Análisis y diseño de filtros compactos de microondas basados en cristales electromagnéticos y resonadores metamateriales

Abstract

[SPA] Esta tesis doctoral se presenta bajo la modalidad de compendio de publicaciones. La presente tesis está centrada en el análisis y síntesis de dispositivos de microondas. Más concretamente, se han desarrollado tres tipos de celdas basadas en estructuras metamateriales, las cuales se han aplicado en el diseño original de filtros compactos en tecnología planar (línea microtira, guía coplanar y guía de onda integrada en sustrato, SIW). Las celdas y dispositivos propuestos pueden ser de un gran interés para los futuros sistemas de comunicación. Por un lado, la tecnología planar es un método de fabricación maduro y de bajo coste y, por otro lado, los dispositivos basados en estructuras metamateriales presentan propiedades electromagnéticas singulares, que permiten reducir el tamaño y superar las limitaciones de los dispositivos convencionales. Entre los diferentes metamateriales que existen, se utilizaron los pertenecientes a los cristales electromagnéticos (Electromagnetic Band Gap, EBG) y a los medios de Veselago. Los EBG convencionales son estructuras con una única fila de patrones circulares periódicos, grabados en el plano de masa de una línea microtira. Estas estructuras exhiben bandas de frecuencia en las que se permiten y se impiden la propagación electromagnética. Este comportamiento es conocido como reflector de Bragg. Las estructuras EBG propuestas sustituyen los patrones circulares por celdas basadas en geometrías fractales de Koch (KFEBG), creadas a partir de una configuración hexagonal. Estas celdas KFEBG permiten superar el límite constructivo radio-periodo (r/a) en EBG convencionales, definido en 0.45. Cuando r/a < 0.5, la estructura microtira-KFEBG presenta el mismo comportamiento que una estructura microtira-EBG convencional (reflector de Bragg), mientras que cuando r/a > 0.5, la estructura microtira-KFEBG presenta una amplia banda de rechazo, inusual para este tipo de configuración. Por ello, se aplicó la estructura periódica KFEBG con r/a > 0.5 en el diseño de filtros compactos paso-bajo en tecnologías microtira y SIW. Para mejorar la respuesta en frecuencia y reducir el tamaño de estos filtros, se realizó una apodización modulada de los parámetros de diseño. Finalmente, se desarrolló un método de síntesis original para lograr estos diseños. Por otro lado, los medios de Veselago, también conocidos como materiales zurdos (Left-Handed, LH), se caracterizan por poseer partes reales de permitividad y de permeabilidad simultáneamente negativas. En ellos, es posible la propagación de ondas regresivas entre otros fenómenos inusuales. Las configuraciones iniciales están basadas en resonadores de anillos (celdas) SRR y CSRR (Split ring resonator, Complementary Split ring resonator), acoplados a una línea de transmisión. A posteriori, se desarrollaron las versiones abiertas OSRR (Open Split ring resonator) y OCSRR (Open Complementary Split ring resonator) que permiten una conexión directa con la línea de transmisión, una mayor facilidad de diseño de dispositivos y un tamaño reducido con respecto a los SRR y CSRR. En este trabajo, se propone dos celdas basadas en resonadores de anillos abiertos: la OISRR (Open Interconnected Split Ring Resonator) de tipo mono-planar como las anteriores y la DOSRR (Double- Sided Open Split Ring Resonator) de tipo bi-planar con parámetros de diseño en dos planos diferentes. Ambas celdas poseen un tamaño reducido como la OSRR y características interesantes. Las celdas DOSRR y OISRR se aplicaron, respectivamente, al diseño en tecnología planar de filtros compactos pasobanda con altos niveles de rechazo y filtros compactos rechazo-banda de alta selectividad (notch). [ENG] This thesis focuses on the analysis and synthesis of microwave devices. More specifically, three types of cell structures metamaterials have been developed. They have been applied to the original design of compact filters in planar technology (microstrip, coplanar waveguide CPW and substrate integrated waveguide SIW). The proposed cells and devices may be of great interest for future communication systems. On the one hand, the planar technology is a mature and low cost method of manufacturing, and on the other hand, the devices based on metamaterial structures show unique electromagnetic properties which will make possible reducing the size and overcoming the limitations of conventional devices. Among the different metamaterials existing, we used those belonging to electromagnetic crystals (Electromagnetic Band Gap, EBG) and Veselago media. Conventional EBGs in microstrip technology are a periodic structure with one row of circular patterns etched on the ground plane. This structure exhibits bands of frequencies in which electromagnetic propagation is not allowed as a Bragg reflector. EBG structures proposed changing the circular patterns by cells based on fractal geometry Koch (KFEBG), created from a hexagonal shape. KFEBG cells allow the realization of structure with r/a (radii/period) ratio higher than 0.45 (which is the upper limit of the conventional 1-D EBG structure). When r/a <0.5, the microstrip-KFEBG structure has the same behavior as a conventional microstrip-EBG structure (Bragg reflector), however when r/a > 0.5, the microstrip- KFEBG structure presents a wide stopband, unusual on this kind of configuration. Therefore, the periodic structure KFEBG is applied to r/a> 0.5 in the design of compact low-pass filters in microstrip technology and SIW. In order to improve the frequency response and reduce the size of these filters, a modulated apodization of the design parameters was performed. And finally, an original synthesis method to achieve these designs is developed. Furthermore, Veselago media, also called left-handed materials (LH), are characterized by real parts of permittivity and permeability negative simultaneously. These media make possible the spread of regressive waves among other unusual phenomena. First cells are based on split ring resonators (SRR) and complementary split ring resonators (CSRR) coupled to a transmission line. Later, the open versions OSRR (Open Split ring resonator) and OCSRR (Open Complementary Split ring resonators) are developed; these cells allow direct connection to the transmission line, a greater ability to design devices and a reduced size compared to SRR and CSRR cells. In this work, two new cells based on open rings resonators are presented, OISRR (Open Interconnected Split Ring Resonator) is a mono-planar cell as above and DOSRR (Double- Sided Open Split Ring Resonator) is a bi-planar cell with design parameters in two different planes. Both cells have a reduced size like OSRR and show interesting features. The DOSRR and OISRR cells were applied to the design in planar technology of compact band-pass filters with high levels of rejection and high selectivity compact stop-band filters (notch), respectively.

