Reflections from bends in a printed conductor

An electrical model which is known to characterize a reactive discontinuity on a lossless transmission line is used 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 simple 90° bend is shown to be approximately 4.5% at an 80% signal risetime of 0.123 ns. Scaling laws for other risetimes and dielectrics are developed. A 180° bend and a mitered 45° 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, simple 90° 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