Dielectric constant of air with temperature change

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Discussion Overview

The discussion focuses on the relationship between the dielectric constant of air and its temperature, exploring how temperature and atmospheric pressure may influence this property. Participants are interested in both theoretical and practical implications, particularly in the context of measurements involving antennas.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant seeks a formula that relates the dielectric constant of air to temperature and atmospheric pressure.
  • Another participant suggests using the capacitor formula C=Ae/d but expresses uncertainty about the original question.
  • A participant presents a scenario involving two antennas at different distances and asks how a temperature change from 25 C to 15 C would affect the phase delta, emphasizing the need for knowledge of the dielectric constant to compute the velocity factor.
  • One participant intuitively expects that permittivity increases with temperature and references the relationship between relative permittivity and electric susceptibility, suggesting that existing literature may address this dependence.

Areas of Agreement / Disagreement

Participants do not appear to reach a consensus on the specific relationship between temperature and the dielectric constant of air. Multiple viewpoints and uncertainties remain regarding the effects of temperature and the appropriate formulas to use.

Contextual Notes

There are limitations in the discussion, including the lack of specific formulas for calculating the dielectric constant of air as a function of temperature and pressure, as well as unresolved assumptions about the conditions under which measurements are taken.

Antenna_Ed
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I'm looking to see how much the dielectric constant of air will change mostly as a function or air temperature.

Is there a formula that outputs air dielectric as a function of temperature or atmospheric pressure?
 
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If using a capacitor you might be able to use C=Ae/d but I really don’t understand your question fully
 
Let's pretend I have a source antenna outputting a 1 GHz. I have two receive antennas on the main lobe. One is 10 meters away and the other is 11 meters away. I do my measurement at 25 C. I'm going to get some phase delta between these two antennas.

Now if the temp is 15 C when I make the measurement, what will the phase delta be? I'm ignoring everything else at the moment and only care about the effect of air. If I knew the dielectric I can compute the velocity factor and know the magnitude of change.
 
Intuitively, I would expect permittivity to increase with an increase in temperature. The relative permittivity is directly related to electric susceptibility, and I believe there are a number of publications that exist discussing the subject of the dependence on electric susceptibility of air with temperature. I haven't done a lot of research on the subject, but I would start there.
 

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