The receiving ability of a dipole antenna is much greater than what is attained when doing calculations involving a plane wave interacting with its actual size.

Why is this? How can an antenna pull energy from a surrounding area beyond its physical interface?


I understand correctly that you are aware of the empirical fact that an antenna rod can be many times smaller than the wavelength it receives?

The answer has to do with understanding how a radio wave is made and what the constituents of these waves are.

Generation of a radio wave

It is state of the art that a modified LC circuit in unit with a wave generator is capable of radiating at the frequency of the generator used.

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In detail, the surface electrons on the rod are accelerated back and forth by the electric potential of the generator and emit photons at each acceleration. All photons together form the radio wave.

For all emitted photons, their electric field component and their magnetic field component are oriented in the same direction for half a period of the wave generator. Depending on the more or less resonant length of the antenna rod, the number of emitted photons follows more or less a sine curve; if the electric potential of the generator is zero, no acceleration of the electrons takes place and no photons are emitted. (On the carrier frequency, information is modulated onto the radio wave, be it a broadcast signal for music or be it a Wireless LAN communication.)

Receiving a radio wave

Could a thermal source like a light bulb be used for wireless communication? Yes, of course. Install a switch in the circuit and turn the light bulb on and off periodically. Take a photodiode and receive the carrier frequency. Resonate the diode with an electronic device and you will be able to filter the light from the bulb behind the noise of the light surrounding you. Last but not least, if you vary the frequency a little (this is only one of the technical possibilities of it), you will be able to encode some information.

But the functioning of a photodiode and communication in the light range is not what you are interested in.

As mentioned above, the photons of a radio wave are all polarized together. They are not a thermal source with randomly emitted photons. The common electric field of the emitted photons can be measured. All you need is a conductive piece of metal.

The photons drive the electrons in the metal back and forth, and an electronic device (again resonant) filters out the information encoded on the radio station. Of the billions of photons emitted by the antenna rod, only a tiny fraction is received by your mobile phone or Bluetooth device.

All others is the art of engineering. The signal is amplified and separated from interference and noise. For this you need a power source. A battery or a solar cell. To get enough photons, you would have to operate your device directly in front of the transmitting antenna. This is dangerous. A strong source emits radiation in wavelengths that are dangerous for your biological cells (risk of cancer). This does not apply to transmitting antenna from your mobile phone, the source is too weak.

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