Behaviour of EM-wave near a non-resonant antenna

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SUMMARY

The behavior of electromagnetic (EM) waves interacting with non-resonant antennas involves scattering rather than simple reflection or transmission. When an EM wave reaches a conductive antenna, a current is induced in the material, leading to re-radiation of the signal and partial reflection, which distorts the local field. Resonant structures, in contrast, can generate higher induced currents and create interference patterns, necessitating that a rod or near-resonant structure be slightly longer than its resonant length to effectively act as a mirror for specific frequencies.

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  • Understanding of electromagnetic wave propagation
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  • Basic principles of signal scattering and re-radiation
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Timothy S.
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What will happen with the electromagnetic wave reaching an antenna when this antenna is not resonant on the frequency of the wave: will it reflect from antenna or pass through it?

Thank you
 
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It does not have to be a non-resonant antenna, any conductor will scatter a signal.

A current will be induced in the conductive antenna material, that will, in effect, re-radiate the signal. The partial reflection will add to the incident wave, distorting the field locally.

Resonant structures can build up higher induced currents, forming interference patterns throughout the region.
 
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May I mention that if we want a rod or near-resonant structure to act as a mirror, then it must be resonant at or a little below the require frequency. This often means it should be a little longer than the resonant length, and shorter rods tend to be transparent.
 
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