Enlarging the operating frequency band of 0-dB directional couplers by using branch-line structures of a special type is discussed. Analysis of the basic configuration by the even-odd mode decomposition technique is performed. An experimental verification is presented. INTRODUCTIONRealization of crossovers is a particular problem in the design of microwave integrated circuits. In many cases, when a high isolation between crossing strips is required in a rather large frequency band, it is preferable to avoid a trivial separation of the strips by a dielectric layer. Moreover, it cannot be sometimes realized due to technological reasons. For example, the technological process of fabrication of hightemperature superconducting planar circuits does not provide layered structures, such as superconductor-dielectric-superconductor .It is well known that a single-layer analog of the crossover is the 0-dB forward-coupled directional coupler @C) [l], [2]. The branch-line configurations are of main practical interest for this purpose. Different versions of 0-dB branch-line DC are known. The three-branch DC ( Fig.1-a)