Abstract:
This thesis presents an optimized, broadband, Doherty-based amplifier that employs an unequal power split between the main transistor and the six-auxiliary transistors. Different unequal power splits are adopted to optimize the output power and enhance the back-off power (BOP) level efficiency of the amplifier in comparison to an equal power splitting topology. The amplifier operates at a bandwidth of 2 GHz with a (BOP) of 8 dB, drain efficiency greater than 40%, and a fractional bandwidth of 100%. We tested the final optimized design at the LAB using a driver amplifier, signal generator, and spectrum analyzer. The input radio frequency (RF) signal is a continues-wave (CW) and its frequency swept from 1.8 to 3.8 GHz. The experimental measurements show a Doherty-like efficiency behavior from 1.8-3.8 GHz. The output power is 40±3 dBm and 43.8±2.3 dBm, corresponding to 8 dB BOP and peak power levels, respectively. The measured drain efficiency is between 45%-60%, and 42%-70% respectively. The efficiency of the optimized amplifier at the BOP level is improved. Therefore, it can be used for many modern communication systems, especially for those who have a high peak to average power ration (PAPR). Also the load modulation effect of the conventional DPA is totally removed. Hence, the operating bandwidth of the amplifier is increased, which means that the amplifier can handle many signals at the same time. So a single power amplifier can be used at the base station instead of using multiple ones.
