At present, mobile phone RF performance testing are increasingly concerned about the radiation performance of the test machine. This performance reflects the radiation emitted and received the final performance of the phone. There are two ways to inspect the radiation properties of mobile phones：One is from the radiation performance of the antenna to determine, Conventional antenna testing methods，which is called passive test；The other is in particular inside an anechoic chamber to test mobile phone radiation power and receive sensitivity,which is called active test。OTA(Over The Air) test belongs to active test。
The passive test focuses on the gain, efficiency, and efficiency of the mobile phone antenna, Direction chart to investigate the radiation performance of the mobile phone.
Although the passive test takes into account the influence of the environment on the antenna performance. But the antenna and the whole machine after the combination of transmit power and receive sensitivity, can not directly know.
OTA testing is focused on the radiation performance of the mobile phone from the transmitter power and the receiving sensitivity of the mobile phoneActive test is in specific microwave darkroom, testing machine in all directions in three-dimensional space of transmit power and the receiving sensitivity of more directly reflect the radiation performance of a mobile machine.
CTIA(Cellular Telecommunication and Internet Association) relevant standards of OTA(Over The Air)。OTA test focused on the performance of the whole machine testing, and gradually become the mobile phone manufacturers to pay attention and recognition of the test project.
The purpose of OTA testing
Only through FTA (FullType Approval) certification test phone models to go on sale. IDuring the FTA test，RF performance test mainly mobile phones in the cable connection mode；Cell phone radiation emission and reception performance machine， FTA test is not clearly defined, OTA test just to make up for the shortage。At the same time, terminal manufacturers must clearly understand the radiation performance of the production of mobile phones. Increase the transmission and reception of cell phone radiation index through various measures. If performance is poor cell phone radiation will cause the phone signal is not good, poor voice quality, easily dropped, which is also the problem of customer complaints.
When the phone call, because the human brain near the phone antenna, the lower transmit and receive performance of mobile phones, mobile phone radiation machine will reduce the transmit and receive performance. In the mobile phone R & D process should measure the quantitative impact of the human brain to transmit and receive performance of mobile phones, and to optimize the design, so that transmit and receive performance degradation is not too large, a reduction of electromagnetic coupling effects of the human body and the antenna.
In order to investigate cell phone radiation, in addition to study the performance of mobile phone antenna passive, active performance of the machine is also an important aspect of the study. The current overall performance more and more terminal manufacturers active attention, and therefore the two should be in the study of radiation properties of mobile phone radiation properties taken together. At present the terminal antenna manufacturers in research and development are generally required antenna suppliers of passive and active test report.
OTA test and other main parameters of the phone
The main test parameters and the related calculation of the OTA test are the radiation performance parameters，which divided into two categories: receiving and transmitting parameters.
Emission parameters is TRP、NHPRP；Receiving parameters is TIS、NHPIS。
TRP(Total Radiated Power)：Through the area of the radiation power of the whole radiating surface and the average obtained. It reflects the transmit power of the mobile phone, which is related to the transmission power and the radiation performance of the mobile phone.
NHPRP(Near Horizon Partial Radiated Power)：Parameters reflecting the transmit power of the antenna near the H surface of the handset.
TIS(Total Isotropic Sensitivity)：Reflect the sensitivity of the entire radiation spherical cell phone receiver. It reflects the receiving sensitivity of the mobile phone, and it is related to the sensitivity of the mobile phone and the radiation performance of the antenna.
NHPIS(Near Horizon Partial Isotropic Sensitivity)：Parameters of the receiver sensitivity of the antenna near the H surface.
For the handheld terminal, the OTA test will examine the end of the above parameters in the simulation of the head, the comparison of the parameters of the relevant parameters in the case of no simulation.
When examining the performance of the antenna, there are other parameters that need to be understood：APIP、Gain、Directivity、EIRP、ERP。
Gain(dBi)：At the same input power, the ratio of the antenna to the power of a point source antenna at the same point in the space of a point in space. The gain unit is dBi, and the gain of the antenna test report provided by the handset antenna manufacturer is generally dBi as a unit.
Gain(dBd)：At the same input power, the ratio of the antenna to the maximum radiation direction of the half wave dipole antenna at a certain point in space is dBd.
Directivity：In the same radiation power, the ratio of the power generated by the antenna to the same point in the same point as the ideal source of the antenna.
Efficiency：Ratio of antenna radiation power and antenna input power.
APIP(Antenna Port Input Power)：The power of the antenna port is the size of the output of the PA. The power size is mainly related to the transmission power of the mobile phone.
EIRP(Effective Isotropic Radiated Power)：The equivalent omnidirectional radiation power is the product of the antenna’s power and the gain of the antenna to the dBi, which reflects the power of the antenna to radiate in all directions.
PEIRP(Peak Effective Isotropic Radiated Power)：Peak equivalent isotropic radiated power.
ERP(Effective Radiated Power) is the same as EIRP, but ERP is the product of the antenna’s power and the gain of dBd.
TRP and SAR index in OTA test
TRP reflects the radiation performance of the antenna far field, while the SAR is reflected by the near field radiation performance of the antenna. For the OTA in the index of the Trp, Trp is relatively large, so from the PA out into the power to the antenna to be effective radiation, the connectivity of the wireless interface is better. In the SAR test, it is hoped that the TRP value is relatively small, so that the human brain to absorb the power is relatively small, to ensure that the SAR test standards. As a result, the TRP index and SAR index are a pair of contradictory indicators, how to ensure that the design of the antenna to meet the relevant standards, to meet the needs of the design, in the beginning of the antenna design must be considered.
Some of the solutions：
(1) The most important is to choose the right antenna form。Monopole in the antenna has a high efficiency, but the SAR is also high, so it should be recognized before use, that is, the Monopole and the human brain has a strong coupling effectPIFA antenna has good comprehensive performance, because of its close to the human brain, the PCB of the ground cover, the high frequency band in the human brain than the maximum radiation direction has 5-6dB attenuation, As a result, the PIFA value of SAR antenna is relatively low, and it is an ideal antenna in the antenna.
(2) At the beginning of the design of the antenna, the SAR problem is considered. Combining the structure of mobile phone with the appropriate form of antenna, the performance of the antenna is ensured by SAR index. For example, take the antenna placed at the bottom of the PCB and other measures. For an external spiral antenna, we should pay attention to the distance between the antenna and the human brain, and ensure the needs of the SAR test.
(3) In the late design, the discovery of SAR testing standards, can be resolved through the way to improve the performance of the antenna, such as the use of slightly larger material and other methods, which need to cooperate with the antenna manufacturers.
(4) Change the antenna line mode, adjust the direction of the map and other measures.
(5) Reducing the output power of PA in the case of standard.
The above method is to meet the needs of the SAR and TRP test, to achieve a compromise between the two.
OTA’s CTIA test index directly reflects the radiation performance of the mobile phone, so it is more and more important for the testing organizations and related manufacturers. In the evaluation of mobile phone antenna parameters, the passive and active performance index is considered, and the performance of the antenna is evaluated comprehensively.