Question
What is the result of increasing the Q of an impedance-matching circuit?
Answer Options
- A) Matching bandwidth is decreased
- B) Matching bandwidth is increased
- C) Losses increase
- D) Harmonics increase
Correct Answer: A
Explanation
The Quality factor, or Q, of a resonant or tuned circuit is a measure of its selectivity (sharpness). The relationship between a circuit’s Q, its resonant frequency (F_R), and its bandwidth (\Delta F) is inverse: Q = F_R / \Delta F. In the context of an impedance-matching circuit, the bandwidth (\Delta F) refers to the range of frequencies over which the circuit maintains an acceptable impedance match (e.g., SWR below 2:1).
Since the Q is inversely proportional to the bandwidth, the result of increasing the Q of an impedance-matching circuit is that the matching bandwidth is decreased. This creates a sharper tune, meaning the circuit will match the impedance over a much narrower frequency range. While a higher Q provides a steeper rolloff (often desirable for harmonic suppression), it requires constant re-tuning as the operating frequency changes.
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