Antenna feeder guarantees microwave relay communication

Zhao Zuqing, Henan Provincial Microwave Communication Bureau

The antenna feeder system is one of the important components of microwave relay communication. The antenna plays the role of converting electromagnetic waves transmitted in the feeder into electromagnetic waves propagating in free space, or converting electromagnetic waves propagating in free space into electromagnetic waves propagating in the feeder. The feeder is the transmission channel of electromagnetic waves. In the microwave relay communication circuit of the multi-channel shared antenna feeder system, the technical performance and quality index of the antenna feeder system directly affect the communication quality of each microwave channel of the shared antenna feeder system.

Antenna installation inspection

When installing and commissioning the antenna feeder system, strictly follow the technical specifications for construction and commissioning. Because there are hidden projects in the installation process of the antenna feeder system, once the hidden projects have hidden quality problems, they will leave trouble for future maintenance. At this stage, we must strictly control the quality of installation and commissioning, and do the following construction inspections:

1. There should be no collision between the antenna and the iron tower on the feeder to prevent force deformation and affect the technical performance.

2. Check the height and orientation of the antenna installation according to the construction design drawings, and the installation components should be fastened well.

3. When the feeder is bent and twisted, the bending radius and twisting angle should meet the requirements of the feeder manufacturer.

4. When making feeder flanges, be careful not to leave broken copper chips in the feeder waveguide. When the feeder is connected to the antenna, the connector cannot be stressed, but must be connected naturally. Do not pull the hard connection strongly by screws to prevent the feeder or antenna feeder source from being damaged by long-term force. This link should prevent hidden quality problems.

5. The antenna feeder grounding should be reliable and good. The grounding device must be tinned before connecting to the galvanized parts of the iron tower. Each feeder must have three grounds, located at the back of the antenna, 1 meter from the iron tower on the feeder and in front of the machine room.

6. The feeder should be fixed firmly, and the fixed spacing should not exceed the requirement of once every 1.2 meters to prevent the feeder from being damaged by the wind blowing and swinging for a long time.

Antenna feeder debugging

1. Antenna orientation adjustment: Send the standard level at the sending end, and repeatedly adjust the transceiver antenna to make the receiving level meet the design requirements.

2. Standing wave ratio (S): In the whole frequency band, the standing wave ratio of the antenna feeder at the top of the microwave rack should not be greater than 1.15. If the indicators are not met, check whether the connectors of the antenna feeder are well matched, and whether the bending radius and torsion angle of the feeder meet the requirements.

3. Cross-polarization decoupling degree (XPD): This indicator plays an important role in reducing cross-polarization interference by co-frequency heteropolarization multiplexing. If the index is not qualified during the test, the polarization direction of the antenna feeds of the two transceivers can be adjusted.

4. Feeder attenuation: The attenuation value of each feeder cannot be higher than the design value. If it fails, check whether the feeder is deformed by collision and whether the joint is well matched. If the environment humidity is too high during construction, check whether the feeder is seriously damp or condensed.

5. Inflatable air pressure: Inflatable air pressure is 1300Kpa, and it should not be less than 1100Kpa after 24 hours. Otherwise, check whether the antenna feeder is well sealed and the inflator is working properly.

Troubleshoot of antenna feeder system

In the microwave relay communication circuit of the multi-channel common antenna feeder system, the antenna feeder system failure has two main features. One is that the same fault phenomenon occurs simultaneously on each channel of the common antenna feeder system during the fault. The second is that the fault of the antenna feeder system is manifested in the circuit as the reception level drops and the circuit noise rises. Common failures are: antenna azimuth deviation; feeder collision deformation; inadequate sealing into the water; polarization decoupling reduction and so on. In the maintenance, you can judge what kind of failure is based on the characteristics of the failure, and then supplement with the necessary instrument test to analyze and determine the cause and location of the failure.

With the development of microwave communication to unattended, the network management system provides powerful monitoring and management for the equipment and circuit quality in the circuit, but it has not provided monitoring function for the antenna feeder system. It is envisaged that the antenna feeder system will be included in monitoring and management, which will definitely improve the maintenance efficiency and quality. According to actual needs, set up two monitoring points in the antenna feeder system. One is the inflation part, which is easier to achieve, because the inflator has a remote signal interface to transmit the inflation pressure change to the network management system; the second is the antenna orientation, which is also a part that is more prone to failure in actual maintenance. You can detect the reception level of each channel of the common antenna feeder system, set the correspondence between the reception level and the antenna orientation, and indirectly reflect the antenna orientation.

Through the above analysis, we can see that the feeder system is a common channel for microwave multi-channel signals. The technical performance and quality index directly affect the quality of the microwave communication circuit, and the fault affects a wide area. The working environment of the system is harsh and uncontrollable. The strong wind, rain, snow and lightning have a great influence on the antenna feeder. In severe cases, the antenna feeder will be damaged. The antenna feeder must be protected. The quality of installation and commissioning is the basis of the stable work of the antenna feeder system. Once there is a hidden quality problem in the construction of the project, it will cause serious consequences for future maintenance. Once the feeder system is damaged, the repair time is long and the fault duration is long.

Excerpt from "Communication Industry News"

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