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Knowles – Balancing Performance with Compact Quadrature Hybrid Couplers


Quadrature hybrid couplers are basic building blocks for many RF and microwave systems. For these couplers, the input splits into two output signals, of equal magnitude, with a 90 degree phase difference. Quadrature hybrid couplers provide improved input match for unbalanced loads. Energy splits evenly between outputs, and some energy is reflected back due to mismatch. For example, in Figure 1, there is a 90 degree phase difference between the two outputs, so the energy reflected at point A is 180 degree out of phase and cancels at the input port. At point B, the energy is in phase and sums at the isolated port, which is terminated.