Conception de circuits micro-ondes multi-bandes et a frequences agiles pour la realisation de systemes sans fil reconfigurables

The research work in this thesis concerned with the design and realization of radio frequency (RF) and microwave components, and a complete receiver system, with multiple functionality such as multi-bands and reconfigurable operation frequencies bands based on standard silicon or ferroelectric (BST -- barium strontium-titanate) varactors.;Thin-film BST-based and conventional silicon varactor-based tunable dual-band quadrature hybrid couplers are characterized and compared in this thesis. Both structures are composed of four quarter-wavelength sections at a frequency located between the two operating frequencies and with two pairs of open-ended stubs. Frequency tuning makes use of both BST interdigital and silicon varactor diode capacitors connected at the open-ended stubs. With two-tone non-linear characterization test, the BST tunable coupler biased at 0 and 25 volt presents an IIP3 of +25.45 and +35 dBm, respectively, while +11.5 and +34 dBm are obtained for the silicon varactor tunable coupler.;A dual-mode dual-bandpass filter for the U-NII bands is proposed and demonstrated. Its effective size reduction is achieved by using a multilayer configuration. The first and the third layers incorporate microstrip dual-mode bandpass filters with operating center-frequencies of f1 = 5.2 GHz and f2 = 5.8 GHz respectively. The second layer is used as a common ground plane for both filters, which also serves as a decoupling interface. Capacitive coupling transition is used to connect both filters to I/O coplanar waveguide (CPW) ports. Single and dual-band passband filter prototypes are designed, fabricated and measured in this work, thus validating the design principle.;A tunable dual-mode microstrip bandpass filter for mobile GSM and ISM bands (2 GHz to 2.45 GHz) is proposed and characterized. The structure is composed of a meander loop dual-mode resonator and four loading capacitances. Perturbation of the degenerate modes is achieved by the combination of a small square patch and an additional meander line resonator. Frequency tuning is made possible by modifying the electrical length of orthogonal quarter-wavelength meander arms with four varactor-diode capacitors.;In the first part of this thesis, a simple and fast measurement technique is developed to extract BST loss tangent and dielectric constant through an interdigital BST capacitor. Also, the electrical model obtained for the BST capacitor presents features of resistive loss variation and capacitance tunability.;A low-cost dual-band low-noise amplifier (LNA) is proposed and demonstrated for its use in WLAN IEEE802.11b/g/a standards. A sufficient dual-band gain is achieved on the basis of cascaded two single-stage amplifiers. The proposed LNA is realized in our standard Print Circuit Board (PCB) surface-mount technology with discrete components.;A frequency-agile dual-band direct conversion receiver is proposed and experimentally validated for cognitive radio system applications. Two types of tunable receiver architectures are presented and analyzed in this work; one structure relying on a tunable bandpass filter, and a second system based on a varactor --based tunable six-port demodulator, with the latter showing better sensitivity and dynamic range. In order to demodulate phase-shift-keying (PSK) modulated signals at multiple operating frequencies at a high bit rate of 40 Mbps, the receiver is designed using a wideband power detector in connection with a high-speed quad comparator. An experimental prototype and a complete measurement test bench have been realized in order to obtain bit error rate (BER) performances of the receiver in a more realistic application environment. (Abstract shortened by UMI.)...