الفهرس 
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Abstract
As the world is moving towards reduced transmission power dissipation and reduced radiation, new design of power amplifiers are necessary. This is because that power amplifiers are the bottleneck in the transmission path. Around 50-80% of transmitter power is consumed in Radio Frequency Power Amplifiers (RFPA). The aim of Green Communications is to decrease the power dissipated or consumed in communication systems while maintaining high quality of communication capacity. Recently, the researchers has been discovered Class E and Class F as switched mode PA for the sake of high efficiency but on the expenses of linearity degradation. On the other hand, the High Electron Mobility Transistor (HEMT) fabricated from GaN is found to be the best candidate for efficient high power handling capability. Therefore, RFPA design using GaN transistors is adopted in this research to maintain high efficiency, high output power as well as high linearity, to give us the green communication environment.
An early study fabricating AlGaN/GaN Hetero-junction Bipolar Transistors (HBT) is modeled. The potentials and limitations of the model are analyzed using common Figure of Merit (FOM) definitions. Comparison between GaN and GaAs based HBT is obtained. Based on this study, it is found that GaN HBT would be helpful in terms of minimum dissipation and maximum power handling capabilities. But, it still faces too many fabrication problems as explained in this thesis which degrades its maturity to leave the research phase towards production phase. Therefore, it is understood that why researchers are taking the direction of GaN HEMT instead of GaN HBT.
This thesis introduces nonlinear model parameter extraction for GaN HEMT transistor that can be utilized in the design of power amplifiers for green communications. The GaN HEMT transistor achieves very high power densities and breakdown fields. A power amplifier based on GaN HEMT TGF 2023-01die transistor is designed and tested on a WiMAX standard from 3.2 to 3.8 GHz. The results of the experiments are compared with the conventional GaAs in the same application. Criteria such as: transmission mask, output power, power gain, 1dB compression point, drain efficiency and adjacent channel power ratio are used in the comparison. Both circuits are designed, validated and verified using ADS simulation tool. In this Thesis, it has been proved that the proposed RFPA compliances with green communication requirements. The results show that efficiency is actually doubled while the maximum output power is enhanced by 7dB. In addition, the adjacent channel power ratio is increased by (15-20) dBc which makes the transmission mask deeply complies with the WiMax standard.
But, the fabrication of this RFPA faced assembly problem due to the need of wire bonding of the Die transistor. Therefore, the final PA stage is redesigned using Cree CGH40010 GaN packaged transistor including its biasing network as class A PA and stabilization networks. Dual tone Harmonic Balance simulation is used with EM-Circuit-Co-Simulation. This proposed PA achieves efficiency tends to 48%, with output power of 38dBm at 1-dB compression point and power gain of 13 dB. It satisfies the linearity requirements with 3rd order intermodulation distortion of -24 dBc and harmonic distortion better than 45dBc. This PA is fabricated on Teflon substrate using microstrip photolithographic technology. Measurements agrees well with simulations which verifies the proposed idea as well as the design methodology.
Keywords: Green communications, GaN HEMT, nonlinear transistor model, high efficiency, RF power amplifier.