Research On Far-field-near-field Transformation Methods In Over-The-air-testing

The introduction of massive multiple-input multiple-output(Massive MIMO)and millimeter wave(mmWave)communication technologies have realized the high-speed transmission of data for a large number of users in the era of 5th-Generation(5G)mobile communications,which has significantly improved the performance of the communication system.With the rapid development of 5G technology,manufacturers need to con-duct more comprehensive performance testings on smart terminals during production.Over the air(OTA)testing is a widely used method to evaluate the radio performance of antenna systems.However,the ideal far-field-based OTA testing will be limited by cost,space and distance in practice.This thesis focuses on the research of the far-near-field transformation method in OTA testing,and studies the ideal far-field simulation scheme in OTA radio frequency(RF)performance testing and OTA system perfor-mance testing.Antenna testing is an important research topic in OTA RF perfor- mance testing.Direct far field(DFF),compact antenna testing range(CATR)and near field transformation(NFTF)are the mainstream solutions for antenna testing.The plane-wave generator(PWG)radiation system has become a popular method for near-field antenna testing due to its ad-vantages in cost and test distance.The key to studying PWG is to design the locations and weights of PWG elements to satisfy the required accuracy of the far-field distribution.In the traditional method,the theory of non-redundant sampling representation was exploited to sample the locations of the PWG radiating source.This thesis proposes two new locations sam-pling methods based on the similarity of the synthetic field and the orthog-onal matching pursuit(OMP)algorithm,and respectively simulates and analyzes the errors of the synthetic field and the target field,verifying the superiority of the proposed methods over the traditional method.Further-more,this thesis also proposes a new convex optimization frame to sup-press radiation energy in the outer zone around the antenna under-test(AUT).For OTA system performance testing,reverberation chamber method(RC),radiated two-stage method(RTS)and multi-probe anechoic chamber method(MPAC)are the three mainstream solutions.Among them,the MPAC method is the only OTA testing method that can fully support Mas-sive MIMO in principle,so this thesis defines this method as the basic so-lution for Massive MIMO OTA testing in simulation.In the near-field environment of the MPAC,there will be a problem of multi-user interference caused by insufficient sinking of the trough(zero depth)of the spatial spectrum of the signal at the receiving end.In order to avoid the near-field effect and solve the problem from the root,this thesis proposes an amplitude and phase modulation network structure based on the error adjustment matrix to replace the anechoic chamber,thereby sim-ulating the ideal far-field effect.Since the error of the near-field effect re-flected in the spatial spectrum is not very large,in order to be able to solve this problem well,the problem of insufficient adjustment accuracy of the basic amplitude and phase modulation network structure must be consid-ered.Therefore,this thesis chooses to add the corresponding error adjust-ment matrix in the channel emulator(CE),and improve the space spectrum together with the basic amplitude and phase modulation network,so that the ideal far-field effect can be further achieved.This thesis simulates and analyzes the spatial spectrum error obtained under the near-field effect and the proposed method,which verifies the ef-fectiveness of the proposed method to solve the problem.