Multilayer 180 $^{\circ}$ Coupled Line Hybrid Coupler

This paper presents a theoretical analysis of a 180^deg hybrid coupler based on coupled lines. The analysis is applicable for the case where the non-TEM nature of coupled lines must be considered. The method used to analyze the coupler is based on an analytical T matrix approach, which provides suitable expressions for the design of the coupler. The design procedure is demonstrated by the fabrication of a 24-GHz coupler using low-temperature co-fired ceramic. The realized coupler has non-interspersed inputs and outputs, reduced substrate area and robustness to layer misalignment. The measured characteristics are in good agreement with simulations and demonstrate good performance of the fabricated coupler. An application example of the hybrid coupler in a compact-sized phasing network for an in-phase/quadrature mixer is also described.