Research of the cutoff characteristic of the dominant mode in ridge-trough waveguides

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.