Analytic expression of the aperture averaging function for Cassegrain system

Aperture averaging effect can smooth the optical signal fluctuations. Generally, the aperture function is assumed to be a single circle when its aperture averaging function K
₀
is calculated. In recent years, K
₀
function of a complex receiving aperture is also discussed. Actually, Cassegrain system is usually used as a telescope for free-space optical communication. There is a little bit difference from the previous analysis when Cassegrain system is used to analyze aperture averaging effect. K
₀
function of Cassegrain system is analyzed in this paper. The calculation result can be used to establish simulation model for optical propagation system.