1 Introduction
With the continuous development of mobile communications, mobile communication antennas have also experienced the development of single-polarized antennas, dual-polarized antennas, smart antennas, MIMO antennas, and even large-scale array antennas. After the 4G development, China Mobile currently has about 1.5 million base stations. The quality of the network feeders is uneven. Antennas, as sensing organs of mobile communication networks, have become more and more important in the network and have become more and more important. Although the investment in the antenna is relatively small (only about 3% of the base station investment), more than 40% of network failures are caused by the antenna system. The degraded quality of the antenna feeder system will lead to poor coverage performance or cause interference problems. Moreover, as a complex passive product, the antenna is difficult to monitor in the network.
The performance of antenna feeder system problems is varied. For example, after two or three years of using the antenna, the network coverage performance is significantly reduced, and the intermodulation interference becomes more and more serious; the susceptibility to standing wave ratio alarms in the event of heavy rain; the standing wave ratio alarm in severe winds The same type of antenna used by the same manufacturer in the same network performance is very different. These phenomena indicate that the supplier's product reliability is not high, the quality is hidden, and the product life indicator is not met. How to judge? This is related to the antenna's consistency, stability, and reliability.
2, the reliability of the antenna
In general, the reliability of a product refers to the ability or possibility that a component, a product, or a system performs a specified function without failure under certain conditions within a certain period of time. The reliability of the product can be evaluated by reliability, failure rate, and mean time between failures. Environmental reliability refers to the ability of a product to fulfill specified functions within a specified period of time under specified conditions. In the process of designing and applying products, the products are constantly subjected to the impact of their own and external climate and mechanical environment, but they still need to be able to work normally. This requires verification using test equipment.
Reliability includes three elements: durability, maintainability, and design reliability. Durability refers to the use of product failure-free or the length of life. Maintainability means that when a product fails, it can be quickly and easily repaired or repaired.
Design reliability is the key to product quality. Due to the complexity of human-machine systems, and the possible errors in human operations and the impact of operating environment, the possibility of errors still exists. So when designing, Must take full account of the product's ease of use and ease of operation, which is the design reliability. Therefore, reliability is an important quality indicator. Qualitative description is not enough. It must be quantified so that accurate description and comparison can be made. The quantitative representation of reliability has its own characteristics, and it is difficult to fully represent it with one feature quantity due to the different occasions.
The reliability test of the antenna product can be judged through a series of tests. The reliability test is an important measure for the reliability investigation, analysis and evaluation of the antenna product. Antenna reliability tests include high and low temperature tests, rain tests, vibration tests, impact tests, crash tests, automotive transport tests, wind load tests, ice capture tests, and power tests. The environmental test can verify the reliability of the antenna product structure. As shown in Fig. 1, after the rain test, vibration test, and high-power test, the antenna that satisfies the reliability requirements and the unmatched comparison test results.
Figure 1. Antenna structure reliability comparison test
It can be seen from the figure that the antenna with poor reliability can be tested through the environmental test, and the environmental test can test the reliability of the design, material and process of the antenna product.
3, the stability of the antenna performance
Product stability refers to the ability of a product to maintain its characteristics constant over time, usually referring to the ability of a product's characteristics to remain unchanged over time. Stability can be characterized quantitatively, mainly to determine the relationship of characteristics over time. Stability is very important, so how can we know if the system is stable?
Product stability and reliability are inseparable. For the stability of the antenna product, a relatively simple method is to judge the reliability of the antenna performance through the coincidence degree of the index curve before and after the reliability test. found in study:
(1) The radiation parameters are insensitive to the process and the circuit, and the circuit parameters are sensitive to the circuit and process. In the production process, especially for multiple debugging, the circuit parameters are easily affected;
(2) In the circuit parameters, the magnitude of intermodulation is too small, and it is sensitive to test methods, test equipment and environment. It is not suitable for statistical evaluation;
(3) The circuit parameters have low requirements on the test site and can be tested on site. The radiation parameters require high reflex and shielding properties at the test site and cannot be field tested.
Therefore, it is recommended to select the standing wave ratio and isolation in the circuit parameters as the stability characterization parameter of the antenna performance.
Figure 2. Comparison of antenna VSWR performance stability
As shown in Fig.2, it is the comparison of the VSWR performance stability of the antenna before and after the vibration test. The antenna of the left figure shows that the standing wave of the antenna before and after the vibration test basically does not change well, and the antenna of the figure on the right shows the signal after the vibration test. The wave ratio is still acceptable (VSWR<1.5), but the deviation of the standing wave ratio before and after the test is large, and it can be considered that the antenna is less stable.
Figure 3 shows the comparison of antenna isolation performance stability before and after the water spray test. It can be seen that the left antenna isolation stability is better, and the right is worse.
Figure 3: Comparison of antenna isolation performance stability
Although the antenna with poor antenna stability can often pass the network test, the quality of the antenna is often degraded due to changes in the natural environment during the use cycle, which leads to a decrease in network quality and is prone to occur in the introduction.
4. Uniformity of antenna performance
The consistency of antenna performance refers to the consistency of the parameter performance of the antenna products of the same model, which can be judged by comparing the similarity of the index curves of multiple products of the same type. As shown in Figure 4, the VSWR curves of multiple antennas of the same type are compared for consistency. The VSWR curves of the multiple antennas on the left show the same tendency and the deviation is small, indicating that the VSWR performance of this type of antenna is relatively consistent. The standing wave ratio curve of multiple antennas in the right figure is not regular, and it is relatively messy, indicating that the VSWR performance of this type of antenna is less consistent. Figure 5 shows the consistency of antenna isolation performance. The left antenna is better than the right antenna isolation parameter. Therefore, it can be considered that the left antenna performance is better than the right antenna.
Figure 4. Comparison of antenna VSWR performance consistency
Figure 5. Consistency comparison of antenna isolation performance
5 Conclusion
The antenna is a broadband, low-Q passive product. It will not be restored after the material structure is damaged during the reliability test. The frequency change caused by the thermal expansion and contraction of the material during the high-low temperature test is neglected, and the test index after the comparison test is changed. The condition is sufficient to reflect the stability of the electrical performance index, and it is not necessary to test the index during the reliability test. The intermodulation index of the antenna is sensitive to the manufacturing process and structural stability. Dynamic testing can be used to indirectly verify product stability.
In short, the reliability, stability and consistency of the antenna have an important impact on the mobile communication network. It is of great significance to measure and control the antenna performance before the antenna product enters the network.
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