The third-order intermodulation of the base station antenna plays an important role in system operation, which not only affects the quality of communication signal, but also an important performance of the R&D level of antenna enterprises. The following is a brief analysis of this problem:
1、 Internal factors
There are many kinds of base station antennas, and the structures of different models and types of antennas are also complex. In particular, the integrated beautifying antenna has derived various beautifying enclosures due to different application environments. Due to the limitation of enclosure shape, the design difficulty is much greater than that of a conventional antenna. Throughout the antenna industry, the intermodulation index of a beautified antenna is generally worse than that of conventional antenna, which is also determined by the existing technical level. I won’t describe it in detail. Let’s analyze several places that have a great impact on antenna indicators.
a. Effects of cable assemblies
At present, Din 7 / 16 cable components are widely used in base station antennas. When purchasing feeder components, it is necessary to ensure that the intermodulation index is qualified, which is the entrance link affecting intermodulation. If the feeder components can not pass intermodulation, it is impossible to judge the following influencing factors. The influence of cable components on intermodulation mainly lies in the material properties of DIN head and the connection process between cable and din head. The intermodulation index with good process control is good and stable.
b. Fixing effect of Din 7 / 16 cable head
In the production process, due to the different operation standards of production workers, the operation intermodulation results of different personnel with the same materials will be different, but this difference can be avoided as far as possible. Try to use standardized installation tools, especially the same tightening force and firm as far as possible, so as to avoid the change of intermodulation test results during the transportation of storage boxes.
c. Influence of feeder junction box
The antenna feeder junction box is one of the culprits that make intermodulation impossible. The most important factor affecting the intermodulation index of the junction box is the coating on the inner surface of the junction box. In order to save costs, some suppliers have adopted some materials containing trace ferromagnetic components, resulting in the intermodulation index has not met the requirements.
d. Influence of solder wire quality
In the process of antenna assembly and welding, the quality of solder wire used is one of the important factors that directly affect the intermodulation index. In order to reduce costs, some enterprises do not hesitate to purchase inferior welding materials, which may be unprofessional or limited identification conditions, resulting in low product passing rate and unnecessary losses to enterprises. Therefore, in order to achieve good intermodulation index, test before purchasing solder wire, and then buy it after confirming that there is no problem.
e. Influence of fixing screw material
In the process of product research and development, it is found that the material of screws, nuts and elastic flat pads used to fix antenna components is one of the important factors affecting antenna intermodulation index. The screws, nuts and elastic flat pads for fixing antenna components shall be products without ferromagnetic materials as far as possible. Once mixed products are mixed, it will bring serious economic losses to the production of the enterprise.
f. Influence of phase shifter
The phase shifter has an important influence on the intermodulation index of electrically tunable antenna. The performance of the structured phase shifter is also closely related to the strength of the material itself and the contact surface, which is also the core technology of the electrically tunable antenna.
2、 External factors
In addition to the factors of the antenna itself, there are also test reasons that affect the results of antenna intermodulation.
a. Influence of intermodulation on the stability of the testing instrument
Before testing the product, first determine the stability and reliability of the equipment itself. The simplest way is to test the reliability and stability of the intermodulation results with good intermodulation load after starting up and preheating for a certain time, that is, to see whether the load test results are consistent with the previous test results under the same conditions. If they are consistent, it means that the machine itself is OK, and the following tests can be carried out.
b. Influence of intermodulation test line
The test line belongs to vulnerable materials in the test system, and the theoretical plugging times are 500 times, but it is far more than this number in practical application. In order to save the test cost, general enterprises use it until it can not meet the use requirements. The damage of the cable is mainly at the connection between the cable and the connector, which is easy to be considered damaged in the process of use. It is recommended to handle with care during use, and do not bend the cable and connection too much so that the service life of the cable will be longer.
c. Human factors
Some testers are not professional enough in the use process. For example, the preheating time of the machine is too short, the personnel are too close to the product, the cable is bent at will, and the tightness of the cable head is uncertain. These are the uncertain factors affecting the test results. Try to use torque wrench to screw the cable head, eliminate the influence of the above human factors, and finally get more accurate results.
d. External environment
The installation position of the antenna is also one of the important factors affecting the intermodulation index of the antenna. For example, there are obstacles in front of the antenna, especially metal billboards and lightning flat iron on the roof, which have a great impact on the intermodulation index, and should be avoided in the actual installation process.
