Design and Optimization of Lumped Element Hybrid Couplers

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  • Author: Ashok Srinivas Vijayaraghavan and Lawrence Dunleavy
Quadrature 3 dB hybrid couplers are widely used in microwave circuit design. The principle of a hybrid coupler is that the input power is split equaly between the coupled and through ports, with a 90 degree phase difference. The fourth (isolated) port is terminated by a 50-ohm load. Resonant quarter wavelength transmission lines are used in the distributed design approach, and several lumped element design approaches are described in the literature [1, 2]. The design method selected for this example does not use via holes, which makes it easy to implement using either a PCB-based (as in this work) or a MMIC approach. The bandwidth of this design is claimed to be better than the corresponding distributed branch-line hybrid version [1, 2], at least when using idealized L-C models.