The static scattering properties and phase behavior of mixtures of homopolymers and diblock copolymers are considered. The effects of architecture on these properties are investigated. In particular, the results obtained for mixtures with cyclic homopolymers and copolymers are compared with those obtained in the case of mixtures of Linear chains. Depending on the concentration of copolymer, one may observe an interplay between macrophase and microphase separation transitions. This interplay is investigated for cyclic and Linear chain systems. Mixtures made of cyclic copolymers show enhancement of compatibility towards phase separation. Phase diagrams are plotted to show the compatibilization. Effects of topological constraints on chain architecture and interactions are ignored for cyclic chain systems.