Definition Check: Transmission-Line Discontinuity A transmission-line discontinuity is defined as any interruption in the uniformity (geometry or material parameters) of the line. Is this statement correct?
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ATrue
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BFalse
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CTrue only for coaxial lines, not waveguides
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DTrue only if the interruption is resistive
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EFalse unless the VSWR exceeds 2
Answer
Correct Answer: True
Explanation
Introduction / Context:Accurate matching and modeling at RF/microwave frequencies requires recognizing what counts as a discontinuity. Discontinuities cause reflections and local field distortions, affecting return loss and bandwidth.
Given Data / Assumptions:
- A “uniform” line has constant R, L, G, C per unit length or constant cross-section and material fill.
- Any geometric, dielectric, or conductive change breaks uniformity.
- We are considering general transmission structures: coax, microstrip, stripline, and waveguide.
Concept / Approach:
A discontinuity is any localized change in impedance or propagation constant. Examples include steps in width/height, connectors, bends, junctions, posts, irises, tapers, or dielectric inserts. These can be modeled by equivalent reactive/ resistive networks that create reflections (nonzero Γ) even if losses are low.
Step-by-Step Solution:
1) Start from uniform line: Z0 and β constant → no reflection.2) Introduce change (e.g., width step): Z0 changes locally → Γ ≠ 0 → discontinuity exists.3) Therefore, the definition stating “any interruption in uniformity” is correct.Verification / Alternative check:
Field solvers and Smith chart experiments verify that even small geometry changes introduce measurable S11, demonstrating discontinuity behavior.
Why Other Options Are Wrong:
Limitations to coax (C) or “resistive only” (D) are unfounded; discontinuities can be purely reactive. Threshold VSWR (E) is arbitrary; any nonzero reflection qualifies.
Common Pitfalls:
Ignoring very small features as “negligible”; at high frequency, even small steps can matter.
Final Answer:
True