How does a Large Loop Antenna work physically?

Question

I am learning about loop antennas at the moment. I read that the response of a small loop Antenna is proportional to the rate of change of magnetic flux through the loop which causes a uniform current distribution in the loop. This would be Faraday's law. However, then we got a large loop (wavelength is as big as the circumference); how do we describe the interaction? Let's say, there is an incident electromagnetic wave going through a large loop. Can we still use Faraday's law to describe the response and is it the same response as in the case of a small loop?

This might a stupid question. I read in some books that small loops can be described using Faraday's law but they don't use Faraday's law to describe big loops.

Answer 1

In short, yes: Faraday's law describes what's happening for the large loop antenna as well. A transverse EM wave induces a current in the loop. It's Faraday all the way down for all EM/antenna interaction for that matter.

An aside: you can think of a full wave loop as a stretched-out folded dipole.

• Both have maximum current nodes at the feed point and the point directly opposite the feed point
• Both have relative nulls coming off the "ends" (in the loop the "end" is the current minimum ~1/4λ from the feed point in each direction)

Feedpoint impedance for a full wave loop is about half of the 300Ω impedance of a folded dipole... but that's from memory and I'll come back and correct this after I get a moment to check.