In RF impedance matching, the load impedance should be what with respect to the source impedance to minimize reflections?

• A. The complex conjugate of the source impedance
• B. The same as the source impedance
• C. The reciprocal of the source impedance
• D. Purely real

Answer: (A)

In RF impedance matching, you minimize reflections by making the load compensate the source’s impedance exactly in the complex sense. If the source impedance is Zs = Rs + jXs, the load should present ZL = Rs − jXs. This complex-conjugate relationship cancels the reactive part as seen by the source, so the current drawn from the source is in phase with the voltage and the input looks purely real. That maximizes real power transfer and greatly reduces reflected waves. When the source has no reactance (Xs = 0), this reduces to matching the load to the same real resistance, which is intuitive. Matching only the real part or using the reciprocal does not eliminate the reactive component, so reflections persist.