Basic knowledge and applications of antennas-Antenna installation specifications for mobile communication systems

Due to the rapid development of mobile communications, there are multiple networks coexisting in many areas of the country, that is, the three networks A, B, and G coexist. G networks in some areas also include GSM9000 and GSM1800. In order to make full use of resources and realize resource sharing, we generally adopt the form of antennas sharing towers. This involves the correct installation of the antenna, that is, how to install it to minimize the mutual influence between the antennas. In engineering, we generally use the isolation index to measure, usually the isolation should be at least greater than 30dB. In order to meet this requirement, the method of separating the antennas in the vertical direction or in the horizontal direction is often used. Practice has proved that the distance between the antennas At the same time, vertical installation can obtain greater isolation than horizontal installation.

　　 Generally speaking, the antenna installation should pay attention to the following issues:

(1) Tower-side installation of the directional antenna: In order to reduce the influence of the antenna tower on the antenna pattern, attention should be paid to the installation: when the distance from the center of the directional antenna to the tower is λ/4 or 3λ/4, the outside of the tower can be obtained The maximum directionality.

　　 (2) Tower-side installation of omnidirectional antenna: In order to reduce the influence of the antenna tower on the antenna pattern, in principle, the antenna tower cannot be the reflector of the antenna. Therefore, during installation, the antenna should always be installed on the corners and the closest distance between the antenna and any part of the tower should be greater than λ.

　　 (3) Multi-antenna sharing tower: Try to reduce the coupling and mutual influence between the transmitting and receiving antennas of different networks and try to increase the isolation between the antennas. The best way is to increase the distance between them. When the antennas share a tower, vertical installation should be preferred.

(4) For traditional single-polarized antennas (vertical polarization), due to the isolation (≥30dB) between the antennas (RX-TX, TX-TX) and the requirements of space diversity technology, a certain amount of The horizontal and vertical separation distance, the general vertical distance is about 50cm, and the horizontal distance is about 4.5m. At this time, capital investment must be increased to expand the antenna installation platform. For dual-polarized antennas (±45° polarization), due to ± The polarization orthogonality of 45° can ensure that the isolation between the +45° and -45° antennas meets the requirement of intermodulation for the isolation between the antennas (≥30dB), so the space separation between dual-polarized antennas It only needs 20-30cm, and the mobile base station does not need to build an iron tower. It only needs to erect an iron column with a diameter of 20cm, and fix the dual-polarized antenna on the iron column according to the corresponding coverage direction.

Summary
--- Distance from the tower platform: >1M
--- Antenna spacing:
--- Receive antennas in the same subdivision set: >3M
--- Horizontal distance of omnidirectional antenna: >4M
--- Horizontal distance of directional antenna: >2.5M
--- Vertical distance between antennas on different platforms: >1M
--- The transceiver antenna cannot be placed upside down unless specified in the manual.
--- In the protection range of lightning rod.
--- Antenna azimuth: For directional antennas, the first sector is 60 degrees east of north, the second sector is south, and the third sector is 60 degrees west of north.
--- Antenna tilt angle: ensure that the actual antenna tilt angle meets the SE design requirements, and the error is less than 2 degrees.
--- Antenna verticality: Except for base stations with antenna inclination, ensure that the antenna verticality is not more than 2 degrees.