Time-dependent dyadic Green´s functions for rectangular and circular waveguides

Closed-form expressions for the time-dependent dyadic Green´s functions of electric and magnetic types for rectangular and circular waveguides are derived from the dyadic Maxwell equations in the time domain. These functions can be used to obtain the time-dependent electric and magnetic fields propagating in those guides due to any arbitrary time-dependent current distribution inside the guide. Stationary vector wave functions are introduced that separate the space-dependent parts from the time-dependent parts of the Green´s functions. Comparison of the results for the rectangular and circular guides reveals that the time-dependent parts are identical. Thus the results can be easily extended to some other cylindrical pipes such as elliptical waveguides and also to coaxial cables