Discussion on antenna consistency, stability, reliability and measurement methods

Jacktang

Discussion on antenna consistency, stability, reliability and measurement methods [Copy link]

1. Introduction With the continuous development of mobile communications, mobile communication antennas have also experienced a development process from single-polarization antennas, dual-polarization antennas to smart antennas, MIMO antennas and even large-scale array antennas. After the rapid development of 4G, China Mobile currently has about 1.5 million base stations, and the quality of antennas and feeders in the network varies. As the sensor organ of the mobile communication network, the status of antennas in the network is becoming more and more complex and more and more important. Although the investment in antennas accounts for a small proportion (only about 3% of the investment in base stations), more than 40% of network failures are caused by antenna feed systems. The degradation of antenna system quality will lead to poor coverage performance or interference problems. In addition, antennas are complex passive products that are difficult to monitor in the network. Antenna system problems manifest themselves in a variety of ways, such as: after two or three years of use, network coverage performance has significantly declined, and intermodulation interference has become increasingly serious; standing wave ratio alarms during heavy rain; standing wave ratio alarms during strong winds; antennas of the same model from the same manufacturer have very different performances when used in the same network, etc. These phenomena indicate that the reliability of the supplier's products is not high, there are quality risks, and the product life index requirements cannot be met. How to judge? This is related to the consistency, stability and reliability of the antenna. 2. Reliability of the antenna Generally, product reliability refers to the ability or possibility of components, products, and systems to perform specified functions without failure within a certain period of time and under certain conditions. The reliability of a product can be evaluated by reliability, failure rate, mean interval between failures, etc. Environmental reliability refers to the ability of a product to complete the specified function under specified conditions and within a specified time. During the design and application process, the product is constantly subjected to the influence of itself and the external climate and mechanical environment, and it still needs to be able to work normally, which requires the use of test equipment to verify it. Reliability includes three major elements: durability, maintainability, and design reliability. Durability refers to the trouble-free use or service life of the product. Maintainability refers to the ability to quickly and easily eliminate the fault through maintenance or repair when a product fails. Design reliability is the key to determining product quality. Due to the complexity of the human-machine system, the possible errors that may exist in human operation, and the influence of such factors as the operating environment, the possibility of errors still exists. Therefore, the ease of use and operability of the product must be fully considered during design. This is design reliability. Therefore, reliability is an important quality indicator. It is not enough to describe it qualitatively. It must be quantified so that it can be accurately described and compared. The quantitative representation of reliability has its own characteristics. Due to different usage scenarios, it is difficult to fully represent it with a characteristic quantity. The reliability of antenna products can be determined through a series of tests. Reliability testing is an important means of investigating, analyzing and evaluating the reliability of antenna products. Antenna reliability tests include high and low temperature tests, rain tests, vibration tests, impact tests, collision tests, automobile transportation tests, wind load tests, ice capture tests and power tests. Environmental tests can be used to test the reliability of antenna product structures. As shown in Figure 1, the antennas that meet the reliability requirements and those that do not meet the requirements are compared after rain tests, vibration tests and high-power tests.

Figure 1. Antenna structure reliability comparison test

As can be seen from the figure, antennas with poor reliability can be detected through environmental tests, and environmental tests can test the reliability of antenna product design, materials and processes. 3. Stability of antenna performance Product stability refers to the ability of a product to keep its characteristics constant over time, usually refers to the ability of a product's characteristics not to change over time. Stability can be quantitatively characterized, mainly to determine the relationship between characteristics and time changes. Stability is very important, so how can we know whether the system is stable? Product stability and reliability are inseparable. How to judge the stability of antenna products? A relatively simple method is to judge the reliability of antenna performance by the overlap of the index curves before and after the reliability test. Through research, it is found that: (1) Radiation parameters are not sensitive to process and circuit, while circuit parameters are sensitive to circuit and process. In the production process, especially multiple debugging, it is easy to affect the circuit parameters; (2) Among the circuit parameters, the intermodulation magnitude is too small, and it is sensitive to the test method, test equipment and environment, and has large fluctuations, which is not suitable for statistical evaluation; (3) Circuit parameters have low requirements for the test site and can be tested on site. Radiation parameters have high requirements for the reflection and shielding characteristics of the test site and cannot be tested on site. Therefore, it is recommended to select the standing wave ratio and isolation in the circuit parameters as the parameters to characterize the stability of the antenna performance. Comparison of the stability of antenna standing wave ratio performanceComparison of the stability of antenna standing wave ratio performance

Figure 2, Comparison of the stability of antenna standing wave ratio performance

As shown in Figure 2, it is a comparison of the stability of the antenna voltage standing wave ratio performance before and after the vibration test. The antenna on the left has basically no change in standing wave ratio before and after the vibration test, and the curves are in good agreement. However, the antenna on the right still passes the standing wave ratio test after the vibration test (VSWR<1.5), but the standing wave ratio curves before and after the test have large deviations, so it can be considered that the antenna has poor stability. Figure 3 is a comparison of the stability of antenna isolation performance before and after the water spray test. It can be seen that the antenna isolation stability in the left figure is better, while that in the right figure is worse.

Figure 3, Comparison of Antenna Isolation Performance Stability

Antennas with poor antenna stability can often pass the network access test, but their quality often deteriorates during their use period due to changes in the natural environment, resulting in a decline in network quality, and are prone to the phenomenon described in the introduction. 4. Consistency of antenna performance The consistency of antenna performance refers to the consistency of the parameter performance of antenna products of the same model, which can be judged by comparing the approximation of the index curves of multiple products of the same type. As shown in Figure 4, it is a consistency comparison of the voltage standing wave ratio curves of multiple antennas of the same type. The standing wave ratio curves of multiple antennas on the left have the same trend and small deviation, indicating that the standing wave ratio performance of this type of antenna is relatively consistent; the standing wave ratio curves of multiple antennas on the right are irregular and messy, indicating that the consistency of the standing wave ratio performance of this type of antenna is poor. Figure 5 is a consistency comparison of antenna isolation performance. Similarly, the antenna on the left has better consistency in isolation parameters than the antenna on the right. Therefore, it can be considered that the consistency of the performance of the antenna on the left is better than that of the antenna on the right. Figure 4. Comparison of consistency of antenna VSWR performances. Figure 5. Comparison of consistency of antenna isolation performances. 5. Conclusion. Antennas are broadband, low-Q passive products. During reliability tests, the material structure will not be restored after being damaged. The frequency changes caused by thermal expansion and contraction of the material during high and low temperature tests are negligible. The changes in test indicators after the comparison test are sufficient to reflect the stability of the electrical performance indicators, and there is no need to test the indicators during reliability tests. The intermodulation indicators of antennas are 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 antennas have an important impact on mobile communication networks. It is of great significance to measure and control these performances of antennas before antenna products are connected to the network.