Circuitos de microondas uniplanares multimodales, reconfigurables

Resumo

The complexity of high-frequency systems is increasing every day as a consequence of the required performances. This is the case for scientific instruments which are part of satellite payloads and require high precision and resolution. Other requirements have to be added to the electrical performances of the system, such as low power consumption, weight and cost. In this context, the classical design methodologies have to be substituted in order to reach these new set of specifications. One way to proceed is to develop new design techniques and technologies. This Thesis proposes to use the different modes that can be propagated in uniplanar transmission lines (CPW even and odd modes, and slotline mode). To enable a systematic procedure for circuit analysis and design, accurate multimodal models are used which take into account all the modal interactions and separates the CPW even and odd modes. As a result, an alternative design method to achieve more compact and broadband high-frequency circuits is proposed. Multimodal models provide insight into CPW circuits under general even- and odd-mode excitations, and understanding of their response to arbitrary loading conditions (which can in general be different for the even and odd modes). When available, they constitute a reasonable alternative, from a circuit point of view, to the more time-consuming full wave EM. In order to design the multimodal uniplanar circuits proposed in this Thesis, it is necessary to understand each of the different types of transmission lines used and their different propagation modes. In this work, modelling of different uniplanar transmission lines (CPW and slotline transmission lines) is presented from a multimodal point of view. Another important added value in high-frequency circuits is reconfigurability. RF- MEMS (MicroElectroMechanical Systems) technology has demonstrated a great potential for reconfigurability purposes, especially at microwave and millimetre bands. The reconfigurability of some of the circuits proposed in this Thesis will be done by means of RF-MEMS switches. However, the electrical modelling of RF-MEMS switches poses new challenges. Indeed, the switch electrical performance is coupled to the mechanical properties of the structures and materials involved in its implementation and also to the fabrication process technology. Furthermore, although RF-MEMS switches are 3D structures, they can also be considered 2.5D structures due to their very high aspect ratio. Electrical modelling can then be addressed by a great variety of 3D or 2.5D EM simulation tools. This work proposes different strategies for the electrical modelling of capacitive and resistive RF-MEMS switches which take into account the dependence of the device electrical performance on the mechanical properties and technological processes. Finally, a number of uniplanar multimodal reconfigurable circuits, based on the techniques previously developed, are proposed, designed and characterized. More specifically, a number of new topologies to implement two different applications are developed: 180º hybrids and 0º/180º phase switches. The circuits are presented along with their design procedure (based on circuital multimodal models). The final goal is to demonstrate that using both multimodal design techniques and RF-MEMS technology it is possible to implement high-frequency circuits with advanced performances. The proposed circuits have low power consumption, low insertion loss and a high degree of miniaturization (mainly due to the characteristics of RF MEMS switches). Using the multimodal property of uniplanar transmission lines, the proposed structures result also more compact and broadband, especially in terms of phase. The designed circuits feature similar or better results than the state of the art.