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In typical high-frequency transmission-line modeling (RLCG model), which primary distributed parameter is often negligible under many practical conditions?

Difficulty: Easy

Correct Answer: G (shunt conductance)

Explanation:


Introduction / Context:
Distributed-parameter models describe lines using R, L, C, and G per unit length. Understanding which parameters dominate guides low-loss approximations and design choices across frequency bands.


Given Data / Assumptions:

  • Dielectric is low-loss (tan δ small).
  • Conductor losses and skin effect may be present but manageable.
  • Typical RF/microwave coaxial, microstrip, or twin-lead environments.


Concept / Approach:
At many RF frequencies with quality dielectrics, shunt conductance G (which models dielectric leakage) is very small compared to susceptance from C and reactance from L. Hence, the well-known 'low-loss line' approximation treats R and G as small compared to ωL and ωC, with G often the smallest of the four.


Step-by-Step Solution:

Telegrapher parameters: R (Ω/m), L (H/m), C (F/m), G (S/m).Dielectric loss modeled by G is minimal for high-quality, dry dielectrics; tan δ ≈ ωC/G is low.Thus, for many practical lines, G is negligible first; sometimes R is also small but not as negligible as G in many PCB and coax cases.


Verification / Alternative check:
Attenuation constant α ≈ (R/2)√(C/L) + (G/2)√(L/C); for low-loss lines, the G-term is frequently orders of magnitude smaller than the R-term.


Why Other Options Are Wrong:

L and C define the line's phase velocity and characteristic impedance and are never negligible.R can be small, but conductor loss is often significant compared with G, especially with skin effect.


Common Pitfalls:

Assuming G is always zero; humidity or lossy dielectrics can increase G at low or very high frequencies.


Final Answer:

G (shunt conductance)
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