Design Of Analog Predistortion System In VHF Band

With the rapid development of the world, the wireless communication business has been universal. Power amplify is one of the important components. The performance of the amplifier will affect the performance of the entire system. When the output power of the power amplifier is high to a certain extent, a significant nonlinear distortion will appear. Nonlinear distortion limits the performance of the power amplifier, thus affecting the performance of the whole system. So improving the nonlinear distortion is important for the performance of the power amplifier and the whole system.The causes of the nonlinear characteristics of the power amplifier was analyzed. The indicators used to represent the nonlinear of power amplifier was introduced. Several common linearization techniques was studied and compared. The overall technical indicators of the analog predistorter was Proposed. At the same time a detailed plan comparison was carried out. An analog predistorter of two loop structure was adopted, which can get predistortion signal by the first loop, and the second loop was used to regulate the phase and amplitude of the predistortion signal. Based on bicyclic analog predistortion architecture, an analog predistorter which work in the band 279.3MHz to 289.5MHz was designed. The key components were designed and simulated.Based on the up design, an analog predistorter was maked, and each device was tested. Test results show that the performance of each device can achieve the desired requirements. Meanwhile, aimed at the VHF band power amplifier, the single-loop testing, the bicyclic testing, and the cascade test between the analog predistorter and the power amplifier were done. The results show that the nonlinear index of the power amplifier has been significantly improved, and three order intermodulation(IMD3) get 10 dB improvement.