Antenna principle

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1. Antenna principle

1.1 Definition of antenna:

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.

1.2 The function of the antenna:

Energy conversion-the conversion of guided traveling waves and free space waves;

Directional radiation (receiving)-has a certain directionality.

1.3 Principle of antenna radiation

1.4 Antenna parameters

Radiation parameters

Half-power beam width, front-to-back ratio;

Polarization mode, cross-polarization discrimination rate;

Directivity coefficient, antenna gain;

Main lobe, side lobe, side lobe suppression, zero point filling, beam downtilt...

Circuit parameters

Voltage standing wave ratio VSWR, reflection coefficient Γ, return loss RL;

Input impedance Zin, transmission loss TL;

Isolation degree Iso;

Passive third-order intermodulation PIM3…

Antenna side lobe

Horizontal beam width

Front-to-back ratio: specify the ratio of the forward radiation power to the antenna and the backward radiation power within ±30°

The relationship between gain and antenna size and beam width

Flatten the "tire", the more concentrated the signal, the higher the gain, the larger the antenna size, and the narrower the beam width;

Several key points of antenna gain:

The antenna is a passive device and cannot generate energy.

Antenna gain is just the ability to effectively concentrate energy to radiate or receive electromagnetic waves in a specific direction.

The gain of the antenna is produced by the superposition of the elements.

The higher the gain, the longer the antenna length.

The gain is increased by 3dB and the volume is doubled.

The higher the antenna gain, the better the directivity, the more concentrated the energy, and the narrower the lobe.

1.5 Radiation parameters

Polarization: Refers to the trajectory or changing state of the electric field vector in space.

1.6 Circuit parameters

Return loss

In this example, the return loss is 10log(10/0.5) = 13dB

VSWR (Standing Wave Ratio) is another measure of this phenomenon

Isolation: It is the ratio of the signal received by one polarization of the other polarization

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