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 degrees 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 degrees bend and a mitered 45 degrees 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 degrees 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.<
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