Contribución al análisis eficiente y a la mejora de prestaciones de antenas reflectarray

El diseño de una antena reflectarray bajo la aproximación de periodicidad local requiere la determinación de la matriz de scattering de estructuras multicapa con metalizaciones periódicas para un gran número de geometrías diferentes. Por lo tanto, a la hora de diseñar antenas reflectarray en tiempos de CPU razonables, se necesitan herramientas númericas rápidas y precisas para el análisis de las estructuras periódicas multicapa. En esta tesis se aplica la versión Galerkin del Método de los Momentos (MDM) en el dominio espectral al análisis de las estructuras periódicas multicapa necesarias para el diseño de antenas reflectarray basadas en parches apilados o en dipolos paralelos coplanares. Desgraciadamente, la aplicación de este método numérico involucra el cálculo de series dobles infinitas, y mientras que algunas series convergen muy rápidamente, otras lo hacen muy lentamente. Para aliviar este problema, en esta tesis se propone un novedoso MDM espectral-espacial para el análisis de las estructuras periódicas multicapa, en el cual las series rápidamente convergente se calculan en el dominio espectral, y las series lentamente convergentes se calculan en el dominio espacial mediante una versión mejorada de la formulación de ecuaciones integrales de potenciales mixtos (EIPM) del MDM. Esta versión mejorada se basa en la interpolación eficiente de las funciones de Green multicapa periódicas, y en el cálculo eficiente de las integrales singulares que conducen a los elementos de la matriz del MDM. El novedoso método híbrido espectral-espacial y el tradicional MDM en el dominio espectral se han comparado en el caso de los elementos reflectarray basado en parches apilados. Las simulaciones numéricas han demostrado que el tiempo de CPU requerido por el MDM híbrido es alrededor de unas 60 veces más rápido que el requerido por el tradicional MDM en el dominio espectral para una precisión de dos cifras significativas. El uso combinado de elementos reflectarray con parches apilados y técnicas de optimización de banda ancha ha hecho posible diseñar antenas reflectarray de transmisiónrecepción (Tx-Rx) y polarización dual para aplicaciones de espacio con requisitos muy restrictivos. Desgraciadamente, el nivel de aislamiento entre las polarizaciones ortogonales en antenas DBS (típicamente 30 dB) es demasiado exigente para ser conseguido con las antenas basadas en parches apilados. Además, el uso de elementos reflectarray con parches apilados conlleva procesos de fabricación complejos y costosos. En esta tesis se investigan varias configuraciones de elementos reflectarray basadas en conjuntos de dipolos paralelos con el fin de superar los inconvenientes que presenta el elemento basado en parches apilados. Primeramente, se propone un elemento consistente en dos conjuntos apilados ortogonales de tres dipolos paralelos para aplicaciones de polarización dual. Se ha diseñado, fabricado y medido una antena basada en este elemento, y los resultados obtenidos para la antena indican que tiene unas altas prestaciones en términos de ancho de banda, pérdidas, eficiencia y discriminación contrapolar, además de requerir un proceso de fabricación mucho más sencillo que el de las antenas basadas en tres parches apilados. Desgraciadamente, el elemento basado en dos conjuntos ortogonales de tres dipolos paralelos no proporciona suficientes grados de libertad para diseñar antenas reflectarray de transmisión-recepción (Tx-Rx) de polarización dual para aplicaciones de espacio por medio de técnicas de optimización de banda ancha. Por este motivo, en la tesis se propone un nuevo elemento reflectarray que proporciona los grados de libertad suficientes para cada polarización. El nuevo elemento consiste en dos conjuntos ortogonales de cuatro dipolos paralelos. Cada conjunto contiene tres dipolos coplanares y un dipolo apilado. Para poder acomodar los dos conjuntos de dipolos en una sola celda de la antena reflectarray, el conjunto de dipolos de una polarización está desplazado medio período con respecto al conjunto de dipolos de la otra polarización. Este hecho permite usar solamente dos niveles de metalización para cada elemento de la antena, lo cual simplifica el proceso de fabricación como en el caso del elemento basados en dos conjuntos de tres dipolos paralelos coplanares. Una antena de doble polarización y doble banda (Tx-Rx) basada en el nuevo elemento ha sido diseñada, fabricada y medida. La antena muestra muy buenas presentaciones en las dos bandas de frecuencia con muy bajos niveles de polarización cruzada. Simulaciones numéricas presentadas en la tesis muestran que estos