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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 | 859 Views | Share:

 

Figure4. Single-probe near-field test system

3. Comparison of advantages and disadvantages of each test plan

The advantage of the far field test is that since the receiving antenna is larger than the far field criterion from the transmitting antenna, the electromagnetic wave is approximated to the plane wave when the transmitting antenna propagates to the receiving antenna, and the collected data does not need to be converted by the far field, and the test device can transmit the high power signal. Test modulated wideband signals, support multi-user testing, and more. The disadvantage is that because the test distance needs to be larger than the far field criterion, the test site has a large area and high construction cost. Taking an antenna with a diameter of 1 m and operating in the 3.5GHz band as an example, the far-field condition is calculated to be greater than 25 m according to the far-field criterion formula. The farther the test distance is, the closer the electromagnetic wave radiation is to the plane wave, but at the same time it will bring about the problem of too much space loss. In addition, since the far field test generally has only one probe, a single test can only draw a section of the antenna radiation sphere. If you want to obtain the 3D pattern of the entire radiation sphere, you need to measure multiple times on different sections, test time. And the cost of testing has increased dramatically.

The advantages of the compact field test are: Significantly reduced site size compared to the far field, which greatly reduces site construction costs and measurement path loss. The test results are closest to direct far-field testing and can test CW waves and business signals. Thanks to the reduced path loss, it can measure more RF radiation than the far field solution. The disadvantage is: similar to the short-field test, the 3D pattern test is less efficient, and the other is the mirror cost and post-maintenance cost.

The advantages of the multi-probe spherical near-field test are: small footprint, single-test giving 3D pattern, high test efficiency, low space loss, and the pattern test results in CW mode are close to the far-field test results. The disadvantage is: the upper limit of the receiving power of the test system is low. When the 5G base station is tested for full power transmission, the receiving device must be pre-fadered; the measurement data needs post-processing for near-far field conversion; the near-far field conversion requires a reference phase. At present, the measurement results in the service signal mode are still unsatisfactory due to the problem of the reference phase.