Question
What impedance does a 1/8-wavelength transmission line present to an RF generator when the line is shorted at the far end?
Answer Options
- A) A capacitive reactance
- B) The same as the characteristic impedance of the line
- C) An inductive reactance
- D) Zero
Correct Answer: C
Explanation
When a short-circuited stub is used (a length of line shorter than ¼ wavelength), the line behaves reactively. A shorted ¼-wave line looks open-circuited (infinite impedance); thus, a shorter length must present something less than an open circuit.
When a ⅛-wavelength transmission line is shorted at the far end (Z_L = 0), the line transforms this short circuit into a low-to-medium inductive reactance at the input end (Z_{in} = +jX_L). This property is exploited in antenna matching and filter circuits where a specific amount of inductive reactance is required.
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