Novel Composite RF PCB Stack-up & Engineering for Wideband RF Cross-Overs

A Novel Composite RF PCB Stack-up which is simple, economical & manufacturable is proposed and realized. Paper also discusses design & engineering of wide band (DC to 18GHz) RF transitions and routing of RF traces in inner layers of proposed composite multi-layer printed circuit boards (PCB's) with minimum losses. Design is suited for Microwave Integrated Circuits (MICs) based applications involving multiple RF crossovers realized on single composite RF card. Design considers two traces, one direct & other transiting trace for RF crossover. The transiting trace undergoes through multiple changes in RF medium at junctions namely a) CPW/Micro-strip to Coax, b) Coax to Strip-line c) Strip-line to Coax d) Coax to CPW/Micro-strip. To ensure minimum insertion loss over required frequency band, key challenge is to provide better matching at the transitions. The Stack-up that is proposed is realized for 6 layers. RF traces are routed in 1 ^st & 3 ^rd layers. A straight RF trace is printed on 1 ^st layer & is compared with transiting RF trace of similar length. Though the work can be extended to more number of RF buried layers. Topology planning, design considerations, engineering, result analysis are discussed in this paper.