Explicit expressions for the self admittance and the mutual admittance Yij between two arbitrarily polarized circular apertures are presented. The aperture field distribution is that of TE11 circular waveguide mode. The analysis makes use of a spherical mode expansion and of the addition theorem for tesseral harmonics. Numerical results show Yij as a function of angular separation θ. The E-plane coupling exhibits asymptotic (large θ) behavior consistent with the lowest “hard” surface ray order results. The slope of the H-plane coupling for large values of θ does not correspond to the lowest-order “soft” surface ray attenuation, but rather to that of the lowest-order “hard” ray. This behavior is explained.