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4 test methods for 5G base station antenna OTA
Source:Originally | Author:Calio Huang of C&T RF Antennas Inc | Publish time: 2019-05-03 | 2667 Views | Share:

The advantages of the single-probe near-field test are a small footprint, the low construction cost of the darkroom, simple structure of the turntable, easy installation and disassembly of the device under test, low space loss, and comparison of the test results and far-field test results in CW mode. Close. The disadvantage is: due to structural reasons, the data acquisition of the antenna back flap is incomplete; there is only one test probe, the efficiency of testing the 3D pattern is less than that of the multi-probe sphere; the collected data needs to be followed by near-far field conversion.

4. Problems and solutions

The current OTA test solution, whether it is a far-field solution or a near-field solution, can test the radiation pattern of a 5G base station antenna in CW mode. However, regarding the radiation performance test of radio frequency indicators, the current far-field scheme is limited by the large path loss, and only the parameters with high power levels such as EIRP, EVM, occupied bandwidth, and EIS can be tested. For downlink RF indicators with particularly low power levels, such as ACLR, switching time templates, and spurious emissions, it is difficult to test after a long distance test distance and attenuated to a lower noise level. When measuring the uplink indicator, the interference signal sent by the auxiliary signal source is attenuated by the path of the far field, and it is difficult to reach the power level required for the RF index test such as ACS, in-band blocking, and co-location blocking, which also brings difficulties to the test. Although the path loss of the near-field test scheme is much lower than that of the far-field, the method of taking the reference phase in the broadband service signal mode is still problematic, and the RF radiation test result is still far from the expected value.

Since the indicators required for test verification in the laboratory R&D test phase are comprehensive, the far field test method of compact or loss reduction should be adopted for this type of test. By shortening the far-field test distance, increasing the horn antenna gain, using low-loss RF cables, and shortening the RF line cabling distance within a certain range, the path loss can be greatly reduced, and the far-field scheme can be extended to test RF indexes such as ACLR and ACS. The path loss of the compact field itself is much smaller than that of the far field, and it can measure more RF targets than the far field. However, there are still some RF indicators that are particularly low due to their own power. How to reduce path loss is not enough. At this stage, it can only be tested by conduction. For the production line test, the test cost is low, the efficiency is high, space is small, and the typical index can be tested. The single-probe near-field test scheme is more suitable. As for the future 5G high-band test, due to the higher frequency and more serious loss, far-field testing will become less suitable, and conduction testing will be more difficult, requiring a combination of near-field testing inductive near-field testing. The far-field conversion algorithm requires a reference signal, which requires the equipment manufacturer and the measurement instrument manufacturer to solve the problem of taking reference signals from the device.