为了研究脊槽波导主模截止特性，采用亥姆霍兹方程的有限差分格式，计算在窄边与宽边比为0．45、槽的高度与窄边比为0．4的条件下，脊槽波导中脊和槽的几何尺寸在中间位置连续变化时的归一化截止波长。并且计算了当脊宽为0、脊槽间距为窄边长度加槽高度，即脊槽波导的脊消失，成为单槽波导的归一化截止波长。并将计算结果与单槽波导和单脊波导的进行对比。结果表明，脊槽波导的截止特性较单脊波导和单槽波导更加良好。

Based on the finite-difference format of Helmholz equation,the normal cutoff wavelength of the dominant mode in the ridge-trough rectangle waveguide is calculated under the condition that physical dimensions of the ridge and the trough vary continuously in the middle of the waveguide while the ratio of short side to long side is 0.45 and ration of the height of the trough to the short side is 0.4.Then the normal cutoff wavelength of the single-ridge waveguide is calculated,which is considered as the ridge of the ridge-trough rectangle waveguide disappear for the width of the ridge equals to 0,the space length equals to the short side plus the height of the trough. A conclusion is made that the cutoff characteristic of the ridge-trough waveguide is better than that of a single ridge waveguide or a single-trough wavegide.