Microwave Power Amplifier

Solid-state power amplifiers have advantages such as low DC supply, small size, high efficiency, high reliability and so on. They have been widely used in mobile communication, radar, jamming and identifying systems and possess an important status.In order to improve the utilize efficiency of the frequency resource, modulation manners such as QPSK and 16QAM are linear In the third-generation mobile communication systems. With multi-carrier and multi-channel, the RF systems distort if they are nonlinear. The distortion(inter-modulation distortion) results in errors in the magnitude and the phase of the modulated vector signal, enlarging the spectrum, disturbing the adjacent-channel, worsening the error-code-rate and so on. Power amplifiers are the main nonlinear devices in RF systems, so it's very important to improve the linearity of them. In our country, most of the linear-power amplifiers used in the wireless communication basestations are imported, and we must research and product them in our own country as soon as possible.Considering the demands of power amplifiers such as high-gain, high-power and high-linearity, This thesis has researched the microwave power amplifiers and linearity techniques and it is made of three parts:1. A S-band microwave power amplifier with 20W output power has been developed, and some methods for designing power amplifiers are analysed. Through theoretical analysis and simulation in the computer, a S-band microwave LDMOS FET power amplifier has been designed. The amplifier has four stages with some main charactersics as below: the work frequency band is 2110MHz～2170MHz, the power gain is more than 56dB, the gain flatness is±0.38dB, the VSWR is less than 1.3, and the IM3 is less than -40dBc when the output power is 20W.2. The thesis also studys linearity techniques used in microwave power amplifiers, placing emphasis on the feedforward technique and predistortion techniques. A simple structured analog predistorter with center frequency in 2.14GHz has been designed, containing a nonlinear generator, a divider, a power combiner, couplers and a vector modulator. The experiment shows that the predistorter is able to improve the IM3 of the first stage of the power amplifier developed in this thesis 20dB. It proves the foundation of the theories and a reference value for getting a better IMD.3. In addition, an adaptive control circuit is researched and its principle is introducted. Some main devices of the control circuit such as a Volt-Control Phase-Shifter and a Phase-Locked-Loop frequency synthesizer are designed and experimented, achieveing some staggered outcome.