Question
What impedance does a 1/8-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) An inductive reactance
- C) A capacitive reactance
- D) Infinite
Correct Answer: C
Explanation
When an open-circuited transmission line stub is used (a length of line shorter than one quarter wavelength), the line again behaves reactively. An open ¼-wave line looks short-circuited (zero impedance); thus, a shorter length must present a low-to-medium reactance that is not zero.
When a ⅛-wavelength transmission line is open at the far end (Z_L = \infty), the line transforms this open circuit into a low-to-medium capacitive reactance at the input end (Z_{in} = -jX_C). This property is used in matching stubs and tuned circuits where a specific amount of capacitive reactance is required.
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