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The transient radiation from the open end of a circular waveguide is considered by simple analytical and direct numerical methods. The radiation of short pulse from the aperture is provided by calculation of special time form of field by means of modal basis method that permits to solve the problem of pulse evolution for positive and negative time with the use of Laplace transform. The radiation of the short pulse is calculated in Kirchhoff approximation and simulated by FDTD method. The frequency characteristics of the radiated field are considered.

transient radiation; circular waveguide; modal basis method