In this book are introduced the called Coherently Radiating Periodic Structures – CORPS, to set its main behaviour characteristics and to explore applications for this novel technology on both antenna field and Beam Forming Networks- BFN. The CORPS structures are based on the analysis of the ideal coupling effects over periodic structures. Using results obtained in this analysis, the main behaviour features governing a CORPS based structure are defined. In the same way, using both application-prototypes and proof-of-concepts are experimentally corroborated the proposed principles for a structure based on CORPS. One of foremost fields where the CORPS concepts could be successfully applied is the one related with the Beam Forming Networks. For this reason, a specific methodology for the design of Beam Forming networks based on CORPS concepts is proposed. This methodology is denominated Coherently Radiating Periodic Structures- Beam Forming Network – CORPS-BFN. CORPS-BFN is useful for designing, among others, Phased Arrays systems, in particular those related to multiple-beam systems improving their overal performance.