Abstract
In this paper, we get the windows by simulation with calculation. We used the Maxwell’s equation to get the eigenmodes. And modal analysis is applied to calculate the amplitudes of those excited waveguide modes in radius discontinuity problem. We will get the amplitude of other modes by orthogonalities of waveguide eigenmodes. We extend the result to multi-discontinuity case by use linear algebra technique. We used to analyze windows and periodic structure. And compare the results of the calculation to the concept of impedance matching of mode effect are not considered, and investigates the result of different situations. On the results, we take periodic structure, so we are cyclical changes with frequency. We can get some pass bands in high frequency.