Analysis on the effectiveness of printed circuit board edge termination using discrete components instead of implementing the 20-H rule

With increasing demand for higher operating frequencies, engineers are faced with numerous obstacles during the design cycle, especially the layout of a printed circuit board (PCB). Concerns include both time and frequency domain analysis. For time domain analysis, SPICE is a favorite choice, while for the frequency domain, various field solvers are used, depending on application. There is one design concern that cannot be simulated using either SPICE or field solvers exclusively - the 20-H rule. The reason why a single simulation tool cannot be used is due to termination of an RF propagating field (frequency domain.) using transmission line theory (time domain). The placement of components on a PCB and their physical distance to the edge of the board may cause an undesired RF propagating field to be created. The paper analyzes propagating electromagnetic fields between a pair of power and return planes behaving as a transmission line. With proper analysis, one can incorporate optimal transmission line termination for RF fields using discrete components instead of blindly implementing the 20-H rule (provides the same benefit). For unique applications, the 20-H rule may be required, but only in certain locations of the PCB.