<div>Radio Frequency Power Amplifiers (PA) are essential components of wireless systems and nonlinear in a permanent way. So, high efficiency and linearity at a time are imperative for power amplifiers. However, it is hard to obtain because high efficiency Power Amplifiers are nonlinear and linear Power Amplifiers have poor efficiency. To meet both linearity and efficiency, the linearization techniques such as Digital Predistortion (DPD) has arrested the most attention in industrial and academic sectors due to provide a compromising data between efficiency and linearity. This thesis proposed on digital predistortion techniques to control nonlinear distortion in radio frequency transmitters. </div><div>By using predistortion technique, both linearity and efficiency can obtain. In this thesis a new generic Saleh model for use in memoryless nonlinear power amplifier (PA) behavioral modelling is used. The results are obtained by simulations through MATLAB and experiments. We explore the baseband 13.56 MHz Power Amplifier input and output relationships and reveal that they apparent differently when the Power Amplifier shows long-term, short-term or memory less effects. We derive a SIMULINK based static DPD design depend on a memory polynomial. A polynomial improves both the non-linearity and memory effects in the Power Amplifier. As PA characteristics differs from time to time and operating conditions, we developed a model to calculate the effectiveness of DPD. We extended our static DPD design model into an adaptive DPD test bench using Indirect Learning Architecture (ILA) to implement adaptive DPD which composed of DPD subsystem and DPD coefficient calculation. By this technique, the output of PA achieves linear, amplitude and phase distortions are eliminated, and spectral regrowth is prevented. </div><div>The advanced linearity performance executed through the strategies and methods evolved on this thesis can allow a higher usage of the capability overall performance of existing and emerging exceptionally performance PAs, and therefore an anticipated to have an effect in future wireless communication systems. </div>

La technologie Ultra WideBand (UWB) sur fibre est une solution prometteuse pour répondre aux enjeux des futurs réseaux de communication WLAN/WPAN. Les caractéristiques de la fibre, incluant son énorme bande passante, offrent la possibilité d'une bonne qualité de service à longue portée. La propagation sans-fil UWB doit être réalisée sous des contraintes de densité spectrale de puissance particulières, imposées par l'autorité de régulation (FCC pour les Etats-Unis). La nouveauté de notre travail provient de I' exploitation des avantages d'un amplificateur optique à semi-conducteurs (SOA) afin d'obtenir une extension de portée à un coût et une complexité limités. Cependant, les effets non linéaires et le bruit d'émission spontanée amplifiée (ASE), intrinsèques à ce type de composant, sont susceptibles de dégrader la performance du système. La réduction de ces effets indésirables a donc été d'une importance centrale dans cette étude. Les non-linéarités du SOA ont été compensées en appliquant une solution de pré-distorsion analogique des formes d'ondes électriques. Un traitement basé sur phaser a également été proposé pour réduire simultanément I' influence de I'ASE et linéariser les caractéristiques du SOA, grâce à des opérations de chirping réparties entre l'émetteur et le récepteur. Avec la transmission Impulse Radio, en raison des propriétés temporelles des formats de modulation, des raies spectrales apparaissent, ce qui peut violer la limite FCC ou réduire I' efficacité énergétique. Une nouvelle technique de randomisation de formes d'ondes a été étudiée, qui s'est révélée efficace pour supprimer ces pics spectraux. Les trois approches ont montré un grand potentiel avec les formats On Off Keying et Pulse Position Modulation, à longue portée optique. Les performances d'une modulation différentielle Chaos Shift Keying ont finalement été examinées; une probabilité d'erreur inférieure a été obtenue expérimentalement en comparaison avec d'autres modulations non cohérentes. / Ultra WideBand (UWB) over fiber is a promising technology for meeting the demands of future wireless local-area networks (WLANs) and wireless personal-area networks (WPANs). Thanks to the enormous bandwidth and fiber characteristics, a high communication quality may be established at long reach. UWB wireless propagation must be achieved with special power and spectral constraints fixed by the regulatory bodies (e.g. US Federal Communication Commission). The novelty of our work originates from exploiting the benefits of a Semiconductor Optical Amplifier (SOA) so as to get a reach extension at limited cost and complexity. However, the inherent nonlinear effects and Amplified Spontaneous Emission (ASE) noise associated to such device may affect the system performance.Overcoming these impairments has been of central importance in this study. SOA nonlinearities have been mitigated by applying analog pre-distortion in electrical domain. Phaser-based processing was also proposed to simultaneously reduce ASE influence and linearize SOA characteristics, thanks to up/down chirping performed on the transmitter/receiver sides. With Impulse Radio UWB transmission, due to the time properties of modulation patterns, discrete lines arise in the corresponding spectrum, which may violate FCC limit or reduce the power efficiency. A new shape randomization technique has been investigated, which proved to be effective in suppressing these spectral spikes. The three approaches have shown a great potential with On Off Keying and Pulse Position Modulation formats at long optical reach.The performance of Differential Chaos Shift Keying was finally examined in the over fiber system, a lower error probability was experimentally achieved in comparison with other non-coherent modulations.

This doctoral thesis is focused on problems of modulators based on six-ports. It begins with description of current state of the art of six-ports used like modulators, their transfer functions and SIW technology. A design part of this thesis consists from experimental six-port based on substrate integrated waveguide (SIW) technology. There is presented step-by-step development of this six-port using this technology and also there is introduced micro-strip technology based six-port. Final design of six-ports and variable impedances were measured, the results are discussed and compared with expected ones in next chapters. Second part of this thesis deals with influences of internal parameters of six-ports to final signal transmission and derives theirs transfer functions for more than one reflection in structure. The computation results are compared with experimental measurements for fixed loads. With using of ideal loads sweeps, modulations with shaped input signals were calculated. For designed variables impedances, there was founded the optimal biasing points for demanded IQ diagram and discussed which from tested active circuit is suitable. In the last part there are shown results of experiment with these variable loads connected to both types of designed six-ports.