The Design Of RF Power Amplifier

RF power amplifier is always used at the end of the Radar system and any otherkind of radio transmitters to improve the magnitude of the output RF signal. The powerconsumption and bit error rate of the system are two important parameters to weight awireless communication system’s performance. RF power amplifier is the mainlynonlinear and dissipative device, so the method of increasing the efficiency and linearityof RF power amplifier would be the key aspects in RF power amplifier research.The basic theories for designing RF power amplifier and specifications of poweramplifier are introduced in Chapter2and Chapter3. The basic principle to improve theefficiency of symmetrical Doherty power amplifier and multistage Doherty poweramplifier is introduced in Chapter4. In Chapter5, the output impedance of poweramplifier is obtained at large signal state via load-pull technique. Microstrip lines areused to design the input and the output matching network. Finally, A Class AB poweramplifier with2.4GHz center frequency and200MHz operation bandwidth wasdesigned and optimized. An experimental RF power amplifier is fabricated on thepolytetrafluoroethene substrate with2.65relative permittivity and1mm thicknessthrough traditional PCB process. The measured results show that the power gain isgreater than30dB, the return loss is less than-10dB between2.3GHz and2.5GHz, theoutput power is greater than6Watt. The power added efficiency of final stage poweramplifier is up to30%.Based on the Class AB power amplifier, a symmetrical Doherty power amplifierwith2.4GHz center frequency was designed at the same time. According to designdifficulty of Doherty power amplifier, the power combiner circuit of Doherty poweramplifier is the key point during designing procedure. Meanwhile, the offset line’sfunction of main amplifier and auxiliary amplifier at the power combiner circuit wasalso discussed. From the simulation results, the power added efficiency of Dohertypower amplifier is about nearly10%higher than that of Class AB power amplifier’s.Finally, an experimental Doherty power amplifier circuit was fabricated. The measuredresults show that the power gain for main power amplifier of Doherty power amplifieris12.69dB and the return loss is-10.395dB at2.4GHz; For the auxiliary amplifier ofDoherty power amplifier, the power gain is9.39dB and the return loss is-7.16dB at2.4GHz. The main work in this paper has been summarized and the further research work ispresented.