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.