The antenna knowledge that the communicator must know is here!

An antenna is a transducer that transforms a guided wave propagating on a transmission line into an electromagnetic wave propagating in an unbounded medium (usually free space), or vice versa. A component used in a radio device to transmit or receive electromagnetic waves.

The ratio of the total input power of the antenna is called the maximum gain factor of the antenna. It is more comprehensive than the antenna directivity coefficient to reflect the effective utilization of the antenna to the total RF power. And expressed in decibels. It can be mathematically proved that the maximum gain coefficient of the antenna is equal to the product of the antenna directivity coefficient and the antenna efficiency.

First, the invention of the antenna

The antenna was invented by the Russian scientist Popov.

In 1888, when the 29-year-old Popov learned that the famous German physicist Hertz discovered the electromagnetic wave, the young scientist who had decided to promote the electric light said to his friends: "I used my life to install the electric light, for the vast For Russia, it only illuminates a very small corner: If I can direct magnetic waves, then I can fly across the world!"

So he immersed himself in research and launched an impact on the new goal.

In 1894, Popov made a radio receiver. The core of this receiver uses an improved metal chip detector, and Popov uses a bell for terminal display. The hammer of the bell can loosen the metal chips in the detector. The bell is driven by an electromagnetic relay. When the metal detector detects an electromagnetic wave, the relay is turned on and the bell rang.

On one occasion, Popov found in the experiment that the distance of the receiver to detect the electric wave suddenly increased much more than usual.

"What is going on here?" Popov checked and found that he could not find a reason.

One day, Popov accidentally found a wire on the metal chip detector. He took the wire off and the bell didn't ring; he narrowed the experimental distance so close, and the bell rang again.

Popov was overjoyed and quickly connected the wire to one end of the metal chip detector and the other end of the detector. After retesting, the results show that the signal transmission distance increases dramatically after using the antenna.

The radio antenna was born.

1. According to the nature of work, it can be divided into transmitting antenna and receiving antenna;

2, according to the use can be divided into communication antennas, broadcast antennas, TV antennas, radar antennas, etc.;

3. According to the directionality, it can be divided into an omnidirectional antenna and a directional antenna;

4, according to the working wavelength can be divided into ultra long wave antenna, long wave antenna, medium wave antenna, short wave antenna, ultra short wave antenna, microwave antenna, etc.;

5, according to the structure and working principle can be divided into line antennas and surface antennas. Describe the characteristic parameters of the antenna with direction pattern, directivity coefficient, gain, input impedance, radiation efficiency, polarization and bandwidth;

6. Divided by dimension can be divided into two types: one-dimensional antenna and two-dimensional antenna.

One-dimensional antenna: It consists of a number of wires, either straight lines like those used on mobile phones, or some dexterous shapes, like the old bunny ears used on televisions before cables appear. Unipolar and dipole antennas are the two most basic one-dimensional antennas.

Two-dimensional antennas vary widely, with sheets (a square metal), arrays (a bundle of well-organized two-dimensional patterns), flared, and dished.

7, the antenna can be divided into three categories according to the use of the occasion: handheld antenna, vehicle antenna, base antenna.

Handheld antenna: It is the antenna for personal use of the walkie-talkie. There are two types of rubber antennas and whip antennas.

Car antenna: refers to the communication antenna originally designed and installed on the vehicle. The most common application is the suction cup antenna. The vehicle antenna structure also has an antenna in the form of a shortened type, a quarter-wavelength, a centrally-sensed type, a five-eighth wavelength, and a double-half wavelength.

Base station antenna: It plays a very important role in the entire communication system, especially as a communication station for communication hubs. Commonly used base station antennas are FRP high-gain antennas, four-ring array antennas (eight-ring array antennas), and directional antennas.

Second, some indicators:

Antenna efficiency

It refers to the ratio of the power radiated by the antenna (ie, the power that effectively converts the electromagnetic wave portion) to the active power input to the antenna. It is a value that is always less than one.

Antenna polarized wave

When electromagnetic waves propagate in space, if the direction of the electric field vector remains fixed or rotates according to a certain law, the electromagnetic wave is called a polarized wave, also called an antenna polarized wave, or a polarized wave. Usually divided into plane polarization (including horizontal and vertical polarization), circular polarization and elliptical polarization.

Polarization direction

The direction of the electric field of the polarized electromagnetic wave is called the polarization direction.

Polarized plane

The plane formed by the polarization direction and the propagation direction of the polarized electromagnetic wave is called a polarization plane.

Vertical polarization

The polarization of radio waves often uses the earth as the standard surface. A polarized wave whose plane of polarization is parallel to the normal plane (vertical plane) of the earth is called a vertically polarized wave. The direction of the electric field is perpendicular to the earth.

Horizontal polarization

A polarized wave whose plane of polarization is perpendicular to the normal plane of the earth is called a horizontally polarized wave. The direction of the electric field is parallel to the earth.

Planar polarization

If the polarization direction of the electromagnetic wave is maintained in a fixed direction, it is called plane polarization, also called linear polarization. In the component of the electric field parallel to the earth (horizontal component) and the component perpendicular to the surface of the earth, the spatial amplitude has an arbitrary relative magnitude, and plane polarization can be obtained. Both vertical and horizontal polarization are special cases of planar polarization.

Circular polarization

When the angle between the plane of polarization of the radio wave and the normal plane of the earth changes from 0 to 360°, that is, the magnitude of the electric field does not change, the direction changes with time, and the trajectory at the end of the electric field vector is perpendicular to the plane of propagation. When the projection is a circle, it is called circular polarization. Circular polarization can be obtained when the horizontal component and the vertical component of the electric field have equal amplitudes and the phases are different by 90° or 270°. Circular polarization, if the polarization plane rotates with time and has a right-handed relationship with the electromagnetic wave propagation direction, it is called a right circular polarization; otherwise, if it is a left-handed spiral relationship, it is called a left circular polarization.

Elliptical polarization

If the angle between the plane of polarization of the radio wave and the normal plane of the earth changes periodically from 0 to 2π, and the trajectory at the end of the electric field vector is an ellipse projected on a plane perpendicular to the direction of propagation, it is called elliptical polarization. Elliptical polarization can be obtained when the amplitude and phase of the vertical and horizontal components of the electric field have arbitrary values ​​(except when the two components are equal).