| The power amplifier (PA) is one of the key components of transmitting front-endsfor modern wireless communication systems, electronic countermeasure and radar, andso on. It plays a very important role in transmitter system. RF amplifier is the mainenergy-consuming module in communication system. The efficiency of RF poweramplifier not only affects the energy-consuming and stability of the wholecommunication systems, but also affects the usable time of the battery and dissipatingheat of device. The some high efficiency amplifiers, such as power amplifier usingnon-linear component, envelope tracking power amplifier and multistage Doherty poweramplifier, are adopted in foreign and domestic researches. However, these methodsincrease level of design complexity and device cost. The research to realize highefficiency power amplifier by simple circuits structures, has received more and moreattention from researchers.Usually, the amplifiers are nonlinear devices, especially in high efficiency poweramplifier. The linear technology has to be used for improving the non-linearity of poweramplifiers. Many traditional linearization techniques, such as predistortion andfeedforward, should be adopted. However, these methods require the use of externalcontrol circuits and signal processing, resulting in an increased circuits complexity andcost. Under eusuring high efficiency, the power amplifier with considerably high linearityhas become attractive difficult problem.At present, RF power amplifier is developing toward minimization and integration,however, it will affect the performance and the cost of communication systems. Besides,the structure is limited greatly in practical application. The miniaturization of poweramplifier with high performance is researched. The proposed power amplifier has wideapplied value in communication domain.The key technologies of RF power amplifier are researched in this thesis, and thereare some results have been acquired till now. The main contributions of this thesis aresummarized as follows: 1. To improve efficiency of Doherty power amplifier(DPA),the uneven DPA usingComposite Right/Left-Handed Transmission Line (CRLH-TL) is proposed base onspecial transmission performance of CRLH-TL. Due to flexible variety of power divisionratio and phase between main amplifier and auxiliary amplifier, the efficiency of poweramplifier is improved obviously. Furthermore, the sizes and costs are also reduced.2. In the improvement of DPA linearity research,the Doherty power amplifier usingcoupled line and a capacitive load is proposed. The conventional λg/4transmission line isreplaced by proposed structure to improve linearity. Due to suppression of the second andhigher order harmonics and modifying phase, the method can improve linearity of DPAobviously. Besides, the size of circuits is also reduced.3. In order to improve the linearity of Doherty amplifier, the structure with variablediode-load CRLH-TL is also proposed. Flexible tuning phase is achieved by the structure.Besides, the phase distortion of the peaking amplifier at a high power level can becorrected by tuning voltage of variable capacitance diode in CRLH-TL. So the linearityof Doherty amplifier is improved obviously.4. To improve accuracy of power in detected channel and reduce the size of poweramplifier, the high-directivity coupler using dual-layer printed Metamaterial NegativeRefractive Index/Microstrip (NRI/MS) is proposed, the proposed structure is of smallersize and wider bandwidth, furthermore, it also shows high directivity. Compared to theconventional coupler, the size of the proposed coupler is only60%of that in traditionalcoupler.5. Based on the performances of Stepped-Impedance Resonators (SIR) structure, adual-band power divider using SIR structure is proposed. The rejection level in stopbandis improved in the proposed structure. Furthermore, the size of devices and the costs ofRF amplifier modules are also reduced.
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