This paper presents an analysis of a multi-hole directional coupler attached to an overmoded circular waveguide. The directional coupler is analized as a boundary value problem, and is solved numerically by a virtual cavity method. The approximate analysis of a small hole coupling coefficient is verified by this analysis. Numerical results indicate that the mutual coupling between holes is not negligible for calculating the directivity of the directional coupler.

This letter presents an approximate analysis for coupling coefficients of a multi-slotted directional coupler to diagnose propagating modes in an output waveguide of a gyrotron. The coupling coefficients are calculated approximately and verified by a rigorous analysis.