Design And Research Of Radio Frequency Power Amplifier

RF power amplifier is a key component of various RF systems and has been widely used in various fields of people's life.With the development of RF transistor technology and RF amplifier design technology,the design of power amplifier becomes more and more complex,and the requirements for its performance are also higher and higher.For example,in the communication system,it is required to meet the requirements of high linearity,high output power and high efficiency.This thesis follows the design steps of the linear rf power amplifier,aims at low cost and high performance,researches the linear RF power amplifier design with Keysight ADS in three directions: gain enhancement,power enhancement and efficiency enhancement,and some PCB boards has fabricated.The specific research work mainly includes the following parts:(1)The design method of class AB linear RF power amplifier is researched.The design targets are 800MHz~1GHz working frequency with 10 W output power and 30 dB gain,etc.,and gain enhancement is realized through two-level cascade structure.The main amplifier is designed with the classical LDMOS power transistor,to get maximal power,the impedancepull method is used to design matching network.To get maximal gain,the bidirectional conjugate matching method is used to design the matching network of drive amplifier.The bias and matching circuits are optimized,the harmonic balance simulation is used for nonlinear analysis,and the pcb layout is drawn.In addition,a bias power supply circuit with temperature compensation is designed.(2)Measuring power amplifiers which designed in the previous chapter,including static working point check,oscillation check,S parameter and power measurement.Single-stage and cascade measurement are carried out for these fabricated amplifiers respectively,although there is some gap between the actual measurement and simulation,but after matching adjustment,the target is basically satisfied.Then the experience in design is summarized.(3)On the basis of the designed AB amplifier,the design of the balanced structure based on the coupled bridge is researched and the physical fabrication is carried out.The Simulation and measurement results show that although the volume of the balanced structure increases,it can realize power synthesis,improve the return loss in a wide band and improve the linearity.Through simulation finds that the imbalance of the two drain currents will reduce the gain and power and worsen the return loss.Then the simulation of classical Doherty amplifier is researched.Although the gain of Doherty structure is reduced,it can improve the power additional efficiency of power fallback to some extent.But it requires high quality substrate and can not work in wide frequency band.