The implementation of wideband 90° hybrids on non-optimal substrates

Abstract

A new technique to implement wideband 90° hybrid coupling profiles on non-optimal substrate configurations is presented. The technique uses an impedance taper over the whole length of the hybrid to remove the restriction of a substrate defined maximum coupling coefficient at crossover, thus resulting in much more flexibility for the implementation of hybrids on integrated printed circuit boards. The choice of board thicknesses and material type no longer needs to be dominated by the hybrid, but can be optimized for other components or priorities. The flexibility provided by the technique is shown in the implementation of a 2–18 GHz hybrid on a large range of substrate thicknesses as well as on a non-optimal substrate material, for which acceptable measured performance is still obtained.