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Structures électromagnétiques à bandes interdites pour des applications de filtre

Heba Badr El-Din El-Shaarawi 1
1 LAAS-MINC - Équipe MIcro et Nanosystèmes pour les Communications sans fil
LAAS - Laboratoire d'analyse et d'architecture des systèmes
Abstract : The increasing development of wireless applications turns out to new requirements for transceiver architectures that have to feature excellent microwave performances (linearity, spurious rejection, noise figure and bandwidth) and enhanced integration density that is achieved through the miniaturization of the modules as well as the introduction of multi standard functionalities. All these requirements translate to the need of filter circuits as miniaturized as possible and featuring the highest performance in term of insertion loss and rejection. Since the late 1980's, electromagnetic bandgap (EBG) structures and defected ground structures (DGS) have attracted the interest of many researchers, due to their interesting properties in terms of size miniaturization, suppression of surface waves and arbitrary stopbands. Since then, they have been used in many applications like lowpass filters, bandpass filters, antennas, waveguides and others. Based on the interesting features proposed by EBG and DGSs, the main aim of this thesis is to achieve miniaturized reconfigurable filters that may serve in wireless communication systems. EBG structures are periodic structures which allow the propagation of electromagnetic waves in certain frequency bands and forbid them in other bands known as the "bandgap". The first step taken towards achieving the goal is to study the state of the art of bandgaps structures, their advantages, disadvantages, applications, and the most important achievements using such structures. Also, a one-dimensional multi-layer periodic structure is studied with two different analytical techniques, the Coupled-Wave Theory and the Bloch-Wave Formalism. Due to the many design parameters of EBG structures, and the difficulty in their modeling, DGS attracted the interest of many researchers as they have the main advantages proposed by EBG structures but by using only one or two cells, in addition, they are easier to model. So the next step in this thesis is to study the different modeling techniques of DGSs. The dumbbell shape DGS is modeled using the parallel LC, parallel RLC, the p-equivalent circuit and others where a comparison between the different models is presented and a conclusion of which is the best suitable to be used in more complex designs. Using the developed models, low-pass filters of order three are designed and simulated on microstrip transmission line and coplanar waveguide technologies. After developing a good understanding of the DGSs, a novel reconfigurable DGS resonator, for multi-stopband filter on CPW, is presented, in the frequency range from 0-11 GHz. First, the complete structure of the resonator and where the reconfigurability elements are put are explained. The structure has three different switches on each side of the CPW ground planes, giving four different configurations. As a first design step, these switches are modeled as ideal ones, i.e. open and short circuits. In each configuration, the structure has been modeled using the parallel RLC circuit, fabricated and measured, where all results show good agreement. The resonator is then implemented using PIN diodes as the reconfigurability element. The measurement results with the measurement setup are illustrated in the thesis. Finally, the last step of this study is to use the DGS in the implementation of the bandpass filters. Two applications of the DGSs are presented. First, a compact inductively coupled BPF using the DGS unit cell operating at 5 GHz is implemented. Then to validate this theory, another filter of the same type of order two at the same frequency is designed. Then, a reconfigurable bandpass filter using this structure is proposed. Using a MEMS switch, the structure would convert from a single resonance structure at 5 GHz to a multi resonance structure at 2.8 and 8 GHz. The second application is the enhancement of the ring resonator filter. Ring resonator based filters are featuring attractive behavior but they are suffering from two kinds of drawbacks that limit their implementation in real applications. The first one is their large size due to the two tuning stubs, while the second deals with the existence of higher order modes which limit the out-of-band rejection. Both issues degrade the whole system performance and need to be assessed to find solutions to overcome these drawbacks. This thesis aims to propose some solutions to reduce the size and increase the rejection of the stopband of the ring resonator filter, while keeping its overall performances with respect to its wide bandwidth, sharp rejection and low insertion-loss. In order to do so, two different design approaches are considered. The first is at the filter layout level, through a space saving redesign of the tuning stubs, while the second is at the wave propagation level, through the exploitation of DGS properties. Finally, for future work, the implementation of these structures on silicon substrates using MEMS switches and ferroelectric materials is proposed to achieve overall better performance and easy tuning.
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Submitted on : Wednesday, January 13, 2010 - 2:01:10 PM
Last modification on : Thursday, June 10, 2021 - 3:03:00 AM
Long-term archiving on: : Friday, June 18, 2010 - 12:48:08 AM

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  • HAL Id : tel-00446721, version 1

Citation

Heba Badr El-Din El-Shaarawi. Structures électromagnétiques à bandes interdites pour des applications de filtre. Micro and nanotechnologies/Microelectronics. Université Paul Sabatier - Toulouse III, 2009. English. ⟨tel-00446721⟩

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