Reflections from Bends in a Printed Conductor.

An electrical model which is known to characterize a reactive discontinuity on a lossless transmission line is applied to determine the maximum signal reflection from a bend in a printed microstrip transmission line. For printed wiring board applications using the usual FR4 dielectric, the maximum signal reflection from a 90C bend is shown to be approximately 4.5% at an 80% signal rise time of 0.123 ns. Scaling laws for other rise times and dielectrics are developed. A 180C bend and a mitered 45C bend are also treated. The electrical model yields signal reflections which agree well with corresponding experimental results. for bit rates as high as a few gigabits per second, and suitable dielectrics, 90C bends are still adequate. For much higher bit rates and more gradual bends, other parasitics also become important and limit the performance of electrical interconnections.