Standing Wave Ratio and Frequency Dependence in Transmission Lines

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Discussion Overview

The discussion focuses on the relationship between standing wave ratio (VSWR) and frequency in transmission lines, particularly how these factors interact with characteristic impedance and load impedance. The scope includes theoretical considerations and mathematical reasoning related to transmission line behavior.

Discussion Character

  • Exploratory
  • Technical explanation
  • Mathematical reasoning

Main Points Raised

  • One participant questions whether the standing wave ratio depends solely on the characteristic impedance and load impedance, suggesting that it might not change with frequency.
  • Another participant asserts that the VSWR is influenced by the reflection coefficient, which is dependent on load impedance and characteristic impedance, and notes that load impedance typically varies with frequency, implying that VSWR will also vary.
  • There is a proposal regarding the input impedance at the load being equal to the load impedance, with a suggestion that certain mathematical terms may cancel out under specific conditions (e.g., at z = 0).
  • A repeated point raises the same question about the cancellation of terms and whether this leads to a logical conclusion regarding the behavior of the system.

Areas of Agreement / Disagreement

Participants express differing views on the dependence of VSWR on frequency, with some suggesting it is constant while others argue it varies due to changing load impedance. The discussion remains unresolved regarding the implications of these viewpoints.

Contextual Notes

The discussion does not clarify the assumptions regarding the nature of the load impedance or the specific conditions under which the proposed mathematical cancellations occur.

seang
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If I have a section of transmission line, with a characteristic impedance Z0, how does the standing wave ratio in that section change as a function of the frequency of operation?

Doesn't the stading wave ratio just depend on the characteristic impedance of the line, and the load impedance?
 
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Yes, the VSWR ratio depends only on the magnitude of the reflection coefficient, which is a function of the load impedance and characteristic impedance. However, in general, the load impedance will be a function of frequency, so the VSWR will be as well.
 
Finding the Input Impedance at z = 0 (the load) is equal to the load impedance, maybe? If so, don't the tan(Bl) all cancel anyway since l = 0?
 
seang said:
Finding the Input Impedance at z = 0 (the load) is equal to the load impedance, maybe? If so, don't the tan(Bl) all cancel anyway since l = 0?

Which would make sense wouldn't it?
 

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