A Study Of 5G Base Station Antenna Testing Method

With the vigorous development of 5G communication technology.In the communication base station and terminal equipment,the antenna has new requirements in terms of quantity and form,which puts forward higher requirements for antenna measurement.In the OTA test of 5G base station antenna,the spherical multi-probe near-field measurement has obvious advantages.In this paper,the UWB dual-polarization probe and the spherical near-far field transformation algorithm in the spherical multi-probe near-field OTA measurement system are studied.In the spherical multi-probe near-field measurement system,the dual-polarized probe antenna needs as wide frequency band as possible and as small size as possible.Firstly,based on the traditional Vivaldi antenna,an ultra-wideband single-polarized Vivaldi antenna with a working frequency range of 0.4 GHz to 6 GHz,which is designed by means of loading resistance,slot loading,and dielectric loading,the VSWR of the antenna is less than 2.4 and the size is 170mm*110mm.The antenna pattern has a good symmetry in the frequency band and meets the design requirement.Secondly,two ultra-wideband Single-polarized Vivaldi antennas are crosswise embedded to form an ultra-wideband dual-polarized probe antenna.The dual-polarized probe antenna is optimized by simulation.In the frequency range,the VSWR is less than 2.5;the isolation between two ports is greater than 32 d B,and the farfield radiation pattern is good.In the multi-probe measurement system,the mutual coupling between the probes affects the accuracy of antenna measurement.Therefore,a circular array consisting of 23 ultra-wideband dual-polarized probes is designed,the isolation between the simulated array elements is greater than 20 d B.Although the array elements are affected by the mutual coupling of adjacent array elements,the VSWR of each port are less than 2.5,and the radiation pattern is symmetric and meets the engineering needs.The spherical near-field to far-field transformation algorithm has been studied in detail from two aspects: Scattering Matrix Theory and Mode Expansion Theory.Both algorithms are based on the spherical wave function,but the difference between the two theory is that the scattering matrix theory is based on the idea of a microwave network,and the measured antenna and probe are considered as a two-port network,the transmission coefficient is solved by the probe response constant and the near-field data,the transmission coefficient of the near-field and the far-field are same,and the far-field radiation pattern of the antenna can be obtained by substituting the transmission coefficient into the far-field transmission equation.The mode expansion theory is based on the field around the measured antenna,the field weighted stack by Spherical wave function.The weighted coefficients can be obtained by the near field data and the orthogonal relationship of the spherical wave modes,and the far-field pattern of the antenna under test can be obtained.Finally,two kinds of near-field to far-field transformation program without probe compensation algorithms are compiled by MATLAB.In order to verify the correctness and versatility of the two algorithms,the near field date of S-band standard gain cone horn,UWB single polarization Vivaldi antenna and UWB dual polarization probe antenna,which is brought into two near-field to far-field transformation algorithms program to obtain the far-field pattern of the measured antenna.The transformation values of the two algorithms program are highly consistent with the simulation values of HFSS,and the coincidence between the two algorithms is also high.