Antennas are a very common communication device in our lives. However, most people don't truly understand them, perhaps only knowing that they are used to transmit and receive signals.
Incidentally, since the Russian scientist Popov successfully invented the antenna in 1894, this device has a history of 124 years.
Today, whether it's for ordinary people's daily work and life, or for scientists conducting scientific research, we cannot do without the silent contribution of antennas.
What kind of "wire" exactly is an antenna, and why has it so thoroughly changed our lives?
In fact, the reason antennas are so powerful is because electromagnetic waves are powerful. And a major reason why electromagnetic waves are so powerful is that they are the only "mysterious force" that can propagate without relying on any medium. Even in a vacuum, they can travel freely and arrive instantaneously.
Diagram of electromagnetic wave propagation
To fully utilize this "mysterious power," you need an antenna. Simply put, an antenna is a "converter"—it transforms guided waves propagating along a transmission line into electromagnetic waves propagating in free space, or performs the reverse transformation.
The function of an antenna
What is a guided wave? Simply put, a guided wave is an electromagnetic wave that travels along a wire. How does an antenna achieve the conversion between guided waves and spatial waves?
See the image below:
Basic physics tells us that when two parallel wires carry alternating current, electromagnetic waves are radiated.
When the two wires are very close together, the radiation is very weak (the induced electromotive forces generated by the currents in opposite directions almost cancel each other out).
When the two wires are spread apart, the radiation increases (the induced electromotive forces generated by the currents in the same direction are also in the same direction).
When the length of the wire increases to one-quarter of the wavelength, a relatively strong radiation effect can be achieved!
Where there is an electric field, there is a magnetic field; where there is a magnetic field, there is an electric field. This cycle continues, resulting in electromagnetic fields and electromagnetic waves.
The diagram is shown below：
The change in the direction of current flow in the wire generates a changing electric field.
The two straight wires that generate the electric field are called dipoles.
Usually, both arms are of equal length, so they are called symmetrical dipoles.
A dipole with a length like the one shown below is called a half-wave symmetrical dipole.
Half-wave symmetric dipole antenna
Connecting the two ends of the wire together transforms it into a half-wave symmetrical folded dipole antenna.
Half-wave symmetrical folded dipole antenna
The symmetrical dipole antenna is by far the most classic and widely used antenna.To be precise, a radiating element is not a complete antenna. The radiating element is the core component of an antenna, and its shape varies depending on the antenna's design.And there are just so many different types of antennas... so many...
In the next issue, we will provide a more detailed introduction to different types of antennas and their characteristics.
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Post time: Nov-28-2025
