| With the gradual evolution of 5G communication technology,driverless technology and satellite networking technology,the demand for millimeter wave(mm-wave)wireless communication,radar,remote sensing and telemetry is more and more urgent,so the evaluation of wireless performance in this band is particularly important.Accurate and efficient over the air(OTA)test system is required for 5G mm-wave terminals,antenna front ends of CPE and other equipment,as well as vehicle borne radar and satellite systems.As the only effective means to test the transmitting and receiving performance of 5G terminal antenna,the core technology of OTA measurement includes near-field measurement theory and algorithm,high-performance probe antenna and special mm-wave absorbing materials,among which the demand for high-performance probe antenna in 5G mm-wave band is particularly urgent.Ultra wideband dual-polarized horn antenna is considered as an ideal candidate for high frequency mm-wave probe antenna due to its good directivity,large power capacity and low loss.In this paper,the mm-wave dual-polarized horn antenna is studied as follows:1.Research on mm-wave broadband double-ridged horn antenna(DRHA).In order to make the horn antenna have wider bandwidth,ridge structure is usually introduced into the horn.This kind of antenna is also called ridged horn antenna.So,it is necessary to research DRHA before studying dual-polarized quad-ridged horn antenna(QRHA).After a certain understanding of the DRHA,we know that with the frequency of the traditional DRHA gradually expanding to high frequency in the wide band,the phase difference of the electromagnetic wave on the antenna aperture gradually increases,resulting in the splitting of the main lobe of the pattern and the decrease of the gain.Therefore,this paper improves the antenna structure,by adding wedge structure in the feed waveguide and replacing the side wall of H-plane horn,the problem of pattern splitting is effectively solved.The designed antenna works at 18-54GHz(VSWR < 2),covering 5G NR FR2 completely.The gain variation is small in the whole frequency band,and the typical value is about 14 d B.The 3d B beamwidth of E-plane and H-plane is relatively stable with frequency variation.In the aspect of machining,considering the machining accuracy,machining cost and assembly difficulty,a set of reasonable machining and assembly scheme is proposed.After testing the prototype,the measured results are in good agreement with the simulation results,which proves that this design and production scheme is feasible and effective.The proposed mm-wave DRHA can be used as the calibration antenna of the measurement system.2.Research on mm-wave dual-polarized quad-ridged horn antenna(QRHA).(a)Based on the research experience of DRHA,we introduce two pairs of mutually orthogonal ridged plates into the circular waveguide,which are excited by coaxial feedlines respectively,to realize the dual polarization characteristics of the antenna.The simulation results show that in the range of 18-54 GHz,the reflection coefficients of the two ports are basically less than-10 d B,the isolation between two ports is greater than 30 d B,and the cross-polarization discrimination(XPD)is more than 20 d B.However,in the high frequency band,the maximum radiation direction of the main lobe will shift to the axial direction.(b)The structure of the antenna is improved.Part of the horn wall is used to dissipate the high-order modes excited in the feed waveguide,thus reducing the contribution of the high-order modes to the antenna aperture field,and finally improving the pattern performance.The simulation results show that the improved antenna keeps good matching characteristics and significantly improves the problem of pattern offset,and the gain of the two ports is basically the same in the whole frequency band.In the processing,the idea of block processing is adopted,and the high-precision machining method is selected.Finally,a high-precision prototype is obtained.Through the test in the anechoic chamber,the data show that the measured results are in good agreement with the simulation results.(c)Research on OTA near-field measurement system.The designed antennas are applied to a set of mm-wave spherical nearfield measurement system,which is used as system calibration antenna and probe antenna respectively.Finally,the performance of the antennas and the system is tested by measuring the linear and circular polarization antennas.The data show that the antennas designed in this paper has good performance,which can meet the requirements of the test system,and cooperate with the system to complete the test of antenna performance. |
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