Question
What impedance does a 1/4-wavelength transmission line present to an RF generator when the line is open at the far end?
Answer Options
- A) The same as the characteristic impedance of the line
- B) The same as the input impedance to the generator
- C) Very high impedance
- D) Very low impedance
Correct Answer: D
Explanation
The Quarter-Wave Transformer principle states that a ¼-wavelength section of transmission line acts as an impedance inverter. An open circuit (infinite impedance) is one extreme load that is easily inverted.
When a ¼-wavelength transmission line is open at the far end (Z_L \approx \infty), the line inverts this open circuit, transforming it into a Very low impedance (theoretically zero, or a short circuit) at the input end. This open quarter-wave stub acts as a series-resonant circuit.
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