Mobile phone antenna test in practice

With the rapid development and application of mobile communication, China’s mobile phone industry has been developing and expanding, and of course, China’s mobile phone users are also growing rapidly. In the radio frequency devices of mobile phones, mobile phone antenna is a passive device. As the only “customized” device on mobile phones, its particularity and importance inevitably require that the research and development process of the antenna performance test requirements are very strict, to ensure the normal use of mobile phones. Now a brief introduction to the development of a mobile phone antenna in the process of several common mobile phone antenna test methods:

1. Anechoic chamber

An anechoic chamber is also called an anechoic chamber and anechoic chamber. The microwave anechoic chamber consists of an electromagnetic shielding room, filter and isolation, grounding device, ventilation waveguide, indoor distribution system, monitoring system, absorbing material, and other parts. It is a shielded room with absorbing the material as the lining. It can absorb most of the electromagnetic energy emitted to the six walls to better simulate the free space conditions. Darkroom is the test equipment that antenna design companies need to build, because the test of mobile phone antenna is more accurate and systematic, and its test index can be used to measure the performance of a mobile phone antenna. It’s mainly used by antenna companies, but it’s expensive.

2. TEM CELL test

TEM CELL is used to test the active index of antenna, because the cost of a microwave anechoic chamber and antenna test system is relatively expensive, generally more than a million, the general mobile phone design and development companies do not have such equipment, and TEM CELL(also more than triangular cone) to replace the test. Like the microwave anechoic chamber, TEM CELL is 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, while the internal absorbing material can also absorb incident waves and reduce reflected waves. TEM CELL can not conduct a passive test on the antenna, but only on the active index. Due to space limitations, TEM CELL of absorbing material is thin, and for chopping absorbing material, is through the split multiple reflections between the sharp increase of incident wave absorption, therefore the absorbing material in the microwave darkroom are thick, and TEM CELL of the absorbing material purchase and thick, so the absorption of incident wave is not good, so lead to the test result is not accurate.

Also, the height of the TEM CELL is not enough, which is one of the reasons why TEM CELL cannot be quantitatively tested. According to the far-field test and analysis of antenna radiation, for the mobile phone antenna in EGSM/DCS frequency band, the distance between the tested mobile phone and the antenna is at least 1 meter; As a result, we can see that almost all 2D darkrooms are much larger than this distance. However, TEM CELL is smaller than this distance, which is one of the reasons why TEM CELL is inaccurate compared with microwave anechoic chamber.

Therefore, TEM CELL can only do a qualitative analysis of antenna, but not quantitative analysis. In the laboratory, we 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. The performance of the mobile phone antenna can only be roughly judged by comparing with other “Golden samples”.TEM CELL generally only finds the best square value, making the test result more sensitive to the position of mobile phone.

Also, there is a test tool than a shielding box, some design companies used to conduct active testing of mobile phone antenna, this method is not feasible. On the one hand, because the test is too close, on the other hand, as there were not enough absorbing material, external disturbance of antenna test impact is bigger, so that lead to the test result is more sensitive to position, change a little bit about the position of test results is larger change, so the test of the performance of the antenna don’t have much reference value.

3. Test antenna performance with the coupling test board

To ensure the production quality of the product, the coupling test of the antenna is often carried out. The test device to be used is: the coupling test fixture is connected to the comprehensive tester, and the mobile phone is fixed on the fixture. At the early stage of production, according to the test results of several prototypes, a reasonable coupling compensation value is given to determine a power standard, and then the maximum power of the mobile phone is tested. Higher than this power standard means that the product meets the production requirements, while lower than this requirement means that there are problems with the antenna and related devices. The following problems can be found through the antenna coupling test:

(1) virtual welding of antenna matching circuit and missing parts, etc.

(2) problems with the electronic/structural components around the antenna.

(3) the antenna is not properly assembled.

(4) there is something wrong with the antenna quality.

It should be pointed out that the antenna coupling test is a product consistency test, not a test of product performance. The antenna indexes mentioned above are all tests for the far-field, and the antenna coupling test is a test for the near field. The antenna of the tested mobile phone is very close to the antenna of the coupling fixture. The near field is the objective existence of the antenna itself. Once the structure and antenna of the whole mobile phone are determined, the near field can also be determined. Therefore, whether the antenna has problems or not can be judged according to the test results within a certain range. Antenna coupling test is only for the maximum power of the antenna test, not for other items of the test, even if the test, it is meaningless.

It is very wrong to use an antenna coupling test to verify the performance of the antenna and to judge the performance according to the test results of different phones. At present, I still encounter many domestic mobile phone companies, which judge the performance of the antenna through the coupling test, so that the antenna company has to pass the coupling test standard by adjusting the resonant frequency.

For the design of mobile phone antenna, antenna test is a very important link, there is no accurate design, antenna design is good or bad there is nothing to measure, so choose a good test system for the development of mobile phone antenna is also very important.

From:http://www.hj-antenna.com/mobile-phone-antenna-test-practice/