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Quantification of Loss Due to Evanescent Phenomenon in Underground-to-Aboveground RF Communication

Posted Jul 29, 2025, 5:45 p.m. EDT Electromagnetics, Ray Optics, RF & Microwave Engineering Version 6.2 0 Replies

Poonam Maurya

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Hi everyone,

I am simulating underground-to-aboveground (UG-to-AG) RF communication using the RF Module in COMSOL. Specifically, I placed a dipole antenna underground and evaluated the power both just below and above the soil-air interface to study the evanescent wave phenomenon and quantify related losses.

As we know, evanescent waves occur when the incident angle exceeds the critical angle at a dielectric boundary (in this case, from soil to air), preventing the wave from propagating into the upper medium.

However, in the case of a dipole antenna, which emits a spherical radiation pattern, it is unclear how to define or compute a unique incident angle. I am wondering:

What is the correct way to verify the presence of evanescent waves in this scenario?

Can the incident angle be inferred from the phase of the field (e.g., arg(emw.Ez)) or perhaps by tracking the direction of the Poynting vector near the interface?

How do we quantify evanescent loss, and how can we distinguish it from reflection loss in COMSOL simulations?

Any guidance or references on how to confirm evanescent behavior and quantify associated losses in full-wave simulations like COMSOL would be highly appreciated.

Thanks in advance!

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