bajos de niveles de polarización cruzada se pueden reducir todavía más si se llevan a cabo pequeñas rotaciones de los dos conjuntos de dipolos asociados a cada polarización. ABSTRACT The design of a reflectarray antenna under the local periodicity assumption requires the determination of the scattering matrix of a multilayered structure with periodic metallizations for quite a large number of different geometries. Therefore, in order to design reflectarray antennas within reasonable CPU times, fast and accurate numerical tools for the analysis of the periodic multilayered structures are required. In this thesis the Galerkin’s version of the Method of Moments (MoM) in the spectral domain is applied to the analysis of the periodic multilayered structures involved in the design of reflectarray antennas made of either stacked patches or coplanar parallel dipoles. Unfortunately, this numerical approach involves the computation of double infinite summations, and whereas some of these summations converge very fast, some others converge very slowly. In order to alleviate this problem, in the thesis a novel hybrid MoM spectral-spatial domain approach is proposed for the analysis of the periodic multilayered structures. In the novel approach, whereas the fast convergent summations are computed in the spectral domain, the slowly convergent summations are computed by means of an enhanced Mixed Potential Integral Equation (MPIE) formulation of the MoM in the spatial domain. This enhanced formulation is based on the efficient interpolation of the multilayered periodic Green’s functions, and on the efficient computation of the singular integrals leading to the MoM matrix entries. The novel hybrid spectral-spatial MoM code and the standard spectral domain MoM code have both been compared in the case of reflectarray elements based on multilayered stacked patches. Numerical simulations have shown that the CPU time required by the hybrid MoM is around 60 times smaller than that required by the standard spectral MoM for an accuracy of two significant figures. The combined use of reflectarray elements based on stacked patches and wideband optimization techniques has made it possible to design dual polarization transmit-receive (Tx-Rx) reflectarrays for space applications with stringent requirements. Unfortunately, the required level of isolation between orthogonal polarizations in DBS antennas (typically 30 dB) is hard to achieve with the configuration of stacked patches. Moreover, the use of reflectarrays based on stacked patches leads to a complex and expensive manufacturing process. In this thesis, we investigate several configurations of reflectarray elements based on sets of parallel dipoles that try to overcome the drawbacks introduced by the element based on stacked patches. First, an element based on two stacked orthogonal sets of three coplanar parallel dipoles is proposed for dual polarization applications. An antenna made of this element has been designed, manufactured and measured, and the results obtained show that the antenna presents a high performance in terms of bandwidth, losses, efficiency and cross-polarization discrimination, while the manufacturing process is cheaper and simpler than that of the antennas made of stacked patches. Unfortunately, the element based on two sets of three coplanar parallel dipoles does not provide enough degrees of freedom to design dual-polarization transmit-receive (Tx-Rx) reflectarray antennas for space applications by means of wideband optimization techniques. For this reason, in the thesis a new reflectarray element is proposed which does provide enough degrees of freedom for each polarization. This new element consists of two orthogonal sets of four parallel dipoles, each set containing three coplanar dipoles and one stacked dipole. In order to accommodate the two sets of dipoles in each reflectarray cell, the set of dipoles for one polarization is shifted half a period from the set of dipoles for the other polarization. This also makes it possible to use only two levels of metallization for the reflectarray element, which simplifies the manufacturing process as in the case of the reflectarray element based on two sets of three parallel dipoles. A dual polarization dual-band (Tx-Rx) reflectarray antenna based on the new element has been designed, manufactured and measured. The antenna shows a very good performance in both Tx and Rx frequency bands with very low levels of cross-polarization. Numerical simulations carried out in the thesis have shown that the low levels of cross-polarization can be even made smaller by means of small rotations of the two sets of dipoles associated to each polarization

