How do antennas catch the correct radio signal in the air?

Question

Radio signals come to antennas from certain directions. How does the antenna process of receiving the signal in the air work? How does a certain antenna receive this electromagnetic field as the radio signal travels through the air? Why does that antenna receive it and not another conductor? Also, doesn't an electromagnetic signal get lost when it is received by other antennas before it reaches the target antenna?

Specifically, I ask the following. How is the signal from an antenna directed towards the target? How is the signal coming to the target antenna pulled towards itself by the antenna?

Answer 1

How do antennas catch the correct radio signal in the air?

They don't. They catch all the signals that are within their operating band (which is generally much wider than a single broadcasting channel).

Then the receiver electronics that they are connected to selects an individual channel to receive, amplify, and demodulate or decode.

How does a certain antenna receive this electromagnetic field as the radio signal travels through the air?

It depends on the geometry of the antenna. An antenna made up of a long straight wire works by the electric field component of the EM wave driving conductors in the antenna back and forth. An antenna made up of a loop of wire works by the magnetic field component of the EM wave inducing an emf around the loop. Other shapes are more complicated but typically work by reflecting the EM field from a large area onto a smaller antenna that works like one of the above.

Why does that antenna receive it and not another conductor?

Other conductors can. That's why electrical engineers spend a lot of time worrying about electromagnetic compatibility and electromagnetic compliance.

Also, doesn't an electromagnetic signal get lost when it is received by other antennas before it reaches the target antenna?

Typically antennas aren't that efficient at extracting power from the EM wave. Also, even if they did completely absorb the power that reached them, the wave would refract around them after a few wavelengths and be available for a second antenna to receive.

How is the signal from an antenna directed towards the target?

This is a very complicated question, but it basically involves designing the transmitting antenna so that radiation from it interferes constructively in the direction you want to send a signal and destructively in the directions you don't want to send the signal.

How is the signal coming to the target antenna pulled towards itself by the antenna?

It isn't. The receiving antenna just receives the (usually tiny) portion of the transmitted signal that happens to reach its actual surface.

Answer 2

The broadcast signal is not directed in most cases. It goes in all directions. That is why millions of people can listen to the same radio station.

Broadcasts are made on narrow frequency bands, and it is the job of the receiver to be tuned to a certain frequency and filter the desired signal from the general cacophony of radio signals that exists in the ambient environment.

Answer 3

To add to The Photon's answer:

A clever antenna design can actually behave significantly "larger" than its physical cross-section for signal capture, as follows. We can place a "dummy antenna" that is not connected to anything a short distance in front of the actual antenna. The incoming radio wave strikes the dummy element first and wastes some time interacting with it. That portion of the plane wave front is now slightly phase-delayed relative to the rest of the wave and the wave then refracts (bends in) slightly around the dummy element- so more of the plane wave strikes the "active" antenna behind it.

We can add more dummy elements like this in front of the active element to diffract more and more of the incoming plane wave into the active element, yielding an antenna that now consists of a long horizontal beam (bristling with little antenna elements sticking out from its sides) that you point at the broadcasting antenna. This is the principle behind old-school rooftop TV antennas from the pre-cable era and is called the Yagi-Uda design after its Japanese inventors.