How important is the antenna?

source：pttcn.net



Antenna is a relatively common equipment, widely used in broadcasting, television, radio communication, radar, navigation, electronic countermeasures, remote sensing, radio astronomy and other fields. An antenna is a device that can effectively radiate electromagnetic waves in a specific direction in space or can effectively receive electromagnetic waves from a specific direction in space. All devices that transmit signals through electromagnetic waves must carry an antenna.

Some friends are curious that walkie-talkies are nearly half a century earlier than mobile phones, but today's mobile phones have no external antenna, but walkie-talkies still use a long antenna. Why is this? In fact, most of the first old-fashioned mobile phones were equipped with an antenna. Later, with the evolution of technology, the antenna was hidden inside the mobile phone.

First of all, we should clarify a concept: the higher the frequency, the shorter the wavelength, and the shorter the antenna.

The mobile phones we usually use generally communicate on the two frequencies of 900MHz and 1800MHz, while the working frequency of our civilian walkie-talkies is between 409 and 410MHz. In order to transmit the radio signal as much as possible, a longer antenna is needed.



Basic parameters

In our daily life, we find that intentionally or unintentionally turning or stretching the antenna of the radio or TV will affect the signal quality. In fact, the parameters of the antenna are changed, which affects the reception of electromagnetic waves. The transmission and reception effect of the antenna is closely related to the parameters of the antenna. Below we introduce some basic parameters of the antenna.


1. Working frequency

The antenna always works in a certain frequency range (bandwidth), which depends on the requirements of the index. The frequency range that meets the index requirements is the operating frequency of the antenna. Various wireless standards are different, and the frequency bands used by operators are different, so you need to choose an antenna with a suitable frequency band.


2. Gain

Antenna gain refers to the ratio of the power density of the signal generated by the actual antenna and the ideal radiating unit at the same point in space under the condition of equal input power. The gain is closely related to the antenna pattern. The narrower the main lobe of the pattern and the smaller the side lobe, the higher the gain. Antenna gain is used to measure the ability of an antenna to radiate electromagnetic waves in a specific direction. It should be noted that the antenna itself does not increase the energy of the radiated signal, it just concentrates the energy in a certain direction through the combination of antenna elements and changing its feeding mode.


3. Bandwidth

Bandwidth is another basic antenna parameter. Bandwidth describes the range of frequencies within which the antenna can correctly radiate or receive energy. Antennas with very small bandwidth cannot be used for broadband applications.



In real life, in order to meet various practical needs, engineers invented various antennas. The most common is this kind of long antenna, called a vertical monopole antenna (Vertical Antenna), also called a GP antenna, which is commonly found in handheld devices.
 

This is the famous Yagi antenna, which is composed of multiple units and has strong directivity. The more directors, the stronger the directivity and the higher the gain.
 

We often see this kind of dish antenna on residential roofs. This is a highly directional antenna specially used for long-distance communication. It has an extremely narrow beam width and a high gain value. It can also be called a high-gain directional antenna.
 
In fact, although the antenna types are dazzling, the working principles are actually the same.