Structured design methodologies are needed in order to master the design and analysis of large and complex systems. Structured design methodologies for VLSI in general, are based on two main concepts, modularity and regularity. Modularity is used for decomposing a complex design into sub-parts that are more manageable, whereas regularity is aimed at maximizing the reuse of already designed components and sub-systems. This paper presents methods and tools aimed at extending structured design methodologies to behavioral synthesis, allowing modular design and design reuse. This methodology is illustrated using AMICAL, an architectural synthesis tool, and a design example. The design is first decomposed hierarchically into a top controller using a set of sub-systems. AMICAL is then used for the design of one sub-system (a fixed-point unit) which is used in a second step as a functional unit, by AMICAL, for the synthesis of the full design.