The contribution of Julien Perruisseau-Carrier to reconfigurable reflectarray antennas

An invited talk on the Contribution of Julien Perruisseau-Carrier to Reconfigurable Reflectarray Antennas

Enhanced integral equation analysis of multilayered periodic structures useful for the design of reflectarray antennas

When reflectarray antennas are designed under the local periodicity assumption, the problem of the scattering of plane waves by multilayered pe- riodic structures has to be solved many times. The Method of oments (MoM) in the spectral domain is the numerical technique usually employed for the analysis of these multilayered structures. Unfortu- nately, it is not computationally efficient since it requires the determination of slowly convergent dou- ble infinite summations. In this paper the Mixed Potential Integral Equation (MPIE) formulation of the MoM in the spatial domain is invoked to transform the slowly convergent summations into singular finite double integrals that can be efficiently computed. The novel MoM approach in the spatial do- main has been found to be between one and two orders of magnitude faster than the traditional spectral domain MoM both in the analysis of multilay- ered periodic structures, and in the design of reflecflectarray antennas with cell characterization based on the local periodicity assumption

Reflectarray antennas for dual polarization and broadband telecom satellite applications

A reflectarray antenna with improved performance is proposed to operate in dual-polarization and transmit-receive frequencies in Ku-band for broadcast satellite applications. The reflectarray element contains two orthogonal sets of four coplanar parallel dipoles printed on two surfaces, each set combining lateral and broadside coupling. A 40-cm prototype has been designed, manufactured, and tested. The lengths of the coupled dipoles in the reflectarray cells have been optimized to produce a collimated beam in dual polarization in the transmit and receive bands. The measured radiation patterns confirm the high performance of the antenna in terms of bandwidth (27%), low losses, and low levels of cross polarization. Some preliminary simulations at 11.95 GHz for a 1.2-m antenna with South American coverage are presented to show the potential of the proposed antenna for spaceborne antennas in Ku-band

Aplicación del método de los momentos al análisis de estructuras periódicas multicapa 2-D: comparación entre las versiones espectral y espacial

In this paper the authors apply the Method of Moments (MoM) to the analysis of the scattering of a multilayered periodic strip grating by a plane wave with oblique incidence and arbitrary polarization. The problem is initially solved by means of the MoM in the spectral domain. However, since this approach leads to the computation of slowly convergent series, the problem is also solved by using a mixed potential integral equation (MPIE) formulation of the MoM in the spatial domain. Thanks to the efficient computation of the periodic potentials Green?s functions and thanks to the closed-form integration of part of the integrals involved in the MoM matrix entries, important CPU time savings are attained when applying the MoM in the spatial domain. In fact, the implemented spatial domain version of the MoM turns out to be one order of magnitude faster than the spectral domain version when basis functions that account for edge singularities are used in the modeling of the current density on the metallizations

Dual-polarization transmit-receive reflectarray antenna made of cells with two orthogonal sets of coplanar parallel dipoles

A dual-polarization dual frequency focused beam reflectarray antenna is designed for transmit-receive (Tx-Rx) operation in Ku Band. A novel broadband reflectarray element is introduced, which consists of two orthogonal sets of three parallel dipoles. To adjust the dimensions of the elements in the antenna, we have used the local periodicity assumption, and we have analyzed a multilayered periodic structure surrounding each element by means of a home-made software based on the method of moments in the spectral domain. This strategy makes it possible to design reflectarray antennas within reasonable CPU times. The designed antenna shows a bandwidth of 10.9% in Tx-band and 7.1% in Rx-band for gain variations lower than 1 dB. Also, levels of cross-polar components 30 dB below the radiation maximum have been achieved. In order to improve the crosspolar discrimination, the elements of the designed reflectarray have been slightly rotated, and this has made it possible to achieve levels of cross-polar components 35 dB below the maximum in both the Tx and the Rx band

Design of a reflectarray antenna at 300 GHz based on cells with three coplanar dipoles

Simulated results are presented for a reflectarray antenna designed to produce a collimated beam at 300 GHz within a 13% bandwidth. The reflectarray cells are made of three parallel dipoles printed on one side of a 110-μm Quartz wafer coated with a conductive ground plane on the back side, where the phase is adjusted by varying the length of the dipoles. A practically linear phase variation is achieved in a range greater than 360° and frequencies from 280 GHz to 320 GHz. A reflectarray antenna was designed taking into account the angle of incidence and the polarization of the incident field. The simulated radiation patterns show a fixed collimated beam with variations in gain lower than 2.6 dB within a 13% bandwidth

Improvements in the MoM analysis of 2-D planar multilayered periodic structures

In this paper the authors apply the Method of Moments (MoM) to the analysis of the scattering of a multilayered periodic strip grating by a plane wave with oblique incidence and arbitrary polarization. It is shown that the use of an improved MoM spatial domain approach is one order of magnitude faster than the use of the classical MoM spectral domain approach when basis functions that account for edge singularities are used in the modeling of the current density on the metallizations

Efficient MoM analysis of multilayered periodic arrays of stacked rectangular patches. Application in the design of reflectarray antennas

Reflectarray antennas are an interesting alternative to reflector antennas for satellite broadcast and telecommunications missions owing to their reduced mass and volume, low cost, improved polarization performance, etc

Efficient analysis of multi-resonant periodic structures for the improved analysis and design of reflectarray antennas

In order to design reflectarray antennas within reasonable CPU times, fast and accurate numerical tools for the analysis of periodic multilayered structures are required. In this paper the method of moments in the spectral domain (MoMSD) based on multilayered Green's functions (MGF) is applied to the analysis of periodic structures containing multilayered stacked patches in the unit cell. These multiresonant cells are potential elements for the design of reflectarray antennas. In the paper we show that the use of basis functions with edge singularities in the approximation of the current density on the patches leads to important computer memory and CPU time savings in the analysis of the periodic structures. Also, a rational fitting technique is introduced which makes it possible to obtain closed-form expressions for the scattering matrix of the periodic structures in terms of the dimension of the patches used to adjust the phase of the reflectarray elements