Reflections and matching are closely related to loop antenna theory, but different enough to warrant their own discussion. When a PCB trace turns a corner at a 90 angle, a reflection can occur. This is primarily due to the change of width of the trace.
At the apex of the turn, the trace width is increased to 1.414 times its width. This upsets the transmission line characteristics, especially the distributed capacitance and selfCinductance of the trace resulting in the reflection. It is a given that not all PCB traces can be straight, and so they will have to turn corners.
Most CAD systems give some rounding effect on the trace. Sharp 90_ corners in traces are a relic of the tape up days of PCB layout. The rounding effects of CAD programs, how-ever, still do not necessarily maintain constant width as the trace rounds the corner. It shows progressively better techniques of rounding corners. Only the last example maintains constant trace width and minimizes reflections. Most CAD programs now sup-port these methods, but they can entail a little more work to master.
