电热耦合引起的微带传输线无源互调计算与验证

Calculation and Verification of Passive Intermodulation Caused by Electrothermal Coupling on Microstrip Transmission Line

为了克服传统微带点源模型中计算变量单一、缺乏物理机理分析的缺陷,提出了一种基于电热耦合效应的微带非线性传输线模型。首先在传统的传输线方程中引入3阶非线性电阻系数,确立了微带线中3阶无源互调(PIM)功率的计算方法;然后考虑电热耦合效应,给出了非线性电阻系数的数学关系式,结合电流密度的变化,得出了PIM功率随微带线宽度和频率的计算结果;最后通过实验对计算结果进行了验证,实验结果与理论计算比较吻合。计算与实验结果表明,相比于传统的非线性点源模型,结合电热耦合效应的非线性传输线模型对互调的计算分析更加完善,在微带线长度之外给出了微带线宽度、频率、输入功率等变量与微带线PIM功率的相对关系,能够更全面地预测微带线上无源互调的影响。

A nonlinear transmission line model of microstrip based on electrothermal coupling effect is proposed to overcome the defects such as single variable and lack of physical mechanism analysis in traditional point source model of microstrip.First,a 3 rd order nonlinear resistance parameter is introduced into the traditional transmission line model,and a method to calculate third order passive intermodulation(PIM)power is established.Then,electrothermal coupling effect is considered to explain nonlinear origin in microstrip and a mathematical expression of the nonlinear resistance parameter is given.The relationship of PIM power with line width and frequency is revealed through combining the change of current density Finally,experiments are implemented and experimental results agree well with the theoretical calculation The rationality of the theory is verified.Calculation and experimental results show that compared with the traditional nonlinear point source model the nonlinear transmission line model combined with electrothermal coupling effect is more perfect to the calculation and analysis of intermodulation.The new model reveals the relationship between PIM power and more parameters such as microstrip line width,frequency,input power,etc of the microstrip line in addition to the length of the microstrip line.The new model is more comprehensive in applications of PIM analysis andprediction.