基于正态分布宽带信号的无源互调特征行为分析

Characteristic behavior analysis of passive intermodulation based on normal distribution wideband signal

摘要:

在现代无线通信中，无源互调是影响通信信号传输质量的重要因素。双音互调测试能够有效衡量无源器件的非线性特性，却无法准确预测出器件在宽带信号激励下的非线性失真。因此本文提出了一种基于正态分布的宽带信号激励下的射频连接器无源互调特性分析方法。通过双音互调测试，建立射频连接器无源非线性传输数学模型，并将基于正态分布的等效宽带信号作为非线性传输模型的激励源进行模拟仿真。结果表明，宽带无源互调功率分布与宽带信号功率分布相同，n阶宽带无源互调带宽为原宽带信号带宽的n倍，宽带信号的无源互调产物相较于双音测试信号有所增强，且信号的信噪比下降，说明宽带信号在传输过程中受到的干扰更加严重。电路仿真和数值计算呈现出良好的一致性，证明了本分析方法的有效性。

Abstract:

In modern wireless communication, passive intermodulation is an important factor affecting the transmission quality of communication signals. Dual-tone intermodulation testing can effectively measure the nonlinear characteristics of passive devices, but it is hard to accurately predict the nonlinear distortion of devices excited by broadband signals. A method for analyzing the Passive Intermodulation characteristics of RF connectors with broadband signal excitation is proposed. Through the dual-tone intermodulation test, the passive nonlinear transmission mathematical models of RF connectors are derived. An equivalent broadband signal considering normal distribution is provided as the excitation source to the connectors. Mathematical calculation results of the proposed model show that the broadband Passive Intermodulation power distribution is the same as the broadband signal power distribution. The bandwidth of the nth-order broadband Passive Intermodulation is n times that of the original broadband signal. It is observed that the power of Passive Intermodulation products with broadband signal excitation are higher than that of the dual-tone signal. Thus, the signal to noise ratio decreases, indicating that the PIM interference induced by the broadband signal in the transmission process is more serious compared with that induced by two Continue Wave(CW) signals. Simulations are conducted by importing the proposed broadband signal and nonlinear transfer function to an equivalent circuit. The simulation results show good consistency to the theoretical calculation, which proves the effectiveness of this analysis method.