Probe Design And Research Of Near-field Antenna Measurement System

Antenna measurement system as a device to detect the performance of the antenna,the methods used cover the frequency domain,time domain,space domain and digital domain,these technologies have their own advantages and disadvantages,but the frequency domain measurement is widely used at present.Among them,near field antenna measurement is favored in the field of frequency domain measurement.The whole system contains active and passive equipment.Among passive equipment,the probe is the most critical,and its performance indicators will affect the measurement results.If the probe bandwidth in the system is greater than the antenna to be measured,multiple types of antennas can be measured without frequent replacement of probes,which will reduce the measurement operation process.In addition,if the probe has dual-polarization characteristics,signals in two polarization directions can be measured during measurement.Compared with the single-polarization probe,it is not necessary to control the rotating manipulator to conduct secondary scanning.If the probe is composed of array scanning,the measurement time will be further reduced.In view of the narrow bandwidth and scanning time of the traditional probe,this paper mainly studies the ultra-wideband dual-polarization probe in the antenna measurement system,and carries on the array design on this basis.In the face of the actual demand of UWB probe,we start from two types of planar antenna,one is the gradient slot antenna.The gradient slot antenna is linear and exponential(Vivaldi),and the loading resistance and the grid slot miniaturization technology are adopted.The size of the linear gradient slot line is157.5mm×151.3mm×151.3mm.The working frequency band is 0.4GHz-6GHz,the in-band standing-wave ratio is less than 2.5,the port isolation degree is less than-20 d B,the direction diagram is symmetrical,the maximum gain can reach 7d Bi,the total size of the exponential type is 170mm×110mm×110mm,the working frequency band is 0.4GHz-6GHz,the in-band standing-wave ratio is less than 2,Port isolation below-20 d B,maximum gain in the band can reach 8.4d Bi;The other is the printed dipole antenna.After the miniaturization technology of the previous type and the orthogonal dual-polarization design,the printed dipole antenna has a fixed size of 160mm×56mm×56mm,a working frequency band of0.4GHz-6GHz,and an internal standing-wave ratio of less than 2.5.The radiation performance of the direction patterns of plane E and plane H is generally good in the frequency band.The isolation degree between the two ports is better than-20 d B in most frequency bands,and the axial cross-polarization ratio is basically less than-15 d B.Finally,the physical test is verified.Secondly,according to the planar multi-probe measurement system,a 1×4 linear array is designed with a printed oscillator probe,and the electrical performance between the elements is simulated and analyzed.Although the array elements may be affected by the adjacent probes,the standing wave ratio still remains below 2.5.Array design has accelerated the near-field scanning speed and the array in the near-field measurement system also needs corresponding feed network design,therefore,a simple design points and eight Wilkinsion power splitters,impedance matching with three circular arc type,and finally in the whole frequency band,power splitters S11 below-10 d B,transmission loss and isolation degree also basic within the normal range.