An antenna is just a wire? If you only know this, you are wrong!

Antennas and wires are two critical but distinct components in wireless communications systems. They each perform important tasks, although their functions and operating principles are very different.

Wireless communication is one of the main themes of intelligent civilization. In modern communication, wireless communication occupies an unshakable position. In radio communication systems, there is a vital part, that is, the antenna.

Wireless communication Antenna

The most common radio antennas are two metal rod-shaped conductors. So, There are people may have thought, can ordinary wires be used instead of these antennas?

Let's discuss the similarities and differences between antennas and wires. First, let's discuss their similarities:
(1) Antennas are made of metal materials because current will pass through the antenna;
(2) The alternating current in the antenna and the conductor will generate an alternating electromagnetic field around them;
(3) When the antenna and the conductor are energized, their absolute temperature will rise;
It seems that the physical properties of antennas and wires have many similarities. However, the reason why an antenna is called an antenna is that it carries an important function: it is an efficient transducer of the guided wave and the free wave in space, as shown in the figure below:

Antenna transmission

To understand the above sentence, we need to understand the working principle of the antenna. Here we discuss the classic dipole antenna.

The so-called guided wave is the electromagnetic wave transmitted in a planar form in the waveguide structure. The free wave in space is the electromagnetic wave radiated from the antenna. When the distance between the two poles of the dipole reaches or far exceeds the order of the wavelength of the electromagnetic wave, most of the electromagnetic wave energy is released in the form of radiation. In order to radiate the energy efficiently, we need to accurately design and manufacture the wire, including but not limited to shape, conductor length, and impedance control.

The specific differences between antennas and wires are as follows:

(1) The two poles of the antenna are called "antenna vibrators". Usually, the effect is best when the half-arm length is one-quarter of the wavelength, so there are requirements for the length of the antenna;

(2) In order to control the bandwidth, there are requirements for the thickness of the metal rod used in the antenna. Generally speaking: the thicker the pipe used, the wider the bandwidth.

(3) Impedance. The 50 ohm system is used in my country's civil radio system, so the impedance of the antenna also needs to be controlled at 50 ohms.

After several centuries of development, the antenna family has become a huge family. It can be roughly divided into: end-fire antenna, loop antenna, dipole antenna, and aperture antenna.

Among them, the end-fire antenna includes: dielectric rod antenna, Yagi antenna (Figure 2), log-periodic antenna, etc.

Dipole antenna includes: diamond antenna, biconical antenna, etc.

Aperture antenna includes: lens antenna, reflector antenna, etc.

These antennas have different characteristics, which are reflected in polarization direction, gain, resolution, volume, etc.