中文摘要：

波导不连续性分析在波导谐振腔和滤波器的准确设计等方面具有重要意义。首先引入了同轴终止于圆波导的不连续性的等效网络,然后应用Rayleigh-Ritz变分法确定了等效网络中的等效电容的上下限值,等效电容的变分数值结果和HFSS仿真结果及文献中所给结果吻合得很好。结果表明若取变分法计算所得的上下限值的代数平均值作为等效电容值,则该值在从低频到不连续性结构的最低次消逝模（Evanescent Mode）的截止频率附近的绝大部分频率范围内同HFSS的有限元分析结果间的误差≤1%。

英文摘要：

Analysis of discontinuity in waveguide plays an extremely crucial role in the design of resonators and filters. Equivalent network of a coaxial line terminated in a circular waveguide is introduced first, and then Ray- leigh-Ritz Variational Method is adopted to obtain the upper and lower bounds of the discontinuity capacitance. Nu- merical results of Rayleigh-Ritz Variational Method agree very well with simulation results of HFSS and results in the reference. The example of the variational computation shows that if arithmetical mean of the upper and lower bounds of the capacitance is taken as the value of ＇the equivalent capacitance, then of majority frequencies raging from low frequency to near cutoff for the lowest evanescent mode of the structure, the percentage errors between the values of discontinuity capacitance computed from variational technique and HFSS simulation ones gained by FEM, are lower than 1%.