Transient analysis of circular waveguide probe excitation using Cavity Modal Expansion

Circular waveguide TM_0n excitation in time-domain with axial current probe is analyzed using Cavity Modal Expansion (CME). It is based on expanding the electromagnetic fields inside a fictitious waveguide cavity, a section of the waveguide containing the exciting probe, in terms of solenoidal and irrotational modes. Using these field expansions in Maxwell´s equations renders a system of time-domain ordinary differential equations of the cavity mode amplitudes, giving when solved the transient behaviour. The propagation through waveguide port is obtained through projecting the cavity modes on the waveguide ones at the interface port between the cavity and the guide. Results obtained using the proposed method are compared with the analytical solution for sinusoidal excitation and transient results using CST Microwave Studio (MWS).