Antenna is an indispensable part of wireless transmission, in addition to our use of optical fiber, cable, network cable, etc. to transmit wired signals, as long as it is in the air using electromagnetic wave propagation signals, various forms of antennas are required.

First, the basic principle of the antenna

The basic principle of the antenna is that the high-frequency current produces a changing electric field and magnetic field around it, according to Maxwell's electromagnetic field theory, "the changing electric field produces a magnetic field, and the changing magnetic field produces an electric field", so that the continuous excitation realizes the propagation of wireless signals.

Electromagnetic fields

Second, the gain coefficient

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

Third, antenna efficiency

It refers to the ratio of the

power radiated out of the antenna (that is, the power of the electromagnetic wave part that is effectively converted) to the active power input to the antenna. is a constant value less than 1.

Fourth, polarized antenna polarized wave

When electromagnetic waves propagate in space, if the direction of the electric field vector remains fixed or rotates according to certain laws, this electromagnetic wave is called polarization wave, also known as antenna polarization wave, or polarization wave. It can generally be 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 surface

The plane formed by the polarization direction

and propagation direction of polarized electromagnetic waves is called the polarization plane.

Vertical polarization

　　Vertical polarization

The polarization of radio waves is often based on the earth as the standard plane. Any polarization wave that is parallel to the normal surface of the earth (perpendicular plane) is called a vertical polarization wave. Its electric field direction is perpendicular to the earth.

Horizontal polarization

　　Horizontal polarization

Any polarization wave that is perpendicular to the normal surface of the earth is called a horizontal polarization wave. Its electric field direction is parallel to the earth.

Vertical polarization & amp; amp; Horizontal polarization

Plane polarization

　　Planepolarization

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

Circular polarization

　　Circular Polarization

When the angle between the polarization surface of the radio wave and the normal surface of the earth changes from 0~360° period, that is, the size of the electric field remains unchanged, the direction changes with time, and the trajectory at the end of the electric field vector is projected as a circle on the plane perpendicular to the propagation direction, it is called circular polarization. When the horizontal and vertical components of the electric field have equal amplitudes and a phase difference of 90° or 270°, circular polarization can be obtained. Circular polarization, if the polarization surface rotates with time and has a right helix relationship with the direction of electromagnetic wave propagation, it is called right circular polarization; Conversely, if the left spiral relationship is formed, it is called left circular polarization.

Elliptic polarization

　　Elliptical Polarization

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