AdvancedA-007-002-001
What kind of impedance does a quarter wavelength transmission line present to the source when the line is shorted at the far end?
B
Answer
Interference, EMC, and safety
Type
A
The same as the output impedance of the source
B
A very high impedance
C
The same as the characteristic impedance of the transmission line
D
A very low impedance
Answer Notes
A quarter-wavelength transmission line has a unique property: it acts as a perfect impedance inverter. It transforms the impedance attached at one end to its exact opposite at the other end.
When the far end is shorted (zero impedance), the quarter-wave line transforms that zero impedance into an infinitely high impedance (an open circuit) at the source end. This makes quarter-wave shorted stubs highly useful as RF chokes, allowing DC to pass while blocking RF energy.
If the far end were open instead of shorted, the quarter-wave line would invert it into a very low impedance (a short) at the source.
Previous · A-007-001-011
A Smith Chart is useful:
Next · A-007-002-002
What kind of impedance does a quarter wavelength transmission line present to the source if the line is open at the far end?