[ENG] This doctoral dissertation has been presented in the form of thesis by publication.This thesis focuses on the analysis and synthesis of microwave devices. More specifically, three types of cell structures metamaterials have been developed. They have been applied to the original design of compact filters in planar technology (microstrip, coplanar waveguide CPW and substrate integrated waveguide SIW). The proposed cells and devices may be of great interest for future communication systems. On the one hand, the planar technology is a mature and low cost method of manufacturing, and on the other hand, the devices based on metamaterial structures show unique electromagnetic properties which will make possible reducing the size and overcoming the limitations of conventional devices. Among the different metamaterials existing, we used those belonging to electromagnetic crystals (Electromagnetic Band Gap, EBG) and Veselago media. Conventional EBGs in microstrip technology are a periodic structure with one row of circular patterns etched on the ground plane. This structure exhibits bands of frequencies in which electromagnetic propagation is not allowed as a Bragg reflector. EBG structures proposed changing the circular patterns by cells based on fractal geometry Koch (KFEBG), created from a hexagonal shape. KFEBG cells allow the realization of structure with r/a (radii/period) ratio higher than 0.45 (which is the upper limit of the conventional 1-D EBG structure). When r/a <0.5, the microstrip-KFEBG structure has the same behavior as a conventional microstrip-EBG structure (Bragg reflector), however when r/a > 0.5, the microstrip- KFEBG structure presents a wide stopband, unusual on this kind of configuration. Therefore, the periodic structure KFEBG is applied to r/a> 0.5 in the design of compact low-pass filters in microstrip technology and SIW. In order to improve the frequency response and reduce the size of these filters, a modulated apodization of the design parameters was performed. And finally, an original synthesis method to achieve these designs is developed. Furthermore, Veselago media, also called left-handed materials (LH), are characterized by real parts of permittivity and permeability negative simultaneously. These media make possible the spread of regressive waves among other unusual phenomena. First cells are based on split ring resonators (SRR) and complementary split ring resonators (CSRR) coupled to a transmission line. Later, the open versions OSRR (Open Split ring resonator) and OCSRR (Open Complementary Split ring resonators) are developed; these cells allow direct connection to the transmission line, a greater ability to design devices and a reduced size compared to SRR and CSRR cells. In this work, two new cells based on open rings resonators are presented, OISRR (Open Interconnected Split Ring Resonator) is a mono-planar cell as above and DOSRR (Double- Sided Open Split Ring Resonator) is a bi-planar cell with design parameters in two different planes. Both cells have a reduced size like OSRR and show interesting features. The DOSRR and OISRR cells were applied to the design in planar technology of compact band-pass filters with high levels of rejection and high selectivity compact stop-band filters (notch), respectively.