FD-TD analysis of coaxial probes inserted into rectangular waveguides

Full-wave FD-TD analysis has been carried out for coaxial probes inserted i nto waveguides. Both single and symmetrically placed paired coaxial probe s tructures have been discussed and we have revealed the relation between equ ivalent circuit parameters and structural parameters of the coaxial probes including cases for large diameter and extension length, which is useful fo r practical waveguide circuit design. The equivalent circuit parameters cal culated from the scattering parameters agreed well with corresponding measu red data. From the calculated field in a waveguide, field concentration at sharp edges of probe sole or base, which ought to be taken into account for high power application design has been also discussed. Besides, amplitudes of higher order modes in waveguides excited by coaxial probes or pairs of coaxial probes has been calculated so as to estimate the range beyond which higher order modes decay sufficiently. This estimation is necessary for si mple and easy design of probe using circuit theory.