Do you know how to test a mobile phone antenna?
Among the radio frequency components of mobile phones, the mobile phone antenna is a passive component. As the only tailor-made device on the mobile phone, its particularity and importance inevitably require very strict requirements for the antenna performance test in the development process. Ensure the normal use of mobile phones.
Here briefly introduce 3 common mobile phone antenna test methods in the research and development process of mobile phone antenna.
1. Microwave anechoic chamber (Anechoic chamber)
The anechoic chamber is also called a non-reflective chamber and an anechoic chamber for short.
The microwave anechoic chamber is composed of an electromagnetic shielding room, filtering and isolation, grounding device, ventilation waveguide, indoor power distribution system, monitoring system, and microwave absorbing materials.
It is a shielded room with absorbing materials as the backing surface, which can absorb most of the electromagnetic energy incident on the six walls, which is a good simulation of free-space conditions.
The darkroom is a piece of test equipment that antenna design companies need to build, because the test of mobile phone antennas is more accurate and systematic, and its test indicators can be used to measure the performance of a mobile phone antenna.
Mainly used by antenna companies, but its cost is expensive.
2. TEM CELL test
Use TEM CELL to test antenna active indicators, because the cost of a microwave anechoic chamber and antenna test system is relatively expensive, generally more than one million yuan. The general mobile phone design and research and development companies do not have such equipment and use TEM CELL instead of testing.
Similar to the test purpose of the microwave anechoic chamber, TEM CELL is also an antenna test environment that simulates an ideal space. The metal box can provide sufficient shielding function to eliminate the influence of external interference on the antenna, and the internal absorbing material can also absorb the incident wave and reduce Small reflected waves.
TEM CELL cannot perform passive testing on antennas, only active indicators.
Due to space constraints, the absorbing material of the TEM CELL is relatively thin. For the wedge-shaped absorbing material, the incident wave is absorbed through the increase of multiple reflections between the wedge tips. Therefore, the absorbing material in the microwave anechoic chamber is relatively thick. TEM CELL’s absorbing materials are not purchased thick, so the absorption of incident waves is not very sufficient, which will lead to inaccurate test results.
In addition, the height of the TEM CELL is not enough, which is one reason why the TEM CELL cannot be used for quantitative testing.
According to the far-field test analysis of antenna radiation, for the mobile phone antenna of the EGSM/DCS frequency band, the distance between the tested mobile phone and the antenna is at least 1 meter; therefore, we can see that almost all 2D darkrooms are much greater than this distance.
The TEM CELL is smaller than this distance, so this is also one of the reasons why the TEM CELL is inaccurate compared to the microwave anechoic chamber.
Therefore, TEM CELL can only do a qualitative analysis of the antenna but not a quantitative analysis.
In the laboratory, you can qualitatively analyze the differences between several prototypes and compare their performance, but it cannot be used as an accurate standard value to measure the performance of the antenna. It can only be roughly judged by comparing it with other golden samples’ performance.
TEM CELL generally only finds the best square value, making the test result more sensitive to the location of the phone.
In addition, there is a kind of test tool that is better than a shielded box. Some design companies use it for active testing of mobile phone antennas. This method is not feasible.
On the one hand, because the test distance is too close, on the other hand, because there is not enough absorbing material, external interference has a greater impact on the antenna test. This makes the test result more sensitive to the position. A slight change in the position will cause a big change in the test result. Therefore, this test method has little reference significance to the performance of mobile phone antennas.
3. Use the coupling test board to test the antenna performance
In order to ensure the production quality of the product during the production process, antenna coupling tests are often performed.
The test device to be used is:
The coupling test fixture is connected with the comprehensive tester, and the mobile phone is fixed on the fixture.
In the early stage of production, based on the test results of several prototypes, a reasonable coupling compensation value is determined, a power standard is determined, and then the maximum power of the mobile phone is tested. Higher than this power standard means that the product meets the production requirements, and lower than this requirement.
There is a problem with the antenna and related components. The following problems can be found through the antenna coupling test:
(1) Welding and missing parts of the antenna matching circuit.
(2) There is a problem with the electronic/structural parts around the antenna.
(3) The antenna is not assembled properly.
(4) There is a problem with the quality of the antenna itself.
It should be pointed out that the antenna coupling test is a product conformance test, not a product performance test.
The antenna indicators mentioned above are all tested for the far field. The antenna coupling test is for the near field. The antenna of the mobile phone under test is very close to the coupling fixture antenna.
The near field is the objective existence of the antenna itself. Once the structure and antenna of the entire mobile phone are determined, the near field can also be determined. Therefore, it can be judged whether there is a problem with the antenna part according to whether the test result is within a certain range.
The antenna coupling test only tests the maximum power of the antenna and does not test other items. Even if it is tested, it is meaningless.
It is very wrong to use the antenna coupling test to verify the performance of the antenna and to judge the performance according to the test results of different mobile phones.
At present, many domestic mobile phone companies judge the performance of antennas through coupling tests, which makes antenna companies have to pass the coupling test standards by adjusting the resonant frequency offset.
In terms of mobile phone antenna design, antenna testing is a very important part. Without an accurate design, there is nothing to measure whether the antenna design is good or bad, so choosing a good test system is also very important to the development of mobile phone antennas.
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