The criterion for the coupling states between cavities with losses

For a coupled two cavity system it is important to know whether the two cavities are coupled, critically coupled or under coupled with given coupling coefficient k and quality factor Q0. A quantitative criterion is given to make the judgement. It is found that kQ0>2, kQ0=2 and kQ0<2 correspond to the three cases stated above. The analytical formulae for the phase shifts resonant frequencies and field ratio in a coupled two cavity system are given as a function of cavity quality factor Q0 and coupling coefficient k. The detailed discussion about a coupled two cavity system has been easily extended to a multi cavity standing wave structure. (K.A.). 2 refs., 4 figs