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Introduction to antenna knowledge: definition and basic parameters of antenna

  • Categories:News Center
  • Time of issue:2021-02-02 09:37
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(Summary description)The antenna system is a system composed of a transmitting antenna and a receiving antenna. The former is a transmission mode converter that transforms the radio frequency current or electromagnetic wave in the guided wave mode into a space electromagnetic wave in the diffuse wave mode; the latter is the transmission mode converter for its inverse conversion.

Introduction to antenna knowledge: definition and basic parameters of antenna

(Summary description)The antenna system is a system composed of a transmitting antenna and a receiving antenna. The former is a transmission mode converter that transforms the radio frequency current or electromagnetic wave in the guided wave mode into a space electromagnetic wave in the diffuse wave mode; the latter is the transmission mode converter for its inverse conversion.

  • Categories:News Center
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  • Origin:technology light up the future published in information
  • Time of issue:2021-02-02 09:37
  • Views:
Information

The antenna system is a system composed of a transmitting antenna and a receiving antenna. The former is a transmission mode converter that transforms the radio frequency current or electromagnetic wave in the guided wave mode into a space electromagnetic wave in the diffuse wave mode; the latter is the transmission mode converter for its inverse conversion.

As a transmitting antenna for mode conversion of guided traveling wave to diffuse wave, and a receiving antenna for mode conversion of diffused wave to guided wave mode I, except that the power carrying capacity and voltage withstanding capacity of the transmitting antenna are much greater than that of the receiving antenna, both are It can be used interchangeably, and the basic characteristic parameters of the antenna remain unchanged, which is called the reciprocity theorem. Another important function of the antenna is the concentration of electromagnetic wave energy, that is, when used as a transmitting antenna, the energy is concentrated in the transmitting direction while reducing energy in other directions; when used as a receiving antenna, more energy can be intercepted from incoming waves in the receiving direction. For incoming waves in other directions, the input energy is reduced by phase cancellation. This is the directivity of the antenna. Compared with non-directional antennas, the increase in energy concentration is called antenna gain. The extended meaning of antenna directivity is the negative gain (attenuation) in the non-communication direction, which can be used to describe another related performance index of the antenna, that is, the side lobe (interference) radiation suppression of the transmitting antenna or the incoming wave interference of the receiving antenna in the non-communication direction Inhibition.

1. Definition of mobile communication antenna system


Definition and scope of antenna system

In the mobile communication system, the communication antenna is the converter of the circuit signal of the communication device and the electromagnetic wave radiated from space.


2. Description of the performance parameters of the base station antenna

General Electric Index

1. Frequency Range 

Working frequency band: No matter the antenna or other communication products, it always works within a certain frequency range (bandwidth), which depends on the requirements of the index. Normally, the frequency range that meets the index requirements can be the operating frequency of the antenna.

The width of the working frequency band is called the working bandwidth. Generally, the working bandwidth of an omnidirectional antenna can reach 3-5% of the center frequency, and the working bandwidth of a directional antenna can reach 5-10% of the center frequency.

 
2. Input Impedance

Input impedance: The ratio of the signal voltage to the signal current at the input of the antenna is called the input impedance of the antenna. Generally, the input impedance of a mobile communication antenna is 50Ω.

The input impedance is related to the structure, size, and operating wavelength of the antenna. Within the required operating frequency range, the imaginary part of the input impedance is small and the real part is quite close to 50Ω, which is necessary for the antenna to be in good impedance matching with the feeder.

3. Voltage standing wave ratio (VSWR)

Voltage standing wave ratio: The voltage standing wave ratio of an antenna is the ratio of the maximum value to the minimum value of the voltage standing wave pattern generated along the transmission line when the antenna is used as the load of a lossless transmission line.

The standing wave ratio is caused by the superposition of reflected waves generated by the incident wave energy transmitted to the input end of the antenna and not fully absorbed (radiated). The greater the VSWR, the greater the reflection and the worse the match. In mobile communication systems, the standing wave ratio is generally required to be less than 1.5.

4. Isolation

Isolation represents the proportion of signals fed to one port (one polarization) of a dual-polarized antenna that appear in the other port (another polarization).

5. Third Order Inter modulation 


Third-order intermodulation signal: refers to the parasitic signal after two signals are in a linear system. Due to the existence of nonlinear factors, the second harmonic of one signal and the fundamental wave of another signal are beaten (mixed).

Intermodulation phenomenon is a phenomenon in which two or more carrier frequencies outside the frequency band are mixed and the new frequency components fall in the frequency band, causing the system performance to degrade.

6. Power Capacity

Power capacity: The power capacity of an antenna refers to the maximum continuous RF power that can be continuously added to the antenna within a specified time period under specified conditions without reducing its performance.

Space radiation index

7. Gain

The ratio of the radiated power flux density of the antenna in a specified direction to the maximum radiated power flux density of the reference antenna (usually an ideal point source) at the same input power;

Antenna gain is used to measure the ability of an antenna to send and receive signals in a specific direction. It is one of the important parameters for selecting a base station antenna. The higher the antenna gain, the better the directivity, the more concentrated the energy, and the narrower the lobe.

8. Horizontal/Vertical Half Power Beam Width (H/V-Plane Half Power Beam Width)

In the main lobe of the power pattern, the beam width angle between two points where the relative maximum radiation direction power drops to half or less than the maximum 3dB is called the half-power lobe width.


The half-power beam width in the horizontal plane is called the horizontal beam width; the half-power beam width in the vertical plane is called the vertical beam width.

9. Electrical Down Tilt (Electrical Down Tilt)

Electric downtilt refers to the angle between the maximum radiation direction of the vertical radiation surface of the communication antenna and the antenna normal.

Communication antennas are classified into fixed downtilt antennas and electrically adjustable antennas according to whether they support electric downtilt adjustment: fixed downtilt antennas refer to fixed downtilt antennas produced by shaping the antenna radiating element array in amplitude and phase according to wireless coverage requirements; and Electrically adjustable antenna means that the phase difference of different radiating elements in the array is changed by a phase shifting unit to produce different radiation main lobe downtilt states. Generally, the downtilt state of an electrically adjustable antenna is only within a certain adjustable angle range.

10. Front-to-Back Ratio

The front-to-back ratio of the antenna refers to the ratio of the power flux density in the maximum radiation direction of the main lobe (specified as 0°) to the maximum power flux density near the opposite direction (specified as within the range of 180°±30°) F/B= 10log (front and rear power / backward power).

11. Side lobe suppression and zero fill (Elevation Upper Side lobes & Null Fill)

Side lobe suppression: The side lobe of the main lobe in the vertical direction (that is, the positive direction of the zenith angle) is called the upper side lobe. In order to cover the effect of the base station antenna, a certain mechanical downtilt is usually adopted for the antenna in the network planning. This may cause the first upper side lobe of the antenna (or within a certain angle range) to be in a horizontal position or even lower than the horizontal position, which may easily cause interference in the neighboring area. Therefore, it needs to be suppressed, that is, upper side lobe suppression.

The upper side lobe not only wastes the energy radiated by the antenna, but also interferes with adjacent cells, especially high-rise buildings in adjacent cells. Therefore, the upper side lobe should be suppressed as much as possible, especially the first upper side lobe with larger energy.

Zero point filling: It means that the first zero point of the lower side lobe is filled by beamforming design in the vertical plane of the antenna to improve the coverage of the near area of ​​the base station and reduce the dead zone and blind spots of the near area coverage.

12. Cross Polarization Ratio (Cross Polarization Ratio)

The difference between the power level of the antenna with the same polarization reception (the maximum reception level) and the power level of the different polarization reception (the minimum reception level) within the 3dB beam width of the pattern

13. Circularity of the direction map (Circularity)

 
The pattern circularity of an omnidirectional antenna refers to the deviation of its maximum or minimum level value from the average value in the horizontal plane pattern.

The average value refers to the arithmetic average of the dB value of the level in the horizontal plane pattern with the maximum interval not exceeding 5°.

14. Polarization (Polarization)

The electric field direction of the electromagnetic wave radiated by the antenna is the polarization direction of the antenna. If the electric field direction of the electric wave is perpendicular to the ground, we call it a vertically polarized wave; if the electric field direction of the electric wave is parallel to the ground, it is called a horizontally polarized wave; if the electric field direction of the electric wave is at an angle of 45° with the ground, it is called It is +45° or -45° polarization.

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