Terminating a transmission line with its characteristic impedance helps to minimize reflections and maximize power transfer.

• A. Termination with the characteristic impedance
• B. Termination with zero ohms
• C. Leaving line unterminated
• D. High-frequency termination always increases reflections

Answer: (A)

When a signal travels along a transmission line, the amount of energy that gets reflected depends on how the load impedance compares to the line’s characteristic impedance, Z0. If the load equals Z0, the wave sees a perfectly matched load and the reflections disappear. The mathematical telltale is the reflection coefficient; it becomes zero when ZL = Z0, so there is no reflected wave and all the incident power is delivered to the load. This matching keeps the voltage and current along the line stable and maximizes the usable power transfer.

Terminating with zero ohms or leaving the line open creates large reflections (the reflection coefficient has magnitude one), producing standing waves, inefficient power transfer, and potential issues with the source due to the back-and-forth energy. Saying that high-frequency termination always increases reflections isn’t correct: the purpose of proper termination is to minimize reflections by matching the load to Z0.