چكيده به لاتين
Newer telecommunication systems, such as WIMAX, LTE, or satellite systems, use variable envelope signals or efficient spectrum modulation methods. These networks require high-efficiency, low-distortion linear power amplifiers. The power amplifier is an important element in wireless telecommunication systems, and there is a serious challenge to designing a power amplifier with high gain, linearity, and proper efficiency. In a power amplifier, there is usually an inverse relationship between linearity and efficiency, and on the other hand, the components used in the power amplifier show nonlinear effects in large signal amplitudes, and this causes distortions within the band and Outside the information signal band, In-band distortion increases the bit error rate and out-band distortion causes the output spectrum to expand, which interferes with adjacent channels. Therefore, to have high efficiency at the same time as linearity, we must apply linearization to high-efficiency amplifiers. In this thesis, we study the second harmonic injection method and its effect on the ductility of the two-power amplifier in the frequency band of 3.55-3.7 GHz, and because the Doherty power amplifier includes two main and auxiliary amplifiers, we also study the second harmonic injection to each of the main and auxiliary amplifiers and its effect on the linearity of the whole structure of the Doherty power amplifier. At first, we designed a structure with four injection paths to the input and output of the Main and auxiliary amplifiers. By injecting the second harmonic signal separately, we compared them with each other in terms of improving the linearity. Then, due to the main amplifier playing an essential role in the nonlinearity of the Doherty structure, at this time, designed two Doherty power amplifiers (by injecting the second harmonic signal to the input and output of the main power amplifier separately), and compared the improvement rate of them in the linearity of the whole structure. Finally, since this method is more effective in improving the linearity of the entire Doherty structure when injected from the input of the main amplifier, we analyzed this final structure by using full-wave analysis in the momentum environment of ADS software. We extract the layout of all designed networks up to the fifth harmonic. The designed DPA has an output power of 52-62 watts with a drain efficiency higher than 73% in its saturation. It also provides a drain efficiency of better than 57% at 6dB-output back-off (OBO). By applying a second harmonic signal to the output and input of the main amplifier in single-tone analysis, the gain of the DPA structure becomes flatter. In two-tone analysis, the SHI from the PA's input and output results in an improvement of better than 55 dB and 30 dB in the third-order intermodulation (IMD3), respectively. Therefore, to show the nonlinearity of a power amplifier, we will use various parameters such as AM-AM, AM-PM, and IMD3, which are criteria for expressing the nonlinearity of a power amplifier.
