Allerton 2021: The Schelkunoff-Smith Chart and How Near Fields Work

Slides

Today, I’m presenting my talk on the Schelkunoff-Smith Chart and How Near Fields Work at the 2021 Allerton Antenna Applications Symposium.

Ideal electromagnetic waves include synchronized electric and magnetic waves conveying equal amounts of electric and magnetic energy at the speed of light. The ratio of the electric to magnetic field is the free-space impedance, 376.7 ohm. Close to the source, however, the electric and magnetic components of the wave are no longer synchronous. When the waves are in phase, they carry energy away. When the waves are out of phase, they convey energy back to the source. When the impedance of the waves is no longer that of free space, they no longer carry energy at the speed of light. These fascinating relationships may be portrayed and understood by applying a Smith Chart to plot the relative amplitudes and phases of the near-fields as defined by Schelkunoff in his classic paper on impedance. We can further compare the graphical treatment of the Smith Chart to time-domain plots of the electric and magnetic waves to gain further insight to how the amplitudes and phases of the waves cooperate to decouple energy and radiate it away.

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