directional coupler-HFSSDirectional Couplers [1] THE QUADRATURE (90) HYBRID The Hybrid coupler is often made of microstrip or stripline as shown in Figure 1. The microstrip form is also pictured in Figure 2. These couplers are 3 dB directional couplers with a 90 phase difference between the outputs of the through and coupled lines. It is also known as a branch-line hybrid. Figure 1. Geometry of a Quadrature Hybrid coupler. [1] Figure 2. Photograph of a microstrip Quadrature Hybrid coupler. [1] Referring to the geometry of Figure 1, the ideal branch-line coupler, with all ports matched and power entering port 1, has evenly divided outputs at ports 2 and 3 with a 90 phase difference between them. The isolated port (port 4) has no power exiting it. The resulting [S] matrix is then given by (1) 0 j 1 0 1 j 0 ……