Wideband matching technology used for predistortion linearization
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摘要: 由于放大链路的增益波动以及不同频点之间非线性特性的差异，预失真器难以在不同的频点同时实现非线性特性匹配，即令整个频带内不同频点的线性度指标同时满足要求。由于预失真器和放大器之间的非线性失配，放大器在某些频点的非线性特性还会恶化。本文从线性化器与预失真器的宽带匹配出发，讨论了预失真线性化器与行波管放大器宽带匹配的条件以及非线性失配所带来的影响，当增益失配误差不大于1 dB时，在行波管放大器自身的三阶交调值不大于40 dB的非线性动态范围内，三阶交调下降幅度最大值为4.1 dB；通过采用级联增益补偿电路的方式，降低链路增益波动，实现预失真器和放大器的非线性匹配，真正拓展预失真线性化器的工作带宽。Abstract: Due to the gain fluctuation and nonlinear characteristic variation of the TWT amplifier chain, predistorter cannot compensate the nonlinearities at different frequencies within the working band, thus nonlinear mismatch might occur and nonlinearity of TWTA could get worse at some frequencies. The wideband linear match theory of predistorter with TWTA is put forward, and the influence of nonlinear mismatch is discussed. Predistorter cascaded with gain compensation unit can flatten the gain fluctuation and match the nonlinearity of TWTA, truly broaden the linear working band of LTWTA.
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图 2 三阶交调下降值与增益波动误差的关系
Figure 2. Relationship between third-order intermodulation degradation and gain error
图 4 预失真器和行波管放大器不能良好匹配时，LTWTA的AM/AM特性曲线
Figure 4. Curves of AM/AM characteristic of LTWTA when PD and TWTA is not well matched
图 6 预失真线性化器的幅频特性和相频特性
Figure 6. The amplitude-frequency and phase-frequency characteristics of PD
图 7 行波管放大器线性化前后的增益和相位特性
Figure 7. Gain and phase characteristics of TWTA and LTWTA at there frequencies
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