Question
How does an impedance-matching circuit transform a complex impedance to a resistive impedance?
Answer Options
- A) It introduces negative resistance to cancel the resistive part of impedance
- B) It introduces transconductance to cancel the reactive part of impedance
- C) It cancels the reactive part of the impedance and changes the resistive part to the desired value
- D) Reactive currents are dissipated in matched resistances
Correct Answer: C
Explanation
A complex impedance (Z = R + jX) consists of a resistive component (R) and a reactive component (jX). For maximum power transfer and minimal Standing Wave Ratio (SWR), an antenna system’s complex impedance must be transformed into a purely resistive impedance that matches the 50 \Omega characteristic impedance of the feed line.
An impedance-matching circuit achieves this transformation in two steps: first, it introduces an equal and opposite reactance to cancel the reactive part of the impedance (e.g., adding an inductor to cancel existing capacitive reactance). Second, the matching circuit acts as a transformer to change the resistive part to the desired value (e.g., transforming 35 \Omega to 50 \Omega). This two-step process results in the ideal resistive load.
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