Coupling efficiency of the rectangular waveguide resonators are discussed i
n terms of the method of angular spectrum theory. Under the condition given
in the paper, the coupling coefficients for the EH11 mode in the rectangul
ar waveguide resonator are presented as a function of mirror curvature and
position. It is shown that there exist two special geometries to provide lo
w coupling efficiency. The method can be applied to the other modes. (C) 20
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