A _____ reflection will occur if impedances are slightly different.

A _____ reflection will occur if impedances are slightly different.

• A. Large
• B. Small
• C. Moderate
• D. None

Answer: (B)

The main idea is that reflections on a transmission line come from impedance mismatch, and how big the reflection is depends on how different the load is from the line. The reflection coefficient, which determines the amount of reflected energy, is gamma = (ZL - Z0)/(ZL + Z0). When ZL equals Z0, gamma is zero and there’s no reflection. If the impedances are only slightly different, gamma is a small number, so only a small portion of the wave is reflected. That’s why a small reflection occurs when impedances differ slightly. For example, with Z0 = 50 ohms and ZL = 55 ohms, about 4.8% of the voltage is reflected (and even less in power). As the mismatch grows, the reflection becomes larger; a large mismatch could yield a large reflection, while a perfect match yields none.

The main idea is that reflections on a transmission line come from impedance mismatch, and how big the reflection is depends on how different the load is from the line. The reflection coefficient, which determines the amount of reflected energy, is gamma = (ZL - Z0)/(ZL + Z0). When ZL equals Z0, gamma is zero and there’s no reflection. If the impedances are only slightly different, gamma is a small number, so only a small portion of the wave is reflected. That’s why a small reflection occurs when impedances differ slightly. For example, with Z0 = 50 ohms and ZL = 55 ohms, about 4.8% of the voltage is reflected (and even less in power). As the mismatch grows, the reflection becomes larger; a large mismatch could yield a large reflection, while a perfect match yields none.