Research On Nonlinear Correction Technology Of Microwave Power Amplifier

Linearity is one of the most important indicators for measuring the performance of microwave communication systems.The microwave power amplifier(PA)is the most important part of the communication system,of which linearity directly affects the performance of the whole system.When the input power of the microwave power amplifier reaches a certain level,it will generate serious nonlinear distortion,which will not only affect the information quality of the transmition channel,but also have a significant impact on adjacent channels.Therefore,it is imperative to improve the linearity of the communication system.This paper makes a detailed analysis of the nonlinear characteristics for the 5G frequency band PAs.The advantages and disadvantages of several nonlinear correction techniques are compared.Due to the fact that the analog predistortion(APD)circuit is simple in structure,relatively cheap in cost and wide in bandwidth,so it is very suitable for the nonlinear correction research of the microwave PA.This paper designs a microwave PA and three new APD circuits at 3.5GHz frequency,of which two new APD circuits are designed for the avago technologies' ALM-31322 microwave PA.One is an APD circuit,which is designed with the open short microstrip line to compensate the phase,which can adjust the phase difference between the fundamental signal and the third order inter-modulation distortion.The test results show that dual-tone signal of the ALM-31322 PA reduces 0.9dB and IMD3 reduces about 34 dBc.The other is a new analog predistortion circuit that uses a DC power supply to control the quiescent point of three schottky diodes.This structure increases the nonlinearity of the APD with reducing the circuit complexity.The test results show that the output dual-tone signal of the ALM-31322 PA reduces 1dB and IMD3 reduces about 31 dBc.Moreover,a new dual-branch analog pre-distortion structure is also designed for the 3.5GHz Class-E PA.The simulation results show that IMD3 under the dual-tone signal reduces about 22 dBc and IMD3 under the four-tone signal reduces about 8dBc when the fundamental output is the same.This paper also studies the nonlinearity of PAs at 28 GHz,which is designed with the HMC1132 chip.Two new APD circuits are designed by software simulation.One of the two APD circuits is a new single-branch push-pull APD circuit,which adds the push-pull structure and the AC/DC separate grounding structure to the traditional structure.The simulation results show that the gain amplitude expansion is 1.2dB-6dB and the phase expansion is 8°-80° when the DC bias voltage is 0.6,0.8,1,1.2,1.4 and the input signal power is from-15 dBm to 3dBm.The other APD is a new Ka-band balanced dual-branch APD circuit,which implements the balance of the upper branch and the lower branch on the basis of four 3dB couplers.The push-pull structure and the AC/DC separate grounding structure are also implemented in the internal circuit.The simulation results show that the gain amplitude expansion is 2dB-9dB and phase expansion is 30°-90° when the DC positive power supply of the nonlinear circuit is added with voltages of 0.7V,1V,1.3V,1.6Vand 1.9V,the other power supply voltage values are fixed and the input signal power is from-15 dBm to 5dBm.