Finite Ground Coplanar Waveguide (FGC) Low Loss, Low Coupling 90-Degree Crossover Junctions

Microwave and millimeter-wave integrated circuits and RF distribution networks often require two transmission lines to cross over each other. In this paper, experimental measurements and three-dimensional (3-D) finite difference time domain analysis are used to thoroughly characterize coplanar waveguide (CPW) and finite ground coplanar waveguide (FGC) 90-degree crossover junctions. It is shown that FGC crossover junctions have approximately 15 dB lower coupling than CPW crossover junctions. Furthermore, it is shown that the FGC junctions do not excite the parasitic slotline mode, whereas, the CPW junctions do excite the slotline mode. The results presented indicate that the FGC crossover junction is easier to implement and has better characteristics than the CPW crossover junction.