A dyadic Green's function for the plano-concave quasi-optical resonator

An approximate dyadic Green's function is derived for a quasi-optical resonator. The Green's function is comprised of resonant and nonresonant terms corresponding to coupling of the modal and nonmodal resonator fields. The effect of losses due to diffraction, finite reflector conductivity and radiation are included. Experimental one- and two-port measurements of antennas in an X-band cavity compare favorably with theoretical predictions.>