A novel approach for analyzing the quasi-optical offset Large Adaptive Reflector (LAR) Cassegrain system is described. In this system a Feed-Reflector is used to illuminate a reconformable hyperboloid subreflector with 5 similar to 10 in diameter, located 500 in above the ground. An exact equation for the offset LAR surface is given in this paper. To scan the beam up to 60degrees which is one of the LAR requirements, the concept of the dual offset LAR with the Feed-Reflector is introduced. In this design the cross polarization is eliminated by a proper orientation of the subreflector. The parameters of the configuration are obtained by utilizing generalized Gauss-Laguerre beam modes and matrix representation of beam mode transformation factor. In this design the blockage effect due to the Feed-Reflector is totally removed.