The big idea of the antenna, and it took me a while to understand the consequences, is as follows. It is better understood in the case of the reception I will take, but the effect is always reciprocal.
The local ambient electromagnetic field from a remote transmitter creates an induced current in the antenna. Lenz's law causes this induced current to create an electromagnetic field that opposes the ambient field. However, in a field, we have energy: the energy density is 1/2(Ɛ.E²+B²/µ), and the energy is conserved. So where does the energy from the ambient field go when the current in the antenna creates a field that opposes it? Well, in the antenna current! So, thanks to the current induced by the external field, the more the antenna produces a field that opposes the ambient field in the largest possible volume, and the more energy is collected from this field. This needs the adaptation of the impedances of all the components constituting the circuit as a whole: receiver input+line+antenna.
This also introduces the idea of the electrical antenna volume, which is to be increased. With good design it can go far beyond the physical volume occupied by the antenna (this also explains, but only in reception, the considerable gain that can be expected from negative impedances, which by reinjecting energy opposite the ambient field, allow more energy to be recovered in the current. But that's another story...) Of course if we want only a confined local field, for exemple for NMR applications, we don't need these considerations. It's another problem, especially because of standing waves.
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"Open your mind, but not like a trash bin"
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