performance of the model. First, a surrogate model of the reflectarray unit cell is obtained using SVMs. To this end, a set of random samples of the reflection coefficient matrix with a full-wave method of moments based on local periodicity (MoM-LP) is used to train the SVMs. To efficiently obtain the surrogate model, a novel strategy to accelerate the training process is presented, remarkably reducing computing time. Next, the model is tested against a different set of samples, obtaining an excellent agreement between the SVM model and MoM-LP simulations for all reflection coefficients, including the cross-coefficients. The surrogate model is then used for an efficient analysis of three reflectarrays with pencil beam for point-to-point communications, isoflux pattern for global Earth coverage, and a shaped beam for local multipoint distribution service application, showing excellent agreement in both copolar and crosspolar patterns between the SVM and MoM-LP simulations. Finally, the analysis is accelerated by a factor larger than three orders of magnitude using SVMs instead of MoM-LP.

1 December 2016 in IEEE Transactions on Antennas and Propagation

Journal Article

Manuel Arrebola

Wideband Shaped-Beam Reflectarray Design Using Support Vector Regression Analysis

Rafael Florencio

Rafael R. Boix

Fernando Las-Heras

A method for the optimization of the crosspolar component of dual-polarized reflectarrays using full-wave analysis at the element level is described and demonstrated. The reflectarray full-wave analysis is based on local periodicity (LP) and integrated within the optimization process in order to accurately characterize the crosspolar far field. The proposed method is based on the generalized Intersection Approach framework using the Levenberg-Marquardt Algorithm as backward projector, and the employed full-wave analysis is based on the Method of Moments assuming Local Periodicity (MoM-LP). Several strategies to accelerate the computations are exploited, such as the parallelization of all the algorithm building blocks. To minimize the impact of MoM-LP in the optimization process, a strategy to reduce the number of MoM-LP calls is described, further accelerating the algorithm. Moreover, the convergence is improved by working with the squared field amplitude, alleviating the trap problem of local optimizers. This method allows to optimize the crosspolar component in the whole visible region or only in the coverage zone to facilitate the convergence, reducing computing time and memory usage. Two test cases are provided to validate the technique, one with an isoflux pattern for global Earth coverage and another with European coverage for direct broadcast satellite application.

2 August 2019 in IEEE Antennas and Wireless Propagation Letters

Journal Article

Jesús Alberto López-Fernández

Contoured-Beam Dual-Band Dual-Linear Polarized Reflectarray Design Using a Multiobjective Multistage Optimization

George Goussetis

In recent years, machine learning techniques (MLTs) have been applied to accelerate analysis and design of electromagnetic devices. Algorithms such as artificial neural networks or support vector machines for regression (SVRs) have been proposed for the design of large reflectarrays for space applications at a single frequency. However, multi-frequency optimization of such large antennas has not been tackled with MLTs. In this letter and for the first time, we propose a technique based on the use of SVR analysis to obtain the reflection coefficients to accelerate the design of a very large shaped-beam reflectarray for direct broadcast satellite in a 15% bandwidth. An in-house method of moments based on local periodicity is employed to generate samples to train the SVRs for each considered frequency. Then, the surrogate model is used for a design at central frequency, which is used as starting point for a wideband design procedure that is accelerated more than an order of magnitude without a significant loss of accuracy. It is shown that, by virtue of the proposed methodology, the minimum copolar gain in the coverage zone is improved more than 10dB at the upper frequency while maintaining a computationally efficient design procedure.

1 November 2020 in IEEE Transactions on Antennas and Propagation

Journal Article

General Framework for the Efficient Optimization of Reflectarray Antennas for Contoured Beam Space Applications

George Goussetis

This work presents a dual-band design procedure applied to a very large contoured-beam reflectarray with improved copolar and cross-polarization performances for direct broadcast satellite in dual-band dual-linear polarization. The reflectarray is elliptical, with axes of 1.10 and 1.08 meters, and provides coverage for South America in transmit (11.70GHz–12.20GHz) and receive (13.75GHz–14.25GHz) bands. The novel dual-band design approach is based on the use of a multi-resonant unit cell with several degrees of freedom (DoF). It is divided in several stages to facilitate convergence towards a broadband high-performance reflectarray. First, a narrowband layout is obtained at central frequency with a phase-only synthesis. Then, using a limited number of DoFs, a copolar-only optimization is carried out in both frequency bands maximizing the copolar figure of merit. Finally, increasing the number of DoF, cross-polarization requirements are also included in the optimization procedure. The optimized antenna complies with all copolar and cross-polarization requirements with a loss budget of at least 0.62dB in both receive and transmit bands, outperforming earlier works in the literature while using a smaller antenna than previously proposed for this mission.

19 November 2018 in IEEE Access

Journal Article

Jesús A. López Fernández