| With the development of modern satellite data transmission communication technologies,satellites are carrying more and more functions.As more and more information need to be transmitted between satellites and ground,higher requirements on the system's communication rate and spectrum utilization rate are put forward.Therefore,the communication frequeny of modern satellite communication systems has gradually evolved from conventional S-band to X-band.And the modulation method has gradually evolved from constant-envelope modulation to non-constant envelope modulation.The use of non-constant envelope modulation technology can significantly improve spectrum utilization rate,but the modulation signal has a high peak-to-average ratio.If a conventional class AB power amplifier is used for amplification,in order to ensure the quality of the amplified signal,the amplifier has to work in a power retreat state.And the efficiency of the power amplifier will be greatly reduced,which increases the heat radiation burden and design cost of the satellite communication system.In order to improve the efficiency of the power amplifier power back-off region,this paper studies the X-band Doherty power amplifier and its applications in digital transmission field.Firstly,this paper introduces the current development status of satellite data transmission communication system.According to analyzing the problems existing in the systems using non-constant envelope modulation,the importance of the research on X-band Doherty power amplifiers is explained,and a more detailed introduction about the development of the Doherty efficiency enhancement technology is conducted.Then the theoretical basis of the power amplifier,the optimal power matching technology,the structure and principle of the traditional Doherty power amplifier are introduced.And the efficiencies of the different operating states of the Doherty power amplifier are deduced.Aiming at the deficiencies in the design of traditional Doherty power amplifiers,the improved schemes such as asymmetric design and full power matching design are introduced.Based on the related design indicators of the power amplifier system,the design scheme of the Doherty power amplifier system is given.In the selection of components,the requirements of high frequency and high withstand voltage are fully con-sidered.ADS(Advanced Design System)electromagnetic simulation software developed by Keysight is used to simulate the single-tube power amplifier and Doherty power amplifier.The load-pull simulation design method of single-tube power amplifier and the simulation design method of full-power matching Doherty power amplifier are given,and the circuit layout and cavity structure are completed.Finally,the power amplifier small-signal and large-signal performance test schemes are introduced.The performances of the driver amplifier,single-tube power amplifier and Doherty power amplifier circuits are tested based on the relevant test scheme.When the work frequency of the amplifer is 8.2GHz,the test results show that the efficiency of the Doherty power amplifier can reach 26.35% in the condition that the output signal has a 6d B back-off.Compared with the balanced power amplifier in the same condition,the efficiency of the Doherty power amplifier is increased by 11.54%. |
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