EMC Question of the Week: November 22, 2021

TEM Cell Measurement

If a plane wave propagating in a 50-Ω TEM cell has an electric field strength of 100 V/m, the magnetic field strength is approximately 

  1. 0 A/m
  2. 0.27 A/m
  3. 2.0 A/m
  4. 3.77 A/m


The correct answer is “b.” The ratio of the electric-field strength to the magnetic field strength for a plane wave propagating in air is about 377 Ω. An electric-field strength of 100 V/m corresponds to a magnetic-field strength of (100 V/m) / (377 Ω) = 0.27 A/m.

Note that, in this case, 50 Ω refers to the characteristic impedance of the transmission line. The characteristic impedance is the ratio of the septum voltage to the septum current associated with a forward traveling wave